30 COLOURING MATTER. 



Creatinin is an alkaline body which exists in small quantity (about 0*1 per 

 cent. ) in urine. It is soluble in cold water, still more so in hot. From its 

 solution in boiling alcohol it crystallizes on cooling. On the addition of 

 syrupy solution of zinc chloride to its aqueous solution, characteristic warty 

 clumps are formed of the combination of zinc-chloride ((C 4 H 7 N 3 O) 2 Zn C1 2 ) 

 and creatinin, each of which is seen under the microscope to consist of 

 acicular crystals radiating from a centre (see Creatin, p. 32). 



Human urine contains a soluble yellow colouring matter 

 (urochrome) which is precipitated from its solution by 

 acetate of lead ; it also usually contains a colourless chro- 

 mogenous substance, which when treated with hydro- 

 chloric acid yields indigo-blue. Grape-sugar exists 

 normally in urine, but in very small quantity. As, how- 

 ever, both uric acid and creatinin reduce cupric oxide, the 

 presence of sugar cannot be proved by the copper test 

 unless these bodies have been previously removed. 



The yelloiv colouring matter of the urine is obtained by treating the liquid 

 with milk of lime, and allowing it to stand. After separation of the 

 deposit, the clear filtrate is precipitated by solution of plumbic acetate to 

 which ammonia has been added. The lead precipitate, having been treated 

 with just sufficient sulphuric acid to decompose it, yields a yellow solution, 

 which owes its colour to a body to which the name urochrome was given by 

 Thudichum. This body is soluble in water, insoluble in alcohol. Its solution 

 exhibits no absorption bands before the spectroscope. On boiling it for some 

 hours with sulphuric acid, various brown or black substances are formed, the 

 most characteristic of which (called uromelanine) is soluble in ammonia, and 

 is re-precipitated on neutralizing the solution with sulphuric acid. Of the 

 chemical relations of urochrome little is known. 



Indigo -forming substance. Urine (particularly that of the horse) when 

 mixed with half its volume of strong hydrochloric acid, becomes dark, and 

 after some hours exhibits a scum or sediment which contains indigo-blue 

 (C 8 H 5 NO). If this scum is collected on a filter and treated with ammonia, 

 a blackish substance with which it is mixed is dissolved and removed. If 

 after washing the filter with cold alcohol -(which dissolves out a red colour) 

 the filter and residue are boiled in the same solvent, a beautiful blue solution 

 is obtained, which, on cooling, deposits flocks of indigo-blue. 



The materials which constitute urinary deposits and 

 concretions may be divided into those of acid and of 

 alkaline urine, the former comprising uric acid, urates, and 

 calcic oxalate, the latter the calcic and magnesic phos- 

 phates, triple phosphate, and calcic carbonate. 



