solubles

ˈsɒljʊbəl

1. (Chemistry) (of a substance) capable of being dissolved, esp easily dissolved in some solvent, usually water

2. capable of being solved or answered

El Diccionario de la lengua espanola es la obra lexicografica de referencia de la Academia.

La vigesimotercera edicion, publicada en octubre de 2014 como colofon de las conmemoraciones del tricentenario de la Academia, es fruto de la colaboracion de las veintidos corporaciones integradas en la Asociacion de Academias de la Lengua Espanola (ASALE).

Los materiales solubles son aquellos que pueden diluirse en otro material hasta formar una sustancia nueva. La solubilidad puede indicarse en moles, gramos o miligramos por litro, incluso en porcentaje de soluto con un solvente especifico.

No todos los materiales son igual de solubles en determinados solventes, esto depende de las propiedades de las moleculas que constituyen cada material y de las reacciones entre ambos compuestos al solubilizarse.

Al momento de formar una solucion, el tamano de las moleculas y las fuerzas entre los iones juegan un papel fundamental.

Un material es facilmente soluble si se disuelven mas de 10 miligramos de soluto por cada litro de solvente.

El azucar a 20 oC tiene una solubilidad en agua de 1330 gramos por cada litro de agua. Esta propiedad hace que el azucar se emplee con frecuencia para endulzar comidas, postres y bebidas.

La sal comun tiene una solubilidad en agua de 359 gramos por cada litro. Analogo al caso anterior, la alta solubilidad de la sal hace posible el uso de este material con fines domesticos y culinarios.

Tanto el alcohol etilico (bebidas alcoholicas) como el alcohol isopropilico (antiseptico de uso medico) se disuelven en agua de manera sencilla.

El vinagre se disuelve facilmente en el agua. Es por esto que su uso es tan propicio para la preparacion de ensaladas e incluso para limpieza de algunas superficies.

En caso de que se desee aclarar el tono de color de una pintura, es factible diluir un poco de esta en agua.

Lo anterior es valido siempre que la pintura sea base acuosa; en las pinturas con base de aceite no aplica dada la baja solubilidad de los compuestos oleosos.

Los endulzantes artificiales, como el aspartame y la sacarina, tambien son altamente solubles en agua gracias a su composicion quimica.

Es un antiseptico soluble en agua empleado en el ambito medico como antibiotico de amplio espectro. Tambien se utiliza para la esterilizacion de utensilios medicos.

Esta sal antiseptica es muy utilizada en la industria de alimentos como conservante de bebidas carbonatadas, salsas, bandejas de frutas y vegetales, jugos, margarinas y jaleas.

Es una practica comun en el hogar emplear una disolucion de desinfectante en agua para limpiar los pisos de las casas, e incluso para la desinfeccion de otras superficies como topes de ceramica o granito.

Es un polvo cristalino empleado como conservante en la fabricacion de productos cosmeticos. Se emplea predominantemente en soluciones acuosas, por su solubilidad en agua.

Este material es uno de los mas utiles y multifaceticos que existe. Dada su elevada solubilidad en agua es utilizado con fines medicos, cosmeticos y domesticos.

Esta sal es altamente soluble en agua y hoy en dia es recomendada como coadyuvante en el tratamiento de malestares estomacales. Tambien es usada como materia prima en la elaboracion de fertilizantes de suelos.

Capacity of a substance to dissolve in a solvent in a homogeneous way

In chemistry, solubility is ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution.

The extent of the solubility of a substance in a specific solvent is generally measured as the concentration of the solute in a saturated solution, one in which no more solute can be dissolved.^[1] At this point, the two substances are said to be at the solubility equilibrium. For some solutes and solvents there may be no such limit, in which case the two substances are said to be "miscible in all proportions" (or just "miscible").^[2]

The solute can be a solid, a liquid, or a gas, while the solvent is usually solid or liquid. Both may be pure substances, or may themselves be solutions. Gases are always miscible in all proportions, except in very extreme situations,^[3] and a solid or liquid can be "dissolved" in a gas only by passing into the gaseous state first.

The solubility mainly depends on the composition of solute and solvent (including their pH and the presence of other dissolved substances) as well as on temperature and pressure. The dependency can often be explained in terms of interactions between the particles (atoms, molecules, or ions) of the two substances, and of thermodynamic concepts such as enthalpy and entropy.

Under certain conditions, the concentration of the solute can exceed its usual solubility limit. The result is a supersaturated solution, which is metastable and will rapidly exclude the excess solute if a suitable nucleation site appears.^[4]

The concept of solubility does not apply when there is an irreversible chemical reaction between the two substances, such as the reaction of calcium hydroxide with hydrochloric acid; even though one might say, informally, that one "dissolved" the other. The solubility is also not the same as the rate of solution, which is how fast a solid solute dissolves in a liquid solvent. This property depends on many other variables, such as the physical form of the two substances and the manner and intensity of mixing.

The concept and measure of solubility are extremely important in many sciences besides chemistry, such as geology, biology, physics, and oceanography, as well as in engineering, medicine, agriculture, and even in non-technical activities like painting, cleaning, cooking, and brewing. Most chemical reactions of scientific, industrial, or practical interest only happen after the reagents have been dissolved in a suitable solvent. Water is by far the most common such solvent.

The term "soluble" is sometimes used for materials that can form colloidal suspensions of very fine solid particles in a liquid.^[5] The quantitative solubility of such substances is generally not well-defined, however.

The solubility of a specific solute in a specific solvent is generally expressed as the concentration of a saturated solution of the two.^[1] Any of the several ways of expressing concentration of solutions can be used, such as the mass, volume, or amount in moles of the solute for a specific mass, volume, or mole amount of the solvent or of the solution.

In particular, chemical handbooks will often express the solubility of a substance in a liquid as grams of solute per decilitre (100 mL) of solvent (g/dL); or, less commonly, as grams per litre (g/L). The quantity of solvent can instead be expressed in mass, as in g/100g" or g/kg. The number may be expressed as a percentage in this case, and the abbreviation "w/w" may be used to indicate "weight per weight".^[6] (The values in g/L and g/kg are practically the same for water, but not for other solvents.)

Alternatively, the quantity of solute can be expressed in moles instead of mass; if the quantity of solvent is given in kilograms, the value is the molality of the solution (mol/kg).

The solubility of a substance in a liquid may also be expressed as the quantity of solute per quantity of solution, rather than of solvent. For example, following the common practice in titration, it may be expressed as moles of solute per litre of solution (mol/L), the molarity of the latter.

In more specialized contexts the solubility may be given by the mole fraction (moles of solute per total moles of solute plus solvent) or by the mass fraction at equilibrium (mass of solute per mass of solute plus solvent), both adimensional numbers between 0 and 1 which may be expressed as percentages.

