ANALYSIS OF URINE 



503 







Micro methods other than those of Folin for determining total nitrogen 

 have also been devised. Pregl oxidises the material in a wide test tube upon 

 which a small bulb is blown. The solution is made alkaline, the ammonia 

 js distilled over with steam through a special trap and collected in N/yo acid 

 and titrated with N/yo alkali using methyl red as indicator. 



Bang also 1 distils over the ammonia and titrates with thiosulphate after 

 Adding iodate and iodide to the acid. 



The method described by Wolf J is very simple and convenient : 



i c.c. of the diluted urine (or blood, see p. 579) is put into a 70 c.c. Jena 

 glass flask and oxidised by heating it, with a micro-burner, for --1 hour with 

 i c.c. of fuming sulphuric acid containing 7 per cent, of SO 3 , i gm. of potas- 

 sium sulphate and a drop of 5 per cent, copper sulphate solution. 2 c.c. of 

 water are added and, when cold, 4 c.c. of 40 per cent, caustic soda are tun 

 under the acid. The flask is fitted with a head piece containing a perforated 

 silver disc fused into it ; this is at- 

 tached by a rubber joint to block tin 

 tubing of -f$ inch diameter which is bent 

 over and fitted with a condenser, as 

 shown in Fig. 79. A glass tube drawn 

 out at one end is fitted to the end 

 of the tin tubing by means of rubber. 

 This is immersed in 5 c.c. of N/I4O 

 sulphuric acid. 



After the connections have been 

 made the acid and alkali in the flask 

 are mixed and distilled. The distilla- 

 tion takes about 5 minutes. After 

 washing the condenser with a few c.c. 

 of water, the excess of acid is titrated 

 as follows : 2 c.c. of 2 per cent, sodium 

 iodate and 2 c.c. of 2 per cent, potas- 

 sium iodide are added ; a narrow de- 

 livery tube through which pure air 

 purified by passage through cylinders 

 containing dilute sulphuric acid and 25 

 per cent, caustic potash and fitted with 

 calcium chloride tubes is put into the 

 solution ; the contents of the flask are 

 titrated with N/28o sodium thiosulphate 

 delivered from a 10 c.c. burette with 

 fine point and graduated in -^ c.c., 5 

 drops of i per cent, soluble starch solu- 

 tion being added as soon as the colour 

 of the iodine becomes faint. 



A control using all the reagents is 

 made at the same time and the amount 



FIG. 79. (From J. Physiol., 49, 90, 

 Cambridge University Press.) 



of thiosulphate used in the experiment is subtracted from the total amount 

 used in the control. 



i c.c. = o'oooi gm. nitrogen. 



Wolf distils over and estimates the ammonia obtained by the hydrolysis of 

 urea by Folin's method with potassium acetate in the same way, using 10 drops 

 of 40 per cent, caustic soda to render the solution alkaline. 



ij. Physiol., 1914, 49, 8 9- 



