Saturated solution

“ 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. ”

“ When water is added to solid silver acetate, the salt will dissolve. If an excess of the acetate is used, equilibrium will result between the solid salt and its solution, when the solution is saturated at the temperature used. As the salt dissolves, it is more or less ionized, and in the saturated solution we have a [p140] condition of chemical equilibrium between the salt and its ions ”

“ Make a saturated solution of salt in water. First wash the plate with clear water; then immerse it in the saline solution, when it should be agitated, and the coating will soon disappear. Another process with a salt solution of half the strength of the above is very interesting and effectual. The plate having been dipped into cold water, is placed in a solution of common salt, of moderate strength; it lies without being acted upon at all; but if it be now touched on one corner with a piece of zinc, which has been scraped bright, the yellow coat of iodine moves off like a wave and disappears. ”

“ Since, as has already been stated, each solid substance has its own solubility curve, there are three separate curves to be considered in the case of sodium sulphate and water. Where two curves cut, the solution must be saturated with respect to two solid phases; at the point B, therefore, the point of intersection of the solubility curve of anhydrous sodium sulphate with that of the decahydrate, the solution must be saturated with respect to these two solid substances. But a system of two components existing in four phases, anhydrous salt—hydrated salt—solution—vapour, is invariant ”

“ 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. ”

“ Fig. 16.
of crystals of the solute, crystals will dissolve as solvent enters, and the solution remains saturated throughout. By an imaginary cycle of operations we may then justify the application to solutions of the latent heat have already assumed as applicable. \/T (v2â€"i>i) , P is the osmotic pressure, ture and X the heat of solution of when dissolving to form a volume equation which we In the equation dP/dT = T the absolute temperaunit mass of the solute of saturated solution in an osmotic cylinder. ”

“ Under certain conditions, however, a difficultly soluble substance may be produced in a solution, in a concentration far beyond its solubility, without the separation of a precipitate (evolution of a gas or formation of a separate liquid) and also without the formation of a supersaturated solution. Thus, when hydrogen sulphide is passed into an aqueous solution of arsenious oxide, the liquid acquires the yellow to orange color of arsenious sulphide and becomes opalescent. ”

“ The mass is evaporated to dryness and gradually heated to a red heat. After cooling it is moistened with water and washed into a beaker and the solid mass quickly separated. The clear liquid is poured off and the residue again washed with water. The 416clear liquid obtained is saturated with acetic acid, carefully evaporated to dryness and after solution in water, filtration and the addition of a little nitric acid, the chlorin therein is precipitated by a silver nitrate solution, and the precipitate collected and weighed as usual. ”

“ But, if no solid be present initially, or if the cooling be rapid, the liquid of composition x becomes supersaturated and may cool till the supersaturation curve is reached at b, and a cloud of A crystals comes down. The temperature may then rise and the concentration of B increase in the liquid in a manner represented by some such line as b f. The conditions may then remain those of equilibrium along the curve / E, but before reaching / the solution may become supersaturated with B and deposit B crystals spontaneously. The eutectic point may never be reached. ”

“ Let the solubility, which represents the concentration of the solvent in the membrane at this stage, be called c. The membrane may then be considered to be taking up in unit time just as many molecules from the solvent as it gives up to it (dynamic equilibrium) , exactly as, when water is in equilibrium with water vapor, we consider the water to be vaporizing just as fast as vapor is condensing to form water. Now, if a solution of sugar is placed on the other side of the membrane, the solvent will pass out of the membrane into the solution just as fast as it passes back into the pure solvent. ”

“ The solvent power which holds all these solid substances in solution, and which contributes to their agreeable taste, is the carbonic acid gas with which the water is so freely charged. This free carbonic acid gas is probably formed by the decomposition of the carbonates which compose the rock. The water, impregnated with it, becomes a powerful solvent, and, passing through different strata, absorbs the various mineral substances which compose its solid constituents. ”

“ When a precipitate is dissolved by the addition of a reagent, such as an acid, an alkali, ammonia, ammonium sulphide—chemical solvents most frequently used in analytical work—we may, as a general principle, consider that the reagent must affect one or both of the ions of the precipitate in question, suppressing it (or them) and thereby making solution possible. The problem of determining in what way the suppression of the ion is effected, must then be faced. ”

“ When two fluids are diffused together without undergoing any change of their chemical properties, they are said simply to be mixed, and not combined; as milk and water when poured together, or as oxygen and azote in the common atmosphere. So when salt or sugar is diffused in water, it is termed solution, and not combination; as no change of their chemical properties succeeds. ”