For solutions of liquids or gases in liquids, the quantities of both substances may be given volume rather than mass or mole amount; such as litre of solute per litre of solvent, or litre of solute per litre of solution. The value may be given as a percentage, and the abbreviation "v/v" for "volume per volume" may be used to indicate this choice.

Conversion between these various ways of measuring solubility may not be trivial, since it may require knowing the density of the solution — which is often not measured, and cannot be predicted. While the total mass is conserved by dissolution, the final volume may be different from both the volume of the solvent and the sum of the two volumes.^[7]

Moreover, many solids (such as acids and salts) will dissociate in non-trivial ways when dissolved; conversely, the solvent may form coordination complexes with the molecules or ions of the solute. In those cases, the sum of the moles of molecules of solute and solvent is not really the total moles of independent particles solution. To sidestep that problem, the solubility per mole of solution is usually computed and quoted as if the solute does not dissociate or form complexes -- that is, by pretending that the mole amount of solution is the sum of the mole amounts of the two substances.

The extent of solubility ranges widely, from infinitely soluble (without limit, i. e. miscible^[2]) such as ethanol in water, to essentially insoluble, such as titanium dioxide in water. A number of other descriptive terms are also used to qualify the extent of solubility for a given application. For example, U.S. Pharmacopoeia gives the following terms, according to the mass m_sv of solvent required to dissolve one unit of mass m_su of solute:^[8] (The solubilities of the examples are approximate, for water at 20-25 °C.)

The thresholds to describe something as insoluble, or similar terms, may depend on the application. For example, one source states that substances are described as "insoluble" when their solubility is less than 0.1 g per 100 mL of solvent.^[9]

Solubility occurs under dynamic equilibrium, which means that solubility results from the simultaneous and opposing processes of dissolution and phase joining (e.g. precipitation of solids). The solubility equilibrium occurs when the two processes proceed at equal and opposite rates.

The term solubility is also used in some fields where the solute is altered by solvolysis. For example, many metals and their oxides are said to be "soluble in hydrochloric acid", although in fact the aqueous acid irreversibly degrades the solid to give soluble products. It is also true that most ionic solids are dissolved by polar solvents, but such processes are reversible. In those cases where the solute is not recovered upon evaporation of the solvent, the process is referred to as solvolysis. The thermodynamic concept of solubility does not apply straightforwardly to solvolysis.

When a solute dissolves, it may form several species in the solution. For example, an aqueous suspension of ferrous hydroxide, Fe(OH)2, will contain the series [Fe(H2O)x(OH)x](2x)+ as well as other species. Furthermore, the solubility of ferrous hydroxide and the composition of its soluble components depend on pH. In general, solubility in the solvent phase can be given only for a specific solute that is thermodynamically stable, and the value of the solubility will include all the species in the solution (in the example above, all the iron-containing complexes).

Solubility is defined for specific phases. For example, the solubility of aragonite and calcite in water are expected to differ, even though they are both polymorphs of calcium carbonate and have the same chemical formula.

The solubility of one substance in another is determined by the balance of intermolecular forces between the solvent and solute, and the entropy change that accompanies the solvation. Factors such as temperature and pressure will alter this balance, thus changing the solubility.

Solubility may also strongly depend on the presence of other species dissolved in the solvent, for example, complex-forming anions (ligands) in liquids. Solubility will also depend on the excess or deficiency of a common ion in the solution, a phenomenon known as the common-ion effect. To a lesser extent, solubility will depend on the ionic strength of solutions. The last two effects can be quantified using the equation for solubility equilibrium.

For a solid that dissolves in a redox reaction, solubility is expected to depend on the potential (within the range of potentials under which the solid remains the thermodynamically stable phase). For example, solubility of gold in high-temperature water is observed to be almost an order of magnitude higher (i.e. about ten times higher) when the redox potential is controlled using a highly oxidizing Fe₃O₄-Fe₂O₃ redox buffer than with a moderately oxidizing Ni-NiO buffer.^[10]

Solubility (metastable, at concentrations approaching saturation) also depends on the physical size of the crystal or droplet of solute (or, strictly speaking, on the specific surface area or molar surface area of the solute).^[11] For quantification, see the equation in the article on solubility equilibrium. For highly defective crystals, solubility may increase with the increasing degree of disorder. Both of these effects occur because of the dependence of solubility constant on the Gibbs energy of the crystal. The last two effects, although often difficult to measure, are of practical importance.^{[citation needed]} For example, they provide the driving force for precipitate aging (the crystal size spontaneously increasing with time).

The solubility of a given solute in a given solvent is function of temperature. Depending on the change in enthalpy (ΔH) of the dissolution reaction, i.e., on the endothermic (ΔH > 0) or exothermic (ΔH < 0) character of the dissolution reaction, the solubility of a given compound may increase or decrease with temperature. The van 't Hoff equation relates the change of solubility equilibrium constant (K_sp) to temperature change and to reaction enthalpy change. For most solids and liquids, their solubility increases with temperature because their dissolution reaction is endothermic (ΔH > 0).^[12] In liquid water at high temperatures, (e.g. that approaching the critical temperature), the solubility of ionic solutes tends to decrease due to the change of properties and structure of liquid water; the lower dielectric constant results in a less polar solvent and in a change of hydration energy affecting the ΔG of the dissolution reaction.

Gaseous solutes exhibit more complex behavior with temperature. As the temperature is raised, gases usually become less soluble in water (exothermic dissolution reaction related to their hydration) (to a minimum, which is below 120 °C for most permanent gases^[13]), but more soluble in organic solvents (endothermic dissolution reaction related to their solvation).^[12]

The chart shows solubility curves for some typical solid inorganic salts in liquid water (temperature is in degrees Celsius, i.e. kelvins minus 273.15).^[14] Many salts behave like barium nitrate and disodium hydrogen arsenate, and show a large increase in solubility with temperature (ΔH > 0). Some solutes (e.g. sodium chloride in water) exhibit solubility that is fairly independent of temperature (ΔH ≈ 0). A few, such as calcium sulfate (gypsum) and cerium(III) sulfate, become less soluble in water as temperature increases (ΔH < 0).^[15] This is also the case for calcium hydroxide (portlandite), whose solubility at 70 °C is about half of its value at 25 °C. The dissolution of calcium hydroxide in water is also an exothermic process (ΔH < 0) and obeys the van 't Hoff equation and Le Chatelier's principle. A lowering of temperature favors the removal of dissolution heat from the system and thus favors dissolution of Ca(OH)₂: so portlandite solubility increases at low temperature. This temperature dependence is sometimes referred to as "retrograde" or "inverse" solubility. Occasionally, a more complex pattern is observed, as with sodium sulfate, where the less soluble decahydrate crystal (mirabilite) loses water of crystallization at 32 °C to form a more soluble anhydrous phase (thenardite) with a smaller change in Gibbs free energy (ΔG) in the dissolution reaction.^{[citation needed]}

