Solubility

“ The conditions which regulate the solubility of bodies, and the power of solution, regarded either as a mechanical or a chemical process, are very obscure. We might be led to suppose, that those bodies possessing the largest amount of unoccupied space were capable of holding the greatest quantity of soluble matter dissolved. ”

“ If a salt exists as solid, the constituent ion concentration product equals the solubility product. The sum of the free charges from all available ions equals zero, insuring local charge neutrality. Given the salt , composed of anion and cation , condition 1 above implies that if exists as a solid then
where is the ion solubility product. ”

“ This result must hold good for any solution, but if the solution be dilute when saturated, that is, if the solubility be small, the equation shows that if there be no heat effect when solid dissolves to form a saturated solution, the solubility is independent of temperature, for, in accordance with the gas laws, the osmotic pressure of a dilute solution of constant concentration is proportional to the absolute temperature. ”

“ If the temperature at which this dense spontaneous shower of crystals is found be determined for different concentrations of solution, we can plot a " supersolubility curve," which is found generally to run roughly parallel to the " solubility curve " of steady equilibrium between liquid and already existing solid. When two substances are soluble in each other in all proportions, we get solubility curves like those of copper and silver shown in fig. ”

“ On the other hand, we possess exact methods of testing whether gases or solutes in dilute solution react one with another and of determining the equilibrium state which is attained. For if one solute react with another on adding the latter to its solution, then corresponding to the decrease of its concentration there must also be a decrease of vapour pressure, and of solubility in other solvents; further, in the case of a mixture of gases, the concentration of each single constituent follows from its solubility in some suitable solvent. ”

“ From this it is evident that the analogy of substances forming a solution plays an important part, and as aqueous and all other solutions are liquids, there is good reason to believe that in the process of solution solid and gaseous substances change in a physical sense, passing into a liquid state. These considerations elucidate many points of solution—as, for instance, the variation of the co-efficient of solubility with the temperature and the evolution or absorption of heat in the formation of solutions. ”

“ The solubility of itself and salts, when pure, in concentrated sulphuric acid, forming colourless fluids, “which do not acquire any coloration upon being heated to the point of incipient evaporation of the sulphuric acid, but which afterwards become yellow, and finally brown.” (Fresenius.) —5. Its solubility in concentrated sulphuric acid to which some nitric acid has been added, forming a colourless, or, at the most, only a faintly yellowish liquid.—6. It is wholly destroyed by heat.
A solution of quinine in acidulated water, and solutions of its salts, exhibit the following reactions:—1. ”

“ A solution is said to be saturated when it remains unchanged in concentration in contact with some of the solid. The weight of the solid which will completely saturate a definite volume of a liquid at a given temperature is called the solubility of the substance at that temperature. ”

“ A requisite of all chemicals to be employed is their ready solubility in water. Of substances intended for absorption [3] I have used but three, viz: iron, iodine, and extract of malt. The first of these I have employed [26] in anæmic and enfeebled conditions generally, but especially in chlorosis and chlorotic hysteria, with marked success. ”

“ For it must be allowed by all, that solubility, and other collateral circumstances, influence the course of chemical combinations, since they determine whether or not there shall take place that contact of elements without which affinity cannot possibly operate. ”

“ Chemical Composition. In all the varieties the predominant principles are tannin and extractive. Solubility. The best menstruum is diluted alcohol. Incompatible Substances, vide Gallæ. Mr. Thomson also states a fact which I have reason to consider quite correct, that the alkalies destroy the astringent properties of kino. All the varieties are soluble in solutions of pure potass and ammonia, and no precipitation takes place on the addition of water. Medicinal Uses. ”

“ Broadly speaking, water is the most general solvent, and alcohol is perhaps second in solvent power.
3. Temperature. The weight of a solid which a given liquid can dissolve varies with the temperature. Usually it increases rapidly as the temperature rises, so that the boiling liquid dissolves several times the weight which the cold liquid will dissolve. In some instances, as in the case of common salt dissolved in water, the temperature has little influence upon the solubility, and a few solids are more soluble in cold water than in hot. ”

“ It follows that if the thermodynamic heat of solution be positive, that is, if heat be absorbed to keep the system at constant temperature, the solubility will increase with rising temperature, while if heat be evolved on dissolution, the solubility falls when the system is heated. ”

“ When these active substances are administered as remedies, in small doses, the precept respecting their solubility is even more important, for in such cases the smallness of the quantity places their operation more immediately under the control of various incidental agents; destroy the solubility of a medicine, and you will probably divest it of those properties which render it useful. ”

“ The stability constants, and the concentrations of the components used, determine the limiting concentrations in which a given metal ion is capable of continued existence, and determine, therefore, the question whether an ionogen, of a given solubility, is capable of existence as a solid phase in a given system. ”

“ Chemical Composition. When pure it consists of oxygen, hydrogen, and carbon; the rectified æther however still contains some water and alcohol, for Lovitz obtained an æther of 632. Solubility. One part requires for its solution ten of water; with alcohol and ammonia it unites in every proportion. Solvent Powers. It is one of 268the most powerful solvents known in vegetable chemistry, as it dissolves balsams, resins, gum-resins, wax, camphor, extractive, &c.; it takes up about a twentieth of its weight of sulphur, but it exerts no solvent power upon the fixed alkalies. Forms of Exhibition. ”

