nate; its quantity should be more than sufficient to saturate the acid in the flask) is suspended with the flask A by means of a thread fixed in between the stopper and the neck of the flask. The apparatus is, in every other respect, arranged exactly like that described § 105.

The apparatus, when fully arranged and prepared, is equipoised upon the balance. The stopper is then slightly lifted, so as to release the thread by which the little glass tube with the bicarbonate is suspended; the operator must take care to refix the stopper air-tight as soon as the glass tube has dropped into the flask. A lively evolution of carbonic acid commences the very instant that the contents of the small glass tube come in contact with the fluid in A, and continues for some time at the same rate of briskness; it grows afterwards gradually slower, and finally ceases altogether, when the flask a is to be placed in a water-bath of from 122° to 131°. The evolution of carbonic acid recommences upon this immersion in hot water; when it has again completely ceased, the little wax stopper b is slightly loosened, the flask a removed from the water-bath, and suction applied to d (by means of a perforated cork) until the air ceases to taste of carbonic acid. The apparatus, when perfectly cool, is replaced upon the balance, and the original equilibrium restored by additional weights. The sum of the weights required to restore the original equilibrium is equal to the amount of the expelled carbonic acid. Every equivalent of nitric acid yields two equivalents of carbonic acid, (Na O, 2 CO2+NO,⇒Na O, NO +2 Ca O2).

2

The results are very accurate.* That this method will equally serve to determine most other acids, and that it is applicable to the determination of free nitric acid, consequently only in cases where the solution contains no other acid besides this, must be perfectly obvious to every one. The reason which induces me to assign this general method more particularly to nitric acid is, that we posses no other simple and accurate method of determining this acid.

* Vide New methods of Alkalimetry, &c., by Drs. C. R. Fresenius and H. Will, edited by J. Lloyd Bullock. Taylor and Walton, London.

II. SEPARATION OF NITRIC ACID FROM THE BASES.

a. Anhydrous salts.

a. The base is determined (by the appropriate method) and the proportion of nitric acid present inferred from the difference between the weight of the reduced base and that of the analysed nitrate.

B. The nitrate under examination is finely levigated and intimately mixed with from two to three parts of perfectly anhydrous borax; the mixture is introduced into a platinum crucible, and the latter weighed with its contents. A gentle heat is now applied, which is increased very gradually until the mass in the crucible is in a state of calm fusion, when it is allowed to cool, and finally weighed. The difference between the last and the first weight expresses directly the amount of nitric acid originally present in the analysed nitrate. The results This method is inapplicable to nitrate of ammonia. (SCHAFFGOTTSCH, Poggend. Annalen, vol. Ivii. p. 260.) b. Hydrated salts.

are accurate.

A sample of the nitrate under examination is divided into two portions, and the base determined in the one by the appropriate method, the water and acid, (the latter from the volume of nitrogen gas); in the other portion, according to the method of organic elementary analysis, (§ 148,) expelling the air from the combustion tube by means of carbonate of lead, heated to incipient decomposition, instead of using bicarbonate of soda for this purpose, as recommended at § 148. Should the operator not possess the mercury necessary for the latter method, he may confine himself to determine the base and the water, and infer the proportion of nitric acid from the difference between the joint weight of these two constituents and the original weight of the analysed nitrate.

c. Soluble salts, the bases of which are completely precipitated by barytes or sulphuret of barium.

The solution of the nitrate under examination is mixed with

water of barytes (or with sulphuret of barium) until it manifests an alkaline reaction, and the base in the precipitate determined by the appropriate method; the filtrate is evaporated to dryness, the residue extracted with water, and the solution of nitrate of barytes thus obtained, treated according to the directions given at I., a., (the solution of nitrate of barytes must not manifest an alkaline reaction). Should sulphuret of barium have been used as precipitant, the extraction of the residue is to be effected according to II. d., (the excess of the sulphuret of barium added, changing, upon evaporation in the air, into insoluble sulphate and hyposulphite of barytes.)

d. Nitrate of barytes, strontia, and lime.