The solubility of organic compounds nearly always increases with temperature. The technique of recrystallization, used for purification of solids, depends on a solute's different solubilities in hot and cold solvent. A few exceptions exist, such as certain cyclodextrins.^[16]

For condensed phases (solids and liquids), the pressure dependence of solubility is typically weak and usually neglected in practice. Assuming an ideal solution, the dependence can be quantified as:

where the index i {\displaystyle i} iterates the components, N i {\displaystyle N_{i}} is the mole fraction of the i {\displaystyle i} -th component in the solution, P {\displaystyle P} is the pressure, the index T {\displaystyle T} refers to constant temperature, V i , a q {\displaystyle V_{i,aq}} is the partial molar volume of the i {\displaystyle i} -th component in the solution, V i , c r {\displaystyle V_{i,cr}} is the partial molar volume of the i {\displaystyle i} -th component in the dissolving solid, and R {\displaystyle R} is the universal gas constant.^[17]

The pressure dependence of solubility does occasionally have practical significance. For example, precipitation fouling of oil fields and wells by calcium sulfate (which decreases its solubility with decreasing pressure) can result in decreased productivity with time.

Henry's law is used to quantify the solubility of gases in solvents. The solubility of a gas in a solvent is directly proportional to the partial pressure of that gas above the solvent. This relationship is similar to Raoult's law and can be written as:

where k H {\displaystyle k_{\rm {H}}} is a temperature-dependent constant (for example, 769.2 L·atm/mol for dioxygen (O₂) in water at 298 K), p {\displaystyle p} is the partial pressure (in atm), and c {\displaystyle c} is the concentration of the dissolved gas in the liquid (in mol/L).

The solubility of gases is sometimes also quantified using Bunsen solubility coefficient.

In the presence of small bubbles, the solubility of the gas does not depend on the bubble radius in any other way than through the effect of the radius on pressure (i.e. the solubility of gas in the liquid in contact with small bubbles is increased due to pressure increase by Δp = 2γ/r; see Young–Laplace equation).^[18]

Henry's law is valid for gases that do not undergo change of chemical speciation on dissolution. Sieverts' law shows a case when this assumption does not hold.

The carbon dioxide solubility in seawater is also affected by temperature, pH of the solution, and by the carbonate buffer. The decrease of solubility of carbon dioxide in seawater when temperature increases is also an important retroaction factor (positive feedback) exacerbating past and future climate changes as observed in ice cores from the Vostok site in Antarctica. At the geological time scale, because of the Milankovich cycles, when the astronomical parameters of the Earth orbit and its rotation axis progressively change and modify the solar irradiance at the Earth surface, temperature starts to increase. When a deglaciation period is initiated, the progressive warming of the oceans releases CO₂ into the atmosphere because of its lower solubility in warmer sea water. In turn, higher levels of CO₂ in the atmosphere increase the greenhouse effect and carbon dioxide acts as an amplifier of the general warming.

A popular aphorism used for predicting solubility is "like dissolves like" also expressed in the Latin language as "Similia similibus solventur".^[19] This statement indicates that a solute will dissolve best in a solvent that has a similar chemical structure to itself, based on favorable entropy of mixing. This view is simplistic, but it is a useful rule of thumb. The overall solvation capacity of a solvent depends primarily on its polarity.^[a] For example, a very polar (hydrophilic) solute such as urea is very soluble in highly polar water, less soluble in fairly polar methanol, and practically insoluble in non-polar solvents such as benzene. In contrast, a non-polar or lipophilic solute such as naphthalene is insoluble in water, fairly soluble in methanol, and highly soluble in non-polar benzene.^[20]

In even more simple terms a simple ionic compound (with positive and negative ions) such as sodium chloride (common salt) is easily soluble in a highly polar solvent (with some separation of positive (δ+) and negative (δ-) charges in the covalent molecule) such as water, as thus the sea is salty as it accumulates dissolved salts since early geological ages.

The solubility is favored by entropy of mixing (ΔS) and depends on enthalpy of dissolution (ΔH) and the hydrophobic effect. The free energy of dissolution (Gibbs energy) depends on temperature and is given by the relationship: ΔG = ΔH – TΔS. Smaller ΔG means greater solubility.

Chemists often exploit differences in solubilities to separate and purify compounds from reaction mixtures, using the technique of liquid-liquid extraction. This applies in vast areas of chemistry from drug synthesis to spent nuclear fuel reprocessing.

Dissolution is not an instantaneous process. The rate of solubilization (in kg/s) is related to the solubility product and the surface area of the material. The speed at which a solid dissolves may depend on its crystallinity or lack thereof in the case of amorphous solids and the surface area (crystallite size) and the presence of polymorphism. Many practical systems illustrate this effect, for example in designing methods for controlled drug delivery. In some cases, solubility equilibria can take a long time to establish (hours, days, months, or many years; depending on the nature of the solute and other factors).

The rate of dissolution can be often expressed by the Noyes–Whitney equation or the Nernst and Brunner equation^[21] of the form:

For dissolution limited by diffusion (or mass transfer if mixing is present), C s {\displaystyle C_{s}} is equal to the solubility of the substance. When the dissolution rate of a pure substance is normalized to the surface area of the solid (which usually changes with time during the dissolution process), then it is expressed in kg/m²s and referred to as "intrinsic dissolution rate". The intrinsic dissolution rate is defined by the United States Pharmacopeia.

Dissolution rates vary by orders of magnitude between different systems. Typically, very low dissolution rates parallel low solubilities, and substances with high solubilities exhibit high dissolution rates, as suggested by the Noyes-Whitney equation.

Solubility constants are used to describe saturated solutions of ionic compounds of relatively low solubility (see solubility equilibrium). The solubility constant is a special case of an equilibrium constant. Since it is a product of ion concentrations in equilibrium, it is also known as the solubility product. It describes the balance between dissolved ions from the salt and undissolved salt. The solubility constant is also "applicable" (i.e. useful) to precipitation, the reverse of the dissolving reaction. As with other equilibrium constants, temperature can affect the numerical value of solubility constant. While the solubility constant is not as simple as solubility, the value of this constant is generally independent of the presence of other species in the solvent.

The Flory–Huggins solution theory is a theoretical model describing the solubility of polymers. The Hansen solubility parameters and the Hildebrand solubility parameters are empirical methods for the prediction of solubility. It is also possible to predict solubility from other physical constants such as the enthalpy of fusion.

The octanol-water partition coefficient, usually expressed as its logarithm (Log P), is a measure of differential solubility of a compound in a hydrophobic solvent (1-octanol) and a hydrophilic solvent (water). The logarithm of these two values enables compounds to be ranked in terms of hydrophilicity (or hydrophobicity).

