The watery solution of this extract is of a deep yellow colour.
It is not precipitable by the solution of bi chloride of mercury ; but the protochloride of tin, the di-acetate of lead, and nitrate of silver precipitate it of a dark brown colour.
The third extractive, which was precipitated neither by the acetate nor di-acetate of lead, possesses the following characters :— It is of a yellow colour. Solutions of bi chloride of mercury, protochloride of tin, and nitrate of silver precipitate its aqueous solu tion. The precipitate produced by the last of these re-agents is of a dirty yellowish red colour.
Colouring These are two in num ber, I-Immaphmin or the brown; and Uroery thrin, or the red.
a. is the substance which gives the yellow or broWnish yellow tint to urine, and according to its proportion the urine assumes a lighter or deeper colour. Ac cording to Scharling, the odour also of the urine depends on this principle. It is soluble in alcohol, and the alcoholic solution reddens litmus. The odour, when concentrated, is said to resemble that of castor. Scharling be lieves this colouring matter to be an oxide of a radical, to which he has given the name of omichmyle.
13. Uroerythrin. — This exists but in very minute quantity in healthy urine; it attaches itself especially to the lithic acid, being pre cipitated with that principle on all occasions. It becomes abundant in some forms of disease.
Mucus.—For the history of this substance see article Mucus.
Uric or lithic acid may be pro cured from the urine by the addition of a few drops of strong hydrochloric acid, which, after the lapse of some hours, produces a reddish crystalline precipitate of lithic acid. This red colour is caused by an admixture of colouring matter of urine, for pure lithic acid is per fectly white. It may be obtained in a pure state from the red crystals by being dissolved in caustic potash, and then precipitated from its solution by the addition of hydrochloric acid. The precipitate may now be collected, and washed on a filter.
Lithic acid possesses the following chemical properties :— It is insoluble in water.
It is easily soluble in a solution of caustic alkali, and precipitated from such solution by the addition of an acid.
It is dissolved by nitric acid with efferves cence; and, by careful evaporation to dry ness, yields a red or rather pink colour, which becomes of a fine violet tint when ammonia is dropped on it, or even when it is subjected to the action of strong ammoniacal fumes. This reaction of ammonia is very useful, in asmuch as it prevents the yellow stain which many animal matters produce with nitric acid from being mistaken for this reaction of lithic acid. In the former case, the ammonia in creases the yellow tinge to an orange colour, which is very distinct from the beautiful violet tint of what is now known as murexid.
Before the blowpipe, this substance emits a fetid sinell of burnt horn, mixed with an odour approaching to that of hydrocyanic acid.
The ultimate analysis of lithic acid shows its composition to be C 5, N 2, I-I 2, 0 3. Hippuric This acid is considered by Liebig to be constantly present in human urine.
He states its quantity as equal to that of the lithic acid, in all persons feeding on a mixed diet. This, however, is certainly an over statement. It is present, but in small proportion, in healthy urine.
The ultimate composition of hippuric acid is as follows :— C 18, H9, N1, 06.
It crystallises in four-sided prisms, obliquely truncated.
When heated it gives out an odour resem bling that of the tonquin bean.
Lactic lactic acid was first dis covered in the urine by Berzelius, who ex tracted it by the following process : A portion of urine was evaporated to dry ness, and alcohol of specific gravity 0.833 boiled on the solid residuum.
The alcoholic solution was next evaporated, and the mass dissolved in water.
The watery solution was then boiled with a considerable qUantity of hydrate of lime, till all ammoniacal fumes (from decomposing urea) were dissipated; the hydrate of lime now became coloured yellow, owing to the decomposition of animal matter.