100 



CHEMICAL PHYSIOLOGY. 



2. Quantity. 0-5 gramme (7-10 grs.) daily. The ratio of uric- 

 acid to urea is about 1 : 45. It is dibasic, colourless, and 

 crystallises, chiefly in rhombic plates, and when the obtuse angles 

 are rounded the " whetstone " form is obtained. It often 

 crystallises spontaneously in rosettes from saccharine diabetic 

 urine. It is tasteless, reddens litmus, and is very insoluble 

 in water (18,000 parts of cold and 1500 of warm water), 

 insoluble in alcohol and ether. In the urine it occurs chiefly 

 in the form of acid urate of soda (C 5 H 2 N 4 O a , HKa) and potash. 



(a.) In a conical glass, add 5 parts of HC1 to 20 parts of 

 urine, put it in a cool place, and allow it to stand for twenty- 

 four hours. Yel- 

 low or brownish 

 coloured crystals 

 of uric acid are 

 deposited on the 

 sides of the glass, 

 or form a pellicle 

 on the surface of 

 the fluid like fine 

 grains of cay- 

 enne pepper. 

 Both uric acid 

 and its salt s 

 (urates) when 

 they occur as 

 sediments in 

 urine are col- 

 oured, and the 

 colour is deeper 



Fig. 25. Uric acid. a, Rhombic tables (whet- 

 stone form) ; 6, barrel form; c, sheaves ; d, 

 rosettes of whetstone crystals. 



the more col- 

 oured the urine. 

 The slow separa- 

 tion of the uric 

 acid is probably due to the presence of phosphatic salts. 



(b). Collect some of the crystals and examine them 

 microscopically. The crystals assume many forms, but are 

 chiefly rhombic. They may be whetstone, lozenge-shaped, 

 in rosettes, quadrilateral prisms, &c. They are yellowish in 

 colour, although their tint may vary from yellow to red or 

 reddish-brown, depending on the depth of the colour of the 

 urine. (Figs. 25, 26.) 