The energy change associated with dissolving is usually given per mole of solute as the enthalpy of solution.

Solubility is of fundamental importance in a large number of scientific disciplines and practical applications, ranging from ore processing and nuclear reprocessing to the use of medicines, and the transport of pollutants.

Solubility is often said to be one of the "characteristic properties of a substance", which means that solubility is commonly used to describe the substance, to indicate a substance's polarity, to help to distinguish it from other substances, and as a guide to applications of the substance. For example, indigo is described as "insoluble in water, alcohol, or ether but soluble in chloroform, nitrobenzene, or concentrated sulfuric acid".^{[citation needed]}

Solubility of a substance is useful when separating mixtures. For example, a mixture of salt (sodium chloride) and silica may be separated by dissolving the salt in water, and filtering off the undissolved silica. The synthesis of chemical compounds, by the milligram in a laboratory, or by the ton in industry, both make use of the relative solubilities of the desired product, as well as unreacted starting materials, byproducts, and side products to achieve separation.

Another example of this is the synthesis of benzoic acid from phenylmagnesium bromide and dry ice. Benzoic acid is more soluble in an organic solvent such as dichloromethane or diethyl ether, and when shaken with this organic solvent in a separatory funnel, will preferentially dissolve in the organic layer. The other reaction products, including the magnesium bromide, will remain in the aqueous layer, clearly showing that separation based on solubility is achieved. This process, known as liquid–liquid extraction, is an important technique in synthetic chemistry. Recycling is used to ensure maximum extraction.

In flowing systems, differences in solubility often determine the dissolution-precipitation driven transport of species. This happens when different parts of the system experience different conditions. Even slightly different conditions can result in significant effects, given sufficient time.

For example, relatively low solubility compounds are found to be soluble in more extreme environments, resulting in geochemical and geological effects of the activity of hydrothermal fluids in the Earth's crust. These are often the source of high quality economic mineral deposits and precious or semi-precious gems. In the same way, compounds with low solubility will dissolve over extended time (geological time), resulting in significant effects such as extensive cave systems or Karstic land surfaces.

Some ionic compounds (salts) dissolve in water, which arises because of the attraction between positive and negative charges (see: solvation). For example, the salt's positive ions (e.g. Ag⁺) attract the partially negative oxygen atom in H2O. Likewise, the salt's negative ions (e.g. Cl⁻) attract the partially positive hydrogens in H2O. Note: the oxygen atom is partially negative because it is more electronegative than hydrogen, and vice versa (see: chemical polarity).

However, there is a limit to how much salt can be dissolved in a given volume of water. This concentration is the solubility and related to the solubility product, K_sp. This equilibrium constant depends on the type of salt (AgCl vs. NaCl, for example), temperature, and the common ion effect.

One can calculate the amount of AgCl that will dissolve in 1 liter of pure water as follows:

[Ag⁺] = [Cl⁻], in the absence of other silver or chloride salts, so

The result: 1 liter of water can dissolve 1.34 × 10⁻⁵ moles of AgCl at room temperature. Compared with other salts, AgCl is poorly soluble in water. For instance, table salt (NaCl) has a much higher K_sp = 36 and is, therefore, more soluble. The following table gives an overview of solubility rules for various ionic compounds.

The principle outlined above under polarity, that like dissolves like, is the usual guide to solubility with organic systems. For example, petroleum jelly will dissolve in gasoline because both petroleum jelly and gasoline are non-polar hydrocarbons. It will not, on the other hand, dissolve in ethyl alcohol or water, since the polarity of these solvents is too high. Sugar will not dissolve in gasoline, since sugar is too polar in comparison with gasoline. A mixture of gasoline and sugar can therefore be separated by filtration or extraction with water.

This term is often used in the field of metallurgy to refer to the extent that an alloying element will dissolve into the base metal without forming a separate phase. The solvus or solubility line (or curve) is the line (or lines) on a phase diagram that give the limits of solute addition. That is, the lines show the maximum amount of a component that can be added to another component and still be in solid solution. In the solid's crystalline structure, the 'solute' element can either take the place of the matrix within the lattice (a substitutional position; for example, chromium in iron) or take a place in a space between the lattice points (an interstitial position; for example, carbon in iron).

In microelectronic fabrication, solid solubility refers to the maximum concentration of impurities one can place into the substrate.

In solid compounds (as opposed to elements), the solubility of a solute element can also depend on the phases separating out in equilibrium. For example, amount of Sn soluble in the ZnSb phase can depend significantly on whether the phases separating out in equilibrium are (Zn₄Sb₃+Sn(L)) or (ZnSnSb₂+Sn(L))^[23]. Besides these, the ZnSb compound with Sn as a solute can separate out into other combinations of phases after the solubility limit is reached depending on the initial chemical composition during synthesis. Each combination produces a different solubility of Sn in ZnSb. Hence solubility studies in compounds, concluded upon the first instance of observing secondary phases separating out might underestimate solubility.^[24] While the maximum number of phases separating out at once in equilibrium can be determined by the Gibb's phase rule, for chemical compounds there is no limit on the number of such phase separating combinations itself. Hence, establishing the "maximum solubility" in solid compounds experimentally can be difficult, requiring equilibration of many samples. If the dominant crystallographic defect (mostly interstitial or substitutional point defects) involved in the solid-solution can be chemically intuited beforehand, then using some simple thermodynamic guidelines can considerably reduce the number of samples required to establish maximum solubility. ^[25]

Many substances dissolve congruently (i.e. the composition of the solid and the dissolved solute stoichiometrically match). However, some substances may dissolve incongruently, whereby the composition of the solute in solution does not match that of the solid. This solubilization is accompanied by alteration of the "primary solid" and possibly formation of a secondary solid phase. However, in general, some primary solid also remains and a complex solubility equilibrium establishes. For example, dissolution of albite may result in formation of gibbsite.^[26]

In this case, the solubility of albite is expected to depend on the solid-to-solvent ratio. This kind of solubility is of great importance in geology, where it results in formation of metamorphic rocks.

In principle, both congruent and incongruent dissolution can lead to the formation of secondary solid phases in equilibrium. So, in the field of Materials Science, the solubility for both cases is described more generally on chemical composition phase diagrams.