“ Qualities. Crystals, long hexangular prisms; Taste, sour and slightly bitter. Chemical Composition. It is a bi-sulphate, consisting of two proportionals of acid, and one proportional of base. Solubility. It is soluble in twice its weight of water, as well as in alcohol. Med. Uses. It affords a convenient mode of exhibiting sulphuric acid combined with a saline purgative, in a solid form; as it is more soluble, so is it more active than the sulphate. Dose, grs. x to ʒij. It forms a grateful adjunct to rhubarb. ”

“ In truth, the problem is by no means so simple; for the conditions governing the solvency of uric acid in the blood are bewilderingly complex, subject as they are to the manifold variations in solubility exhibited by crystalloids in the presence of the many divers colloids. ”

“ The mixing of acid or basic dyestuffs even in dry powdered form is attended with the same disadvantages as in the state of solubility, for just as soon as they are dissolved in water the reactions commence and the natural process of precipitation takes place with all its attending disagreeable consequences. ”

“ Inorganic Constituents.—The inorganic constituents of course are entirely absorbed by the roots; and it is as a solvent for them that the large quantity of water continually passing through the plants is so important. They exist in the soil in particular states of combination, in which they are scarcely soluble in water. But their solubility is increased by the presence of carbonic acid contained in the water, and which causes it to dissolve, to some extent, substances otherwise insoluble. ”

“ Solubility. f℥j of water dissolves only grs. 24: the salt is insoluble in alcohol. Incompatible Substances. It is partially decomposed by the nitric and muriatic acids, in which case, a portion of the base being saturated, a corresponding portion of bi-sulphate results; this fact illustrates a chemical law of some importance, viz. that a substance less weakly attracted by another than a third, will sometimes precipitate this third from its combination with the second, in cases wherein a super, or sub-salt is readily formed. ”

“ The peculiar manner in which hydrogen gas appears to dissolve solid substances,—as iron, potassium, sodium, sulphur, phosphorus, selenium, and arsenic, may be explained by regarding the results as a manifestation of the powers of chemical affinity over the forms of bodies. In like manner, the solution of salt in water, or the mixture of alcohol in that fluid, may be viewed as chemical phenomena, although usually considered as simple cases of solution or mixture: alterations of temperature and other physical changes taking place in either. ”

“ The Decomposition of any remaining Portion, and the adoption of measures best calculated to obviate its absorption. Where the substance is in a solid form, and acts by absorption, we should be very cautious how we favour its solution; while, if it exists in a liquid state, our object must be to render its active portion insoluble; this problem involves a series of questions which are wholly chemical. In order to prevent, or retard, the absorption of the active matter, we must, to a great degree, depend upon the agency of vital adjuvants ”

“ This explains why salts are usually inactive and neutral in character, while acids and bases are active agents. Thus we see why the most positive or the most negative elements in general have the strongest affinities, while those intermediate in the list are inactive, and have weak affinities; why alloys of the metals are weak compounds; why a neutral substance, like water, has such a weak affinity for the salts which it holds in solution; and why an aqueous solution is regarded as a mechanical mixture rather than a chemical compound. ”

“ Application to Solutions.—In a system containing a solution we have to deal with two components at least. The simplest case is that of water and a salt, such as sodium chloride, which crystallizes without water. To obtain a non-variant system, we must assemble four phases—two more than the number of components. The four phases are (1) crystals of salt, (2) crystals of ice, (3) a saturated solution of the salt in water, and (4) the vapour, which is that practically of water alone, since the salt is non-volatile at the temperature in question. ”

“ C. Every liquid which, when placed in a white porcelain vessel to the depth of one inch, exhibits under daylight distinct color.
D. Every liquid which contains in solution, in every 100,000 [8] parts by weight, more than two parts of any metal, except calcium, magnesium, potassium and sodium.
E. Every liquid which in every 100,000 parts by weight contains in solution, suspension, chemical combination or otherwise, more than 0.5 metallic arsenic.
F. Every liquid which, after the addition of sulphuric acid, contains in every 100,000 parts by weight more than one part of free chlorine. ”

“ When a difficultly soluble substance is formed in a solution beyond the point of saturation of the solution, the substance in question separates from the solution in a new phase, according to the principles just laid down. Ordinarily, if the substance is a solid, a precipitate is formed; if a gas, a gas escapes; if a liquid, a liquid separates out, which is immiscible with the solution in which it is formed. ”

“ As experimental discovery advanced, the substances classed with acids have been constantly multiplying, and by a natural consequence the attributes connoted by the word have receded and become fewer. At first it connoted the attributes, of combining with an alkali to form a neutral substance (called a salt) ; being compounded of a base and oxygen; causticity to the taste and touch; fluidity, etc. The true analysis of muriatic acid, into chlorine and hydrogen, caused the second property, composition from a base and oxygen, to be excluded from the connotation. ”

“ If a fluid so simple as water, braided of only three molecules of Matter, two of hydrogen and one of oxygen, can be so powerful a solvent, it follows that a fluid so complex as the Ether, woven and interwoven of molecules of all the elements, that is, of molecules of every form of Matter, must be dynamic in the highest degree, must be an omnipotent solvent: if water, consisting of only two elements, can hold in solution, besides its own constituents, ten or a dozen other elements, the Ether, consisting of all the elements, a fortiori can hold in solution all these elements. ”

“ But when you shake or stir salt or sugar in water, the particles divide up into smaller and smaller pieces, until probably each piece is just a single molecule of the salt or sugar. And these molecules get into the spaces between the water molecules and bounce around among them. They therefore act like the water and let the light through. This is a solution. The salt or sugar is dissolved in the water. Any liquid mixture which remains clear is a solution, no matter what the color. Most red ink, most blueing, clear coffee, tea, and ocean water are solutions. ”