Quantitative estimation.
For the convenience of analysis our saline matter may be divided into two portions, one of which is employed for determining the acids, the other for the bases. The first portion will enable us to ascertain the quantity of carbonic and phosphoric acids, of chlorine, and of sul phuric acid. From the second portion we obtain the potash, soda, lime, rnagnesia, iron, and alumina, if, as nunly occurs, the latter be present.
Other ingredients will usually be matter of special examination ; the details of the methods to be pursued are subjoined.
We begin by treating the salts to be exa mined with water (solution A). Nothing but carbonates and phosphates of the earths will thus remain undissolved (residue B).
(A.) Carbonic acid.—The aqueous solution is treated with lime-water, or with a mixture of ammonia and nitrate of lime, as long as any precipitate is produced. If no phosphates be present, this consists of carbonate of lime, the solution is boiled—filtered, the precipitate ignited, and after adding a few drops of strong solution of carbonate of ammonia heated below redness and weighed, 100 grs. of carbonate of Hine indicate 44 of carbonic acid When phos phates are present, we proceed as follows:— Phosphoric acid.—The precipitate obtained by lime-water, as thus directed, contains all the phosphoric acid that may be present. If there fore phosphates existed in our solution, the pre cipitate, after its weight has been carefully ascertained, must be dissolved in nitric acid, and caustic ammonia (free from carbonic acid) added in slight excess. The phosphoric acid separates as a gelatinous precipitate of phos phate of lime. It must be ignited and the weight deducted from that of the mixed pre cipitate previously obtained; the difference in dicates the quantity of carbonate of lime. The precipitated phosphate of liine contains 491 per 100 of phosphoric acid. Phosphate of lime dissolves in nitric, hydrochloric, or acetic acid without effervescence, and is thrown down by ammonia in a gelatinous form. The phos phates and carbonates being thus separated, the filtered solution is treated for, Ifydrochloric acid.— The quantity of this acid or of the chlorine it contains may easily be determined by precipitating the solution pretty strongly acidulated with nitric acid by means of nitrate of silver. The chloride of silver thus obtained is completely soluble in ammonia, but resists the action of strong nitnc acid even when boiling. The precipitate must
be ignited ; it should undergo fusion into a horny mass at a heat a little below redness. It is now weighed; 100 parts indicate 25 of chlorine.
Sulphuric acid may be precipitated from the filtered liquid or from any fluid suspected to contain it by acidulating (if not already acid), not too strongly, with nitric acid, and preci pitating with nitrate of baryta. The preci pitate should be well washed with boiling water as long as any thing is dissolved, then ignited and weighed. Boiling nitric acid is without effect upon it; 100 grs. contain 34.19 of sulphuric acid.
(B.) The insoluble portion consists of carbo nates and phosphates of the earths, and per haps of iron. We bring them into solution by means of nitric acid, and supersaturate with caustic ammonia to separate the phos phates; filter if necessary, and add oxalate of ammonia ; collect and ignite the precipitate, moisten with solution of carbonate of am monia; it is once more heated to incipient redness, and it then consists of carbonate of lime : the carbonic acid is estimated in the manner already directed. The filtered liquid is boiled with solution of carbonate of am monia; the magnesia, if any, precipitates and must be strongly ignited ; 100 parts indicate 110 of carbonic acid, which must be added to that combined with the lime.
Phosphoric acid.—The quantitative estima tion of this body is attended with some dif ficulty, as it cannot be effected by direct pre cipitation, but is inferred from the loss. The precipitate by caustic ammonia just obtained consists entirely of earthy phosphates and phos phate of iron. It is ignited and the weight ascertained. It is then brought into solution by means of concentrated hydrochloric acid, and ammonia'added until the precipitate from the still acid solution is no longer perfectly re dissolved. Acetic acid is now added and then more ammonia, taking care that the liquid is $till strongly acid. Phosphate of iron alone precipitates; this ii separated by filtration, and after strong ignition consists of 57.44 phos horic acid and 42.56 sesquioxide of iron. From the filtered liquid the lime and mag esia are separated by oxalate of ammonia and ' ^austic ammonia, as will presently be de icribed ; then deducting the united weight of .he oxide of iron, lime, and magnesia from that 3f. the ignited mixed phosphates, the remainder s phosphoric acid.