Solubility is a property of interest in many aspects of science, including but not limited to: environmental predictions, biochemistry, pharmacy, drug-design, agrochemical design, and protein ligand binding. Aqueous solubility is of fundamental interest owing to the vital biological and transportation functions played by water.^[27][28][29] In addition, to this clear scientific interest in water solubility and solvent effects; accurate predictions of solubility are important industrially. The ability to accurately predict a molecule's solubility represents potentially large financial savings in many chemical product development processes, such as pharmaceuticals.^[30] In the pharmaceutical industry, solubility predictions form part of the early stage lead optimisation process of drug candidates. Solubility remains a concern all the way to formulation.^[30] A number of methods have been applied to such predictions including quantitative structure–activity relationships (QSAR), quantitative structure–property relationships (QSPR) and data mining. These models provide efficient predictions of solubility and represent the current standard. The draw back such models is that they can lack physical insight. A method founded in physical theory, capable of achieving similar levels of accuracy at an sensible cost, would be a powerful tool scientifically and industrially.^{[31][32][33][34]}

Methods founded in physical theory tend to use thermodynamic cycles, a concept from classical thermodynamics. The two common thermodynamic cycles used involve either the calculation of the free energy of sublimation (solid to gas without going through a liquid state) and the free energy of solvating a gaseous molecule (gas to solution), or the free energy of fusion (solid to a molten phase) and the free energy of mixing (molten to solution). These two process are represented in the following diagrams.

These cycles have been used for attempts at first principles predictions (solving using the fundamental physical equations) using physically motivated solvent models,^[32] to create parametric equations and QSPR models^[35][33] and combinations of the two.^[33] The use of these cycles enables the calculation of the solvation free energy indirectly via either gas (in the sublimation cycle) or a melt (fusion cycle). This is helpful as calculating the free energy of solvation directly is extremely difficult. The free energy of solvation can be converted to a solubility value using various formulae, the most general case being shown below, where the numerator is the free energy of solvation, R is the gas constant and T is the temperature in kelvins.^[32]

Well known fitted equations for solubility prediction are the general solubility equations. These equations stem from the work of Yalkowsky et al.^[36][37] The original formula is given first, followed by a revised formula which takes a different assumption of complete miscibility in octanol.^[37]

These equations are founded on the principles of the fusion cycle.

La solubilidad es la cantidad maxima de soluto que puede ser disuelto en un solvente en equilibrio, conformando asi una solucion saturada.

Las sustancias solubles son aquellas que al entrar en contacto con otro liquido se disuelven y forman una solucion. La sustancia que se disuelve es el soluto y la sustancia en la que se disuelve es el solvente. La solucion es la mezcla entre soluto y solvente.

Soluto y solvente pueden presentarse en estado liquido, solido y gaseoso. Estos materiales o sustancias intercambian electrones al entrar en contacto en las proporciones adecuadas; esto da lugar a la formacion de nuevos compuestos.

El solvente universal es el agua; sin embargo, no todos los materiales o sustancias son solubles en este.

1- Sal: o cloruro de sodio, es ordinariamente soluble en agua a 20 °C.

2- Azucar: es ordinariamente soluble en agua a 20 °C.

3- Gelatina: es soluble en agua en presencia de calor.

4- Jugos en polvo: mezcla de azucar, saborizantes y conservantes, ordinariamente solubles en agua a 20 °C.

5- Los nitratos: estan comunmente presentes en los fertilizantes empleados en la agricultura.

6- Alcohol: tanto etilico como isopropilico.

7- Vino: es una mezcla de alcohol y fruta fermentada.

8- Jabon: por poseer carbono, hidrogeno y sal en su composicion, se disuelve al entrar en contacto con el agua.

9- Amoniaco: existe en la amplia gama de productos de limpieza domestica.

10- Oxigeno: este gas disuelto en agua es el que respiran los animales acuaticos.

11- Vinagre: al ser acido y polar, este se disuelve facilmente en el agua.

12- Sacarina: es un edulcorante puede disolverse en el agua a 22 oC .

13- Aspartamo: es un edulcorante que se disuelve con dificultad en el agua a 20 oC.

14- Bicarbonato de sodio: compuesto solido de facil solubilidad en el agua. 

15- Mayonesa: es una mezcla de huevo, vinagre y sal en aceite.

16- Pinturas, lacas y tintes: se disuelven en thinner, acetona o metiletilcetona.

17- Barniz de unas: se disuelve en thinner o acetona.

18- Plastico: reacciona ante disolventes organicos a base de etilenglicol.

19- Pegamento: se disuelve en formol.

20- Aceites y ceras: en dietileter, tambien llamado eter etilico.

21- Resinas y gomas: disueltos en tolueno.

22- Caucho y cuero: pueden disolverse en xileno.

23- Grasas: logran disolverse en metanol.

24- Amalgama dental de oro: es oro disuelto en mercurio.

25- Cafe o cacao: pueden disolverse en leche, siendo la tasa mayor segun a la temperatura que esten los componentes.

La polaridad es el elemento que define si la sustancia es soluble en agua o no. La mayoria de las reacciones quimicas cotidianas e importantes de la vida se llevan a cabo en un ambiente acuoso. 

La polaridad se refiere a aquellas moleculas que no estan compuestas por iones, y presentan exceso de carga positiva en uno de sus extremos y de carga negativa en el otro. 

El agua, gracias a su polaridad y a su propiedad de formacion de puentes de hidrogeno, puede disolver iones y moleculas de diversos tipos, siempre y cuando estos sean polares.

En el caso de las moleculas no polares, como las grasas, los plasticos y los aceites, el agua no actua como solvente, al punto que cuando se intentan mezclar ambas sustancias no se disuelven sino que permanecen separadas en forma de capas.

Este tipo de moleculas no polares se disuelven en sustancias como el eter, la nafta, el benceno, el thinner y la acetona, entre otros similares.

Humanity has been trying to solve this problem every morning for a thousand years.

Nature imprisons thousands of tasty solubles inside of coffee beans, and we want them in our cup.

Over time we've learned that pouring hot water onto coffee grounds turns the water into coffee. 

Sometimes it tastes good, and sometimes it is not so good. Why is that?

We will attempt to answer that question by zooming down to the microscopic level inside of a coffee bean and looking to see what happens when coffee grounds and water meet. 

When we look at coffee from the cellular level, it is easy to understand how the ratio of water to coffee, time and grind size impact the brewing process. This will help us build a intuitive sense for thinking about concepts like Extraction and Total Dissolved Solids (TDS).

There is no need to fear these abstract concepts or expect a story filled with mundane technical details. The story we discover is one of an epic prison break where millions of good guys find freedom and the bad guys are left behind bars. And as you might expect, there is a superhero that saves the day.

Our journey starts with a single arabica coffee bean. If we were to think of this coffee bean as a prison, it would have over 4,500,000 cells! Now imagine cutting a horizontal slice right through the middle of the bean in the image above.

This view is looking down at the cross section of a roasted coffee bean that has been cut in half. Notice all of the tiny holes in the bean. Each one of those holes used to be a living cell when the coffee bean was growing inside of a cherry on a coffee tree. 

This view has been magnified 750X with an electron microscope so we can easily see each individual cell. The width of one of these cells is about half the thickness of one of the hairs on your head. (50 - 70 microns)

When the coffee bean is roasted, the cells fill with CO2 gas and expand. Trapped within the walls of each cell are solubles that we want to release into our coffee.

