no PRACTICAL PHYSIOLOGY. [XVII. 



ADDITIONAL EXERCISE. 



12. Estimation of the Acidity. —This is done by ascertaining the amount 

 of caustic soda required to exactly neutralise lOO cc. of urine. As the soda 

 solution cannot be prepared by weighing the soda because of the varying 

 amount of water contained in it, the soda solution must be titrated with a 

 standard solution of oxalic acid. Make a nortnal solution of oxalic acid by 

 dissolving 63 grams of dry crystallised oxalic acid in 1000 cc. water, CoHoOj 

 + 2H0O = 126 [i.e. , half the quantity is taken because the acid is dibasic"). A 

 normal solution of caustic soda would contain 40 grams per litre (NaHO), i.e., 

 N'a = 23, H=i, O=i6) = 4o). i cc. =40 milligrams or .04 gram. Dissolve 

 150 grams of caustic soda in about 1000 cc, water. 



(a.) Preparation of Normal Caustic Soda. — Place 10 cc. of normal oxalic 

 acid solution in a beaker, add a few drops of alcoholic solution of rosolic 

 acid (orange solution), and allow the caustic soda solution to drop from a 

 burette until the rosolic acid gives a rosy-red tint. Suppose that to saturate 

 the acid 9.2 cc. of the soda solution are added, then to every 9.2 cc. 0.8 cc. 

 must be added to obtain a solution of which i cc. will correspond to i cc. of 



acid, so that for 1000 cc. of caustic soda 9.2 : 1000 : : 0.8 : a; ( '- = 86. 9 ) 



86.9 cc. water must be added. 



(6.) Determine the Acidity of Urine. — Place 100 cc. of urine in a beaker, 



and add to it from a burette the normal soda solution (i cc. =0.063 oxalic acid). 



It is better, however, to dilute the soda solution to obtain a deci-nonnal solu- 



N 

 tion — i.e., one tenth as strong). In this case, i cc. =.0063 oxalic acid. 



Place strips of red litmus-paper in the fluid, drop in the caustic soda, stir, and 

 add caustic soda until the litmus begins to turn blue. Suppose 15 cc. of 



the dilute ( - ) solution are used, then the acidity of 100 cc. urine = 



15x0.0063 = 0.0945; and suppose the total quantity of urine passed to be 

 1500 CO., then the total acidity of the urine passed m twenty- four hours ex- 

 pressed as oxalic acid= 1.417 grams. The result is merely approximative. 



LESSON xvn. 



THE INORGANIC CONSTITUENTS OP URINE. 



The constituents of the urine may be classified as follows : — 



(i.) Water and inorganic salts. 



(2.) Urea and relative nitrogenous bodies; uric acid, xanthin, 

 guanin, kreatinin, allantoin, oxaluric acid. 



(3.) Aromatic substances; ether-sulpho- acids of phenol, cresol, 

 pyrocatechin, hippuric acid, &c. 



(4.) Fatty nnn-nitrogenous bodies; oxalic, lactic, and glycerin- 

 phosphoric acid. 

 i5.) Pigments, 

 6.) Gases, 