“ In organic chemistry, for instance, it is often found that when a substance is thrown out of solution, it is first deposited as a liquid, which passes later into the more stable crystalline form. In analysis, also, rapid precipitation from concentrated solution often causes the separation of a less stable and more soluble amorphous form. ”

“ Another relation at which he worked was that the diminution in the vapour-pressure of a solvent, caused by dissolving a substance in it, is proportional to the molecular weight of the substance dissolved—at least when the solution is dilute. ”

“ 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. ”

“ Since normal solutions of various reagents are all referred to a common standard, they have an advantage not possessed by empirical solutions, namely, that they are exactly equivalent to each other. Thus, a liter of a normal solution of an acid will exactly neutralize a liter of a normal alkali solution, and a liter of a normal oxidizing solution will exactly react with a liter of a normal reducing solution, and so on. ”

“ Water, from its extensive powers as a solvent, never occurs in a state of absolute purity, although the nature and degree of its contamination must necessarily vary according to circumstances and situation. It is generally found holding earthy matter in a state of mechanical suspension, or saline and other bodies in chemical solution. ”

“ 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. ”

“ If the dissociation of salts is a reality and is complete in a dilute solution, any of the properties of a saline solution whatever should be represented numerically as the sum of three values, of which one concerns the positive ion, a second the negative ion, and the third the solvent. ”

“ It is plain that the standard solutions must be scrupulously protected from concentration or dilution, after their value has been established. Accordingly, great care must be taken to thoroughly rinse out all burettes, flasks, etc., with the solutions which they are to contain, in order to remove all traces of water or other liquid which could act as a diluent. It is best to wash out a burette at least three times with small portions of a solution, allowing each to run out through the tip before assuming that the burette is in a condition to be filled and used. ”

“ If the mixture is deeply coloured, none will act characteristically. If carbonate of potass be present in such proportion as is often met with in the shops, the tests cannot be trusted to.
Process for Compound Mixtures.—The following method of analysis is applicable to all mixtures, organic and inorganic. Add water, if necessary, and filter; and if the fluid which passes through is tolerably free from colour, test a little of it with solution of starch and chlorine. ”

“ 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. ”

“ A grain of salt no larger than a pin-head dropped into a pint of distilled water, will give a distinct chlorine test when nitrate of silver solution is added. Stronger, or even weaker, salt solution can be used by the experimenter while he is working into practice. ”

“ The freshly prepared precipitate dissolves in nitric acid with a reddish colour; hydrochloric acid reduces it, with evolution of chlorine, and formation of cerous chloride, whilst sulphuric acid dissolves it with partial reduction, oxygen being evolved. If a solution of a ceric compound be dialysed for some days, a clear neutral solution is obtained, which contains the hydroxide in the colloidal condition; by evaporation of the solution, a gummy mass is obtained, which dissolves again in water to a clear solution. Electrolytes rapidly cause coagulation. ”

“ VII. In case the water be suspected to contain any salts, it will be advisable gently to boil a quantity of the dry substance obtained by distillation, in five or six times its weight of pure common distilled water, such as is totally divested of all mineral particles. By this process, the saline matter will be dissolved or suspended in such water, in the form of a solution, which, on being filtred, and evaporated to dryness, will re-produce its salt. ”

“ 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 ”

“ In moist air it fumes excessively, yielding hydrogen chloride by hydrolysis: TiCl4 + H2O = TiOCl2 + 2HCl, and is decomposed by water with separation of the hydrated oxide. If the compound be added slowly to a large quantity of cold water, and the clear solution warmed, the oxide formed by hydrolysis remains in colloidal solution. ”

“ Just as solids have the power of condensing gases upon their surfaces, to an extent proportional to that surface, and therefore to the state of fine division: so fine powders have the power of withdrawing from solutions solids held in solution, to an extent varying with the nature of the substance dissolved, and the absorbing solid. ”

“ The resultant tendency is for the solutions on the two sides of the membranes to become equal in concentration by movement of the liquid from the less dense to the more dense portion, instead of by movement of the dissolved materials toward the less dense part of the solution as in the case of diffusion when solutions of different concentrations are brought in contact with no membrane to interfere with free diffusion. ”

“ Each particle may react in some way on the solvent in its neighbourhood, but if the solution be so dilute that each of these spheres of influence is unaffected by the rest, no further addition of solvent will change the connexion between one particle of solute and its associated solvent. The only effect of adding solvent will be to separate further from each other the systems composed of solute particle as nucleus and solvent as atmosphere; it will not affect the action of each nucleus on its atmosphere. ”