"Solubles" is the overarching term that is used for the substances in a coffee bean that can be dissolved by water. At the most basic level, brewing coffee is using water as a solvent to dissolve the solubles that are locked in the cells of a coffee bean.

Solubles come in many different shapes and sizes. The image above describes the four main categories found in coffee beans and the unique flavor notes each one contributes to the taste of coffee.

Fruit acids and caffeine are the easiest to dissolve and are responsible for light and fruity flavor notes.

Lipids are the natural fats and oils found in coffee beans. They aren't technically soluble in water but water can still release them from the coffee cell as an emulsion.

Brewing methods that use metal filters like French Press and espresso allow lipids to pass through into the cup, producing the mouthfeel those methods are known for.

The pores in paper filters are so small that they prevent most lipids from passing through. Drip brewing methods like pour over will only contain 1/10th the lipid content compared methods that use a metal filter.

When coffee is roasted, the Malliard reaction produces melanoidins that are responsible for the browning color of coffee, both in bean and liquid form.

Carbohydrates make up 50% of a dry coffee beans total mass yet only some of the carbohydrates are soluble. Their main role is to add sweetness and earthy flavors.

As the coffee cherry develops on the tree, Mother Nature locks these innocent solubles inside the cells of each coffee bean.

We're back inside the coffee bean and it's not looking good for the solubles. After the bean has developed, been picked, processed and roasted the solubles are locked up inside of dark cells. At least it probably smells good inside. 

*Note, the colored balls are used as a representation of the solubles and are not drawn to scale.

Water is here to save the day! When water enters the coffee cells it begins dissolving the solubles. This new solution of solubles dissolved in water is known as coffee.

When we look at the total mass of a coffee bean, only 30% of it consists of solubles. The other 70% of the bean is made of insoluble fibers and carbohydrates that create the beans structure.

About 20% of the bean contains good solubles and the other 10% are bad and taste awful. To brew the best cup of coffee we have to try and release the good solubles while leaving the bad ones locked up in the cells.

Luckily the bad solubles move slower and take longer to dissolve than the good solubles so we can coordinate the jailbreak by limiting amount of time water has to work.

In the coffee world, extraction rate is the term used to quantify how many of the solubles should remain locked up in the Coffea Arabica Prision cell and how many we want to free.

The longer that water is in a cell, the more solubles are able to be dissolved.

The optimal guidelines set by the SCAA for extraction are 18 - 22%. So this means that when we take the total weight of our coffee beans, 18-22% of that mass will be dissolved by water and end up in our cup.

Now that we know how water interacts with each cell individually we can look at how it will interact with the entire bean. To simplify, we are going to look at the cells as if they were in a 2D or flat environment. In reality the bean is a 3D structure but the concepts transfer easily.

In the image above imagine that the entire bean was placed into water. The water would only be able to access the cells on the outer surface of the bean, represented by the blue highlight.

Our goal is to free the solubles throughout the entire bean so we need to find a way for the water to access the inner cells.

We can increase the number of cells that water can access by breaking the bean into smaller pieces. As the pieces get smaller the total number of cells that water can contact increases exponentially.

Think of the boxes above as a single coffee ground with 30 cells by 30 cells. In the first box water has been in contact with the coffee ground for 30 seconds. In this time water was able to enter the first two cells on the outer edge of the coffee ground and carry out the solubles inside of them.

After 120 seconds the water has made it through 15 cells. If you were to stop the brewing process at this point the solubles that are in cells at the center of the coffee ground would still be trapped there. This would be considered an under extracted coffee ground.

After 240 seconds water has worked its way into all of the cells and the coffee particle is fully extracted.

Now consider what happens when we change the grind size. The time scales of 30, 120 and 240 seconds are the same, and the total number of cells is the same. 

Yet it is now possible to fully extract the same number of cells in 30 seconds as 240 seconds.

Grind size doesn't determine what is being extracted, it determines how long it will take for the water to reach all of the cells.

Hopefully it is starting to become clear how time and grind size are inversely linked. When we increase one, we must decrease the other.

What if we use different grind sizes but keep a time of 120 seconds for all sizes?

Recall from earlier that it is possible to over extract a cell and release some of the bad solubles if water is left in contact with it for too long. The orange cells in the box on the left represent cells that were over extracted.

The middle represents our optimum extraction of 20%. The time and grind size are in the right balance where water has just enough time to dissolve the good solubles and leave the bad ones locked up.

There wasn't enough time for water to access all of the cells for the box on the right so both of the good and bad solubles remained locked inside the center of the coffee ground.

We can now see why it is important to have a consistent particle size when we grind coffee beans into smaller pieces. If the grind is inconsistent it will cause some of the grounds to be over extracted while others are under extracted.

Until this point everything has been about extraction, the balance of good and bad solubles that are released from each cell. Now lets look at strength, also known as Total Dissolved Solids (TDS).

TDS can be simply defined as the ratio of solubles to water in a cup. This is largely a matter of personal preference but it is generally considered that 1.15% to 1.35% is an optimal ratio.

This means that for every 1 soluble we have 99 parts water.

The solubles released during extraction determine the flavor and TDS determines the intensity of those flavors. This is similar to music if you think of solubles as the music itself and TDS is how loud the volume is set.

Increasing TDS will produce a stronger flavor but turning it up too high may cause some flavors to over power others completely.

Extraction and TDS are the two ratios that define coffee brewing. Hopefully this story has helped develop an intuitive understanding of what is happening when coffee grounds steep in water and why small changes in the ratios can lead to big differences in flavor.

You now have the tools to dial in your brewing recipe and get the best flavor out of our coffee beans. The only thing left to do is to start experimenting and free some solubles!

La solubilidad es la capacidad de una sustancia de disolverse en otra llamada disolvente.^[1]​ Tambien hace referencia a la masa de soluto que se puede disolver en determinada masa de disolvente, en ciertas condiciones de temperatura, e incluso presion (en caso de un soluto gaseoso). La solubilidad la podemos encontrar en diferentes mezclas como por ejemplo en el ion comun es muy dificil encontrar ya que el ion comun es principal en la solubilidad. Si en una disolucion no se puede disolver mas soluto se dice que la disolucion esta saturada. Bajo ciertas condiciones la solubilidad puede sobrepasar ese maximo y pasa a denominarse solucion sobresaturada.^[2]​Por el contrario, si la disolucion admite aun mas soluto, se dice que se encuentra insaturada.

No todas las sustancias se disuelven en un mismo solvente. Por ejemplo, en el agua, se disuelve el alcohol y la sal, en tanto que el aceite y la gasolina no se disuelven en agua. En la solubilidad, el caracter polar o apolar de la sustancia influye mucho, ya que, debido a este caracter, la sustancia sera mas o menos soluble; por ejemplo, los compuestos con mas de un grupo funcional presentan gran polaridad por lo que no son solubles en eter etilico. Los compuestos poco reactivos, como las parafinas, compuestos aromaticos y los derivados halogenados tienen menor solubilidad.

