ORGANIC ANALYSIS. 



before, separating it thus -into a solution (A), 

 and an insoluble residue (B). 



(A.) Potash. The solution rarely contains any 

 but the alkaline salts. If, however, any of the 

 earths are present, they must h'rst be separated 

 in the form of carbonates, by adding a mix- 

 ture of carbonate and caustic ammonia; the 

 filtered liquid is evaporated to dryness, the 

 residue ignited to expel ammoniacal com- 

 pounds and re-dissolved in water, which then 

 contains only salts of potash and soda. If 

 sulphuric or phosphoric acids be present, it is 

 necessary for a quantitative determination of 

 each alkali to convert the mixed sulphates or 

 phosphates into chlorides. The method for 

 accomplishing this object is rather circuitous : 

 chloride of barium in slight excess is added to 

 the solution, which is filtered from the sulphate 

 or phosphate of baryta that then precipitates ; 

 the filtered liquid is heated with a mixture of 

 caustic and carbonate of ammonia, again fil- 

 tered, evaporated to dryness, and ignited ; the 

 bases are thus obtained in their desired con- 

 dition of chlorides; they are then carefully 

 weighed, re-dissolved in a small quantity of 

 water; bichloride of platinum in solution is 

 added, and the whole evaporated to dryness on 

 a water-bath. The dry residue is digested with 

 rectified spirit, and the washing continued as 

 long as the liquid passes coloured through the 

 filter; the precipitate, consisting of anhydrous 

 double chloride of platinum and potassium, is 

 dried and weighed; 100 grs. indicate 19.43 of 

 potash. 



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-chlonde of sodium, which the 

 alcoholic solution contains, crystallizes in bold, 

 well defined, flattened prisms readily soluble 

 in water. 



Ammonia, when present in organic fluids, 

 cannot be quantitatively determined with ac- 

 curacy. Its presence is easily recognized by 

 the characteristic pungent fumes which are 

 given off when the residue of evaporation is 

 mixed with caustic potash and gently warmed. 



(B.) Iron. 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-sulphnret 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 ammonia 

 in excess. It is thus completely separated from 

 lime and magnesia.* 



* In the rare instances in which alumina presents 

 itself in the animal fluids, this earth would pre- 

 cipitate along with the sulphuret of iron, and would 

 again be thrown down with the sesquioxide. It is 

 however easily separated by digesting the oxide 

 while still moist in a solution of caustic potash ; 

 the oxide of iron alone remains behind. To sepa- 

 rate alumina from the alkaline liquid, it is feebly 



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. Awhile 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. 



Magntsia. The 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 sometimes 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- 

 rated for this purpose by adapting to a com- 

 mon phial a glass tube bent twice at right 

 angles, one limb being considerably longer 

 than the other; the short limb passes air-tight 

 through the cork of the phial, and the other 

 plunges nearly to the bottom of the liquid to 

 be examined. In the phial 100 or 200 grs. 

 of coaisely bruised proto-sulphuret of iron 

 are placed, and an ounce or two of dilute 

 sulphuric acid (1 of acid and 5 or 6 of water); 

 abundant effervescence arises from the dis- 

 engagement of the sulphuretted hydrogen. 

 If lead be present in the tested liquid, a brown 

 or black precipitate of sulphuret of lead falls, 

 and the liquid becomes milky from the partial 

 decomposition of the gas ; when it smells 

 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. 



supersaturated with hydrochloric acid, and again 

 rendered slightly alkaline by ammonia , the alumina 

 precipitates, is collected on a tiller, thoroughly 

 washed, ignited, and weighed. 



