ORGANIC ANALYSIS. 



805 



Tlie 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 ignited 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. 



B. ANALYSIS OF ANIMAL SOLIDS. 



Solid matters, as tumours, concretions, and 

 sediments, are best subjected to a preliminary 

 test by the action of heat ; the sediments are 

 separated by filtration from the liquids in 

 which they are deposited ; by ignition on plati- 

 num foil of a few small fragments we observe 

 either, 



1. It is wholly or almost wholly dissipated, 

 in which case it consists of, 



Cholesterin, which fuses and burns with 

 flame ; 



Uric acid, or } which are gradually dissi- 



Urate ammonia, S pated, producing transient 

 blackening of the foil around; 



Cystic oxide, which is consumed with a pe- 

 culiar odour; 



Albumen, fibrin, or hairs, which swell up 

 and burn with flame: 



2. Or it blackens, leaving a less bulky re- 

 sidue ; 



In which case it may be 

 Urate of soda, potash, ( they leave an alka- 

 Lirne, or magnesia, S line ash, which in 

 the two first fuses at a red heat, or it may arise 

 from a mixture of some of the preceding list 

 with some of those that follow. 



3. Or, lastly, it undergoes little or no change 

 in bulk, when it is composed of 



Phosphates of the earths; 



Carbonate of lime, or magnesia; 



Oxalate of lime, which generally decrepi- 

 tates. 



Having by these simple trials acquired some 

 knowledge of the nature of the substance we 

 have to deal with, we proceed to a more spe- 

 cial examination. 



a. Cholesterin is the principal constituent of 

 biliary calculi in the human subject, mixed 

 with variable proportions of colouring matter. 

 These calculi, when numerous, generally pre- 

 sent facettes more or less flattened and po- 

 lished ; when solitary, they often attain consi- 

 derable bulk, and are usually crystaMme and 

 semitransparent on the surface. Before the 

 blowpipe they fuse and burn with a bright 

 smoky flame, leaving but little ash. Boiling 

 alcohol dissolves the cholesterin, and on cool- 

 ing deposits the greater part in pearly glisten- 



ing scales. Caustic potash dissolves the co- 

 louring matter and leaves the cholesterin. This 

 last reaction distinguishes it from other fats, 

 and particularly from lithofellic acid, recently 

 discovered as an occasional constituent of be- 

 zoars and of gall-stones in the inferior animals; 

 the lithofellic acid fuses at a higher tempera- 

 ture than cholesterin, and separates from its 

 alkaline solution as an insoluble fat on neu- 

 tralizing by a stronger acid. 



b. Uric acid generally assumes the form of a 

 reddish-brown crystalline sand, or of lighter- 

 coloured rounded masses. Before the blow- 

 pipe it blackens and burns away, leaving only 

 a minute trace of ash, usually alkaline, owing 

 to the presence of a very small quantity of lime 

 or soda. The manner of applying nitric acid, 

 so as to produce the characteristic colour from 

 the decomposition of uric acid, has been al- 

 ready mentioned. When powdered it dissolves 

 completely in solution of potash by the aid of 

 heat, and if the solution be supersaturated 

 with hydrochloric acid, uric acid again preci- 

 pitates in minute wliite crystals. 



The urates are much more soluble in hot 

 water than uncombmed uric acid : they form 

 amorphous deposits usually of a light brown 

 colour. 



Urate of ammonia before the blowpipe pre- 

 sents phenomena resembling uric acid; when 

 rubbed with solution of caustic potash, ammo- 

 niacal fumes are emitted. In its other reac- 

 tions, except that it is more soluble in boiling 

 water, it closely resembles uric acid. 



Urate of soda is distinguished by the large 

 proportion of fusible alkaline ash left on igni- 

 tion after the application of a red heat; the 

 residue dissolves with effervescence in hydro- 

 chloric acid and gives no precipitate when this 

 solution is treated with an alcoholic solution of 

 chloride of platinum. If potash were present, 

 it would be indicated by the formation of crys- 

 tals on adding this test. 



Urate of lime occasionally accompanies uric 

 acid; the residue by incineration then yields the 

 usual reactions of lime, such as a precipitate 

 with oxalale of ammonia when added to a 

 solution of the ash in acetic acid. 



c. Cystic oxide is wholly dissipated by heat, 

 emitting a peculiar odour. It is soluble readily 

 both in acids and alkalies, and is deposited in 

 hexagonal plates by spontaneous evaporation 

 of its ammoniacal solution. The peculiar form 

 of its crystal is at once recognized by the em- 

 ployment of the microscope. 



d. Albumen and Jibrin are discovered by 

 their solubility in diluted alkalies and in acetic 

 acid. Neutralization causes a flocculent preci- 

 pitate soluble in excess of acetic acid or of the 

 alkalies; the acetic solution gives a precipitate 

 on adding ferrocyanide of potassium. Before 

 the blowpipe they swell up, leaving a bulky 

 coal which burns with difficulty to a small 

 white or yellowish ash ; they always contain 

 saline matter. Albumen and fibrin, in com- 

 mon with all the compounds of protein, are 

 further characterized by dissolving slowly in 

 the concentrated acids; with sulphuric acid a 