El termino solubilidad se utiliza tanto para designar al fenomeno cualitativo del proceso de disolucion como para expresar cuantitativamente la concentracion de las soluciones. La solubilidad de una sustancia depende de la naturaleza del solvente y del soluto, asi como de la temperatura y la presion del sistema.

La solubilidad se define para fases especificas. Por ejemplo, la solubilidad de aragonito y calcita en el agua se espera que difieran, si bien ambos son polimorfos de carbonato de calcio y tienen la misma formula molecular.

La solubilidad de una sustancia en otra esta determinada por el equilibrio de fuerzas intermoleculares entre el solvente y el soluto, y la variacion de entropia que acompana a la solvatacion. Factores como la temperatura y la presion influyen en este equilibrio, cambiando asi la solubilidad.

La solubilidad tambien depende en gran medida de la presencia de otras sustancias disueltas en el solvente como por ejemplo la existencia de complejos metalicos en los liquidos. La solubilidad dependera tambien del exceso o defecto de algun ion comun, con el soluto, en la solucion; tal fenomeno es conocido como el efecto del ion comun. En menor medida, la solubilidad dependera de la fuerza ionica de las soluciones. Los dos ultimos efectos mencionados pueden cuantificarse utilizando la ecuacion de equilibrio de solubilidad.

Para un solido que se disuelve en una reaccion redox, la solubilidad se espera que dependa de las posibilidades (dentro del alcance de los potenciales en las que el solido se mantiene la fase termodinamicamente estable). Por ejemplo, la solubilidad del oro en el agua a alta temperatura se observa que es casi de un orden de magnitud mas alta cuando el potencial redox se controla mediante un tampon altamente oxidante redox Fe₃O₄-Fe₂O₃ que con un tampon moderadamente oxidante Ni-NiO.^[3]​

La solubilidad (metaestable) tambien depende del tamano fisico del grano de cristal o mas estrictamente hablando, de la superficie especifica (o molar) del soluto. Para evaluar la cuantificacion, se debe ver la ecuacion en el articulo sobre el equilibrio de solubilidad. Para cristales altamente defectuosos en su estructura, la solubilidad puede aumentar con el aumento del grado de desorden. Ambos efectos se producen debido a la dependencia de la solubilidad constante frente a la denominada energia libre de Gibbs asociada con el cristal. Los dos ultimos efectos, aunque a menudo dificiles de medir, son de relevante importancia en la practica ^{[cita requerida]} pues proporcionan la fuerza motriz para determinar su grado de precipitacion, ya que el tamano de cristal crece de forma espontanea con el tiempo.

La solubilidad de un soluto en un determinado solvente principalmente depende de la temperatura. Para muchos solidos disueltos en el agua liquida, la solubilidad aumenta con la temperatura hasta 100 °C,^[4]​ aunque existen casos que presentan un comportamiento inverso. En la mayoria de los casos en el agua liquida a altas temperaturas la solubilidad de los solutos ionicos tiende a aumentar debido al cambio de las propiedades y la estructura del agua liquida, que reduce la constante dielectrica de un disolvente menos polar.

Los solutos gaseosos muestran un comportamiento mas complejo con la temperatura. Al elevarse la temperatura, los gases generalmente se vuelven menos solubles en agua (el minimo que esta por debajo de 120 °C para la mayoria de gases),^[5]​ pero mas solubles en solventes organicos.^[4]​

El grafico muestra las curvas de solubilidad de algunas sales solidas inorganicas tipicas.^[6]​ Muchas sales se comportan como el nitrato de bario y el arseniato acido disodico, y muestran un gran aumento de la solubilidad con la temperatura. Algunos solutos (por ejemplo, cloruro de sodio (NaCl) en agua) exhiben una solubilidad bastante independiente de la temperatura. Unos pocos, como el sulfato de cerio (III) y el carbonato de litio, se vuelven menos solubles en agua a medida que aumenta la temperatura. Esta dependencia de la temperatura se refiere a veces como «retrograda» o «solubilidad inversa». En ocasiones, se observa un patron mas complejo, como con sulfato de sodio, donde el cristal decahidratado menos soluble pierde agua de cristalizacion a 32 °C para formar una fase anhidra menos soluble. ^{[cita requerida]}

La solubilidad de los compuestos organicos casi siempre aumenta con la temperatura. La tecnica de la recristalizacion, utilizado para la purificacion de solidos, depende de un soluto de diferentes solubilidades en un solvente caliente y fria. Existen algunas excepciones, tales como determinadas ciclodextrinas.^[7]​

La solubilidad de los gases varia no solo con la temperatura sino ademas con la presion ejercida sobre el mismo. De esta manera, la cantidad de un soluto gaseoso que puede disolverse en un determinado solvente, aumenta al someterse a una presion parcial mayor (vease Ley de Henry). A nivel industrial, esto se puede observar en el envasado de bebidas gaseosas por ejemplo, donde se aumenta la solubilidad del dioxido de carbono ejerciendo una presion de alrededor de 4 atm. ^{[cita requerida]}

Una forma muy comun de encontrar los valores que describen cuantitativamente la solubilidad de un soluto es encontrar el maximo numero de gramos de soluto que pueden disolverse en una cantidad dada de solvente, teniendo esto en cuenta podemos expresar la solubilidad en moles por litro ( a esto se le conoce como solubilidad molar) solo si se sabe la masa molar de la sustancia. En el caso particular de las sales ionicas que son solo ligeramente solubles, se suele cuantificar su solubilidad mediante el estudio del siguiente equilibrio:^[8]​

MX ( s ) ↽ − − ⇀ M + ( ac ) + X − ( ac ) {\displaystyle {\ce {MX(s) <=>M+(ac) + X-(ac)}}}

cuando en un equilibrio participa alguna sustancia solida, la concentracion de esta no aparece en la expresion de la constante de equilibrio, ya que permanece constante. Esto ocurre con la concentracion de MX, por lo que la expresion queda :

K [ MX ] = Kps = [ M + ] [ X − ] {\displaystyle {\ce {K[MX] = Kps = [M+][X-]}}}

El producto de solubilidad de un compuesto ionico, es el producto de las concentraciones molares de los iones constituyentes, cada uno elevado a la potencia de su coeficiente estequiometrico en la ecuacion de equilibrio.

Corn condensed distillers solubles are a by-product of the ethanol production process. It is also known in the industry as “corn syrup.” It is a liquid by-product that contains fermentation by-products, spent yeast cells, and other nutrients which remain after corn grain has been fermented to produce ethanol. Generally, corn condensed distillers solubles are added back to the coarse grains during the process to produce wet or dry distillers grains with solubles. However, in some cases, corn condensed distillers solubles are sold as a separate by-product.

