Soda.—After the potash has been determined, the corresponding quantity of chloride of pot assium is deducted from the weight of the mixed chlorides, and the deficiency inferred to be chlo ride of sodium; 100 grs. of chloride of sodium correspond to 53.33 of the anhydrous alkali. The platino-chloride of sodium, which the alcoholic solution contains, crystallizes in bold, well defined, flattened prisms readily soluble in water.
.Ammonia, when present in organic fluids, ainnot be quantitatively determined with ac curacy. Its presence is easily recognized by the chamcteristic pungent fumes which are given off when the residue of evaporation is mixed with caustic potash and gently warmed.
(B.) /ron.—The precipitate by carbonate and caustic ammonia from A and the insoluble re sidue B are dissolved in hydrochloric acid. When no phosphates are present, the acid solution is nearly neutralized by caustic am monia ; then an excess of hydro-sulphuret of ammonia added; the iron falls as a black sul phuret. This is collected on a filter, washed, re.dissolved in' hot hydrochloric acid, and the iron thrown down as sesquioxide by ainmonia in excess. It is thus completely separated from lime and magnesia.* If the earthy phosphates are present in mix ture with iron, the process already described, when speaking of phosphoric acid, must be employed.
Lime.—The acetic solution of the phos phates filtered from the iron, or if no iron be present, the acid solution supersaturated with ammonia and the precipitate re-dissolved in acetic acid, (a precaution indispensable, as 'oxalate of lime is soluble in nitric or hydro chloric acids,) is treated with solution of ox alate of ammonia in excess. A white precipitate of oxalate of lime falls ; it is allowed to stand some hours in a warm place (the liquid would otherwise pass turbid through the filter), sepa rated by filtration, ignited, and then moistened with a saturated solution of carbonate of am monia, after which it is thoroughly dried at a temperature short of redness. Carbonate of lime is thus obtained ; 100 grs. contain 56 of pure lime.
_Magnesia. filtered liquid is super saturated with ammonia, well agitated, and al lowed to stand for some hours; if any mag nesia be present, it separates as a crystalline precipitate, which must be washed with a weak solution of phosphate of ammonia; it is dried and ignited; the residue contains 35.71 of magnesia in every 100 grs.
Our ordinary analysis terminates here.
Lead is sometirnes found as a morbid con stituent of certain parts, more particularly of the soft solids; the fluid or part to be examined is dried and incinerated, (if bulky, in a clean earthen crucible,) and the charcoal burned off' as far as may be; the residue is digested in nitric acid diluted with thrice its bulk of water, filtered, nearly neutralized by ammonia, and a current of sulphuretted hydrogen transmitted through the liquid. The gas is easily gene mted for this purpose by adapting to a com mon phial a glass tube bent twice at ri angles, one limb being considerably 1 than the other ; the short limb passes air through the cork of the phial, and the plunges nearly to the bottom of the liqu be examined. In the phial 100 or 20 of coarsely bruised proto-sulphuret of are placed, and an ounce or two of sulphuric acid (1 of acid and 5 or 6 of w abundant effervescence arises from the engagement of the sulphuretted hyd If lead be present in the tested liquid, a or black precipitate of sulphuret of lead and the liquid becomes milky from the decomposition of the gas; svhen it s strongly of the sulphuretted hydrogen, the liquid is filtered, the precipitate is treated with nitric acid, to which a few drops of sulphuric acid have been added, and the whole ignited ; a white residue of sulphate of lead is obtained, which contains 68.42 per cent. of metallic lead. Sulphate of lead is insoluble in acetic acid, but is completely dissolved by a strong solution of acetate of ammonia.
The presence of copper is determined in the same way by incineration, treatment with nitric acid and sulphuretted hydrogen ; the resulting sulphuret is dissolved in nitric acid, and the oxide thrown down from the boiling solution by excess of caustic potash : it is ig,nited and weighed ; 100 parts contain 80 of metallic copper. If the nitrate of copper be treated with ammonia instead of potash in excess a beautiful transparent blue solution is obtained, which, when procured as just mentioned, is characteristic of the presence of copper.
Mercury, arsenic, antimony, and a variety of other substances may occasionally be met with after poisoning with these bodies ; but abundant directions for their discovery are given in the works on Toxicology, and to these, and in particular to the excellent treatise of Dr. Christison, the reader is referred.