The solution of the salt under examination is mixed with sulphuric acid in very slight excess, and, in the case of the nitrate of strontia and lime, alcohol added to render the precipitation more complete. The fluid is filtered off from the precipitate, and water of barytes dropped into the filtrate until the reaction is feebly alkaline; the mixture is then evaporated to dryness in the water-bath, and the residue heated with water, (which must not lose the slight alkaline reaction during the process); the resulting solution is subsequently filtered off, and the residue washed with boiling water upon the filter until the last rinsings remain perfectly clear and transparent when tested with sulphuric acid. The solution of nitrate of barytes thus obtained is finally treated according to I. a.

e. Soluble salts of the fifth and sixth group.

The highly dilute solution of the salts under examination is introduced into a bottle, provided with a glass stopper, and mixed with strongly saturated sulphuretted hydrogen water in very slight excess, (the exact point may be attained best by adding the sulphuretted hydrogen water in small portions, and agitating the flask after every fresh addition).

The precipitate formed is allowed to subside, the fluid filtered off from it, and the filtrate treated according to the directions of II. d. (The sulphuret of barium which forms upon the satu

ration of the filtrate with water of barytes, changes, upon evaporation in the air, into insoluble sulphate and hyposulphite of barytes.)

f. Insoluble nitrates of metallic oxides may also be decomposed by digestion with sulphuretted hydrogen water or with solution of sulphuret of barium; it is more advisable, however, to analyse them according to II. a. or b., which are, moreover, in every respect the most appropriate of all the methods which I have described, and preferable to c. d. and e., in all cases admitting of the choice, since the three latter methods are very circuitous, and demand the most careful performance of the several operations.

§ 113.

2. CHLORIC ACID.

I. DETERMINATION.

Chloric acid is either converted into hydrochloric acid, for the purpose of its quantitative estimation, or its proportion is determined from the loss of weight which the analysed chlorate suffers in the process of decomposition, or finally, its amount is calculated from the volume of oxygen which it yields.

Free chloric acid in aqueous solution is determined most simply in the following manner. The solution containing the chloric acid is mixed with an aqueous solution of sulphurous acid until the mixture smells strongly of the latter, even after repeated agitation of the flask which contains it; the flask is then stoppered, and its contents are digested for some time; dilute solution of bichromate of potass is then added until the odour of sulphurous acid has completely disappeared, when nitric acid is added, and subsequently solution of nitrate of silver in excess, the further process being conducted according to § 107. The proportion of chloric acid originally present in the solution is calculated from the amount of chloride of silver obtained.

II. SEPARATION OF CHLORIC ACID FROM THE bases. The salt under examination is introduced into a crucible and

exposed to a gentle heat, which is gradually increased to intense redness, (the crucible being covered,) and maintained thus until the weight ceases to vary. The residue contains either a metallic chloride (this is the case, for instance, with alkaline chlorates, and with chlorate of lead, chlorate of silver, &c.) or a metallic oxide, in the case of chlorate of alumina, for instance). The proportion of chloric acid originally present in the analysed compound is calculated from the loss of weight which the latter suffers in this process. If the salt under examination contains water, the ignition is to be effected in a small retort, and the escaping gases are to be transmitted through a chloride of calcium tube. The amount of oxygen evolved may be inferred from the difference in the weight of the apparatus before and after the process; but the oxygen may of course also be collected and measured over mercury.

SECTION V.

SEPARATION OF BODIES.

§ 114.

Having thus disposed of the methods which serve to determine the amount of the basis and acids, present in simple compounds, we come now to those methods which are applied to analyse compounds or mixtures containing several or many bases and acids, and to determine the proportional quantity of every individual base, or acid, or, in other words, which serve to effect the separation of bodies from one another.

There are two ways of determining the proportional amount

.