The nutrient content of corn condensed distillers solubles varies considerably from plant to plant and from day to day within a plant. Typical moisture content ranges from 55 to 80%. Levels of other nutrients also vary considerably. On a dry basis, CP ranges from 20 to 30%. Levels of phosphorus, potassium, and sulfur are also variable. Sulfur level is of particular concern since high sulfur levels have been implicated in increased incidence of polioencephalomalacia in cattle. Corn condensed distillers solubles contain moderate levels of fat, which gives the product energy values greater than corn on a dry basis.

Liquid handling equipment (tanks, pumps, hoses) are needed in order to handle this by-product. Because the product is high in moisture, it will freeze. Placing tanks and pumping equipment in a heated shop or shed or burying the tanks underground can alleviate this problem.

The nutrient profile of corn condensed distillers solubles makes it a useful supplement for beef cattle fed low-quality forage diets. Best results are obtained when the product is blended with chopped forage in a mixed ration, but the product can be fed separately as well. The amount needed as a supplement will vary but is typically less than 15% of the diet on a DM basis.

So, this entire post is referencing this SCAA chart, which shows the ideal measures of TDS (Solubles Concentration) and Extraction (Solubles Yield) for a good cup of coffee.

However, the "Solubles Concentration" and "Solubles Yield" terminology confuses me and I'm hoping someone can give me a better mental image of what's happening.

The "Solubles Concentration" (Y-Axis of chart) is a measure of the amount of coffee particles dissolved into the water -- right? Ideally, 1150 - 1350 TDS (parts per million), measured with a refractometer.

The "Solubles Yield" (X-Axis of Chart) is the percentage of coffee grind that makes it into your cup. It can be measured by drying out your cup of coffee in an oven and measuring the remaining coffee, OR via this formula: Extraction[%] = BrewedCoffee[total yield weight in grams] * TDS[%] / CoffeeGrounds[original beans weight in g]

I understand that these two measurements are responsible for very different things in the final taste of your coffee, but .. they sound like the exact same thing, measured in two different ways. Doesn't a higher concentration of solubles mean there will be a higher solubles yield, and vice versa? Isn't "the percentage of coffee in your final cup" just a different way of saying "the amount of coffee dissolved into water"?

Someone explain this like I'm 5! I can't wrap my head around this, and it's making it hard to get any deeper into the subject.

In epidemiologic studies, the association of vitamin C with cancer is mostly indirect, since it is based on the consumption of foods known to contain high or low concentrations of the vitamin rather than on measured ingestion of ascorbic acid.

Meinsma (1964) noted that the consumption of citrus fruits by persons with gastric cancer was lower than that by controls. Similar inverse associations between fresh fruit consumption or vitamin C intake and gastric cancer were reported by Bjelke (1978), Higginson (1966), Haenszel and Correa (1975), and Kolonel et al. (1981). In a case-control study of stomach cancer conducted in Canada, Risch et al. (1985) found that citrus fruit intake was somewhat protective (odds ratio 0.75 per 100 g daily average intake). In a univariate analysis, vitamin C intake was significantly (p = .0056) protective against stomach cancer. Risch and colleagues analyzed vitamin C intake from 21 common vegetables along with the intake of nitrate and found that vitamin C consumption had a strong and highly protective effect. In a multiple logistic regression model, however, vitamin C intake did not make a significant contribution to risk reduction beyond a protective effect found for dietary fiber. This could partly be explained by the correlation between the sources of vitamin C and dietary fiber.

Mettlin et al. (1981) found inverse associations of indices of vitamin A and vitamin C consumption with esophageal cancer based on frequency of consumption of selected food items by male cases and controls. The relationship was stronger for vitamin C than for vitamin A, and only the association with vitamin C was statistically significant after controlling for smoking and alcohol use.

In studies of esophageal cancer in the Caspian Littoral of Iran, inverse associations were found between esophageal cancer and consumption of fresh fruits and estimated vitamin C intake based on correlational and case-control data (Cook-Mozaffari, 1979; Cook-Mozaffari et al., 1979; Hormozdiari et al., 1975; Joint Iran-International Agency for Research on Cancer Study Group, 1977). In a study of diet and esophageal cancer conducted in the Calvados region of France, Tuyns et al. (1987b) found further evidence for a protective effect of vitamin C consumption as estimated from food data banks. The estimate of relative risk for moderate consumers of vitamin C was 0.7 and for heavy consumers, 0.4. Similar protective effects were also found for vitamin E, carotene, and some other micronutrients. It is not clear whether the results of this study reflect general nutritional deficiency, particularly in individuals with high alcohol consumption, or a more specific effect of vitamin C.

Jain et al. (1980) found no association between vitamin C consumption, also estimated from food data banks, and colon cancer in a case-control study in Canada. In a case-control study on colorectal cancer in Marseilles, Macquart-Moulin et al. (1986) found a significant protective effect of vitamin C after adjustment for age, caloric intake, and weight. The risk in the highest consumption category relative to the lowest was 0.16. In a multivariate analysis including other macro-and micronutrients, however, vitamin C was no longer significantly protective. The effect of vitamin C was also evaluated in two case-control studies of colorectal cancer in Australia. In one (Potter and McMichael, 1986), vitamin C consumption was associated with a reduced relative risk for rectal cancer in males and females (ages 30-74 years), especially for younger males; the effect disappeared by 70 years of age. No protective effect was found for colon cancer. In another case-control study, conducted in Belgium by Tuyns et al. (1987a), there was no indication of a protective effect of vitamin C.

The effect of vitamin C has also been assessed in several studies of other cancer sites. In a case-control study of laryngeal cancer, Graham et al. (1981) found an inverse relationship between risk and indices of both vitamin C and vitamin A consumption after controlling for cigarette smoking and alcohol consumption. There was a similar relationship for vegetable consumption in general. Wassertheil-Smoller et al. (1981) reported an association between vitamin C consumption and uterine cervical dysplasia in a case-control study in New York. The findings persisted after the investigators controlled for sexual activity. Stahelin et al. (1984) evaluated plasma vitamin C in a cohort of more than 4,000 men primarily studied for the risk of cardiovascular disease. Plasma vitamin C was found to be consistently lower in cancer cases than in controls. The largest differences were for cancers of the lung and stomach. Boing et al. (1985) analyzed regional nutritional data from a national survey on income and food consumption in the Federal Republic of Germany and correlated mortality rates with the food consumption data for 15 nutrients. Significant positive correlations were found between vitamin C and cancers of the breast, prostate, liver, and colon. In a case-control study of lung cancer in Hawaii, however, Hinds et al. (1984) found no association between dietary vitamin C intake and lung cancer risk.