§ 113. rr.ixE. 219 



and determine carbonic acid in 1-2 grms. of eacli precipi- 

 tate in the usual manner; the first precipitate contains the 

 total carbonic acid, the second only the combined. 



d. Nitrogen, — The residue left in the boat in h may be 

 used for the determination of nitrogen, or another portion 

 of 5-10 c.c. of the urine may be acidified witli oxalic acid, 

 mixed with ignited gypsum, and evaporated to dryness. 

 In the former case this second residue will contain only so 

 much of the nitrogen as was not expelled in the form of 

 ammonia during the desiccation ; in the latter, the oxalic 

 acid will prevent the escape of any nitrogen as ammonia. 

 The dry substance may be completely rinsed off the sides 

 of the dish with some of the soda-lime used in the com- 

 bustion. 



Or, tliis method of Voit may be used. "Weigh out 

 nbout 5 c.c. of the urine, mix it in a shallow dish with 

 a sufficient quantity of fine quartz sand to absorb it all, 

 put the dish under the receiver of an air-pump, and ex- 

 haust the air ; the whole becomes quite dry in a few hours 

 and may be pulverized easily, and completely loosened 

 from the sides of the dish and mixed with the soda-lime. 



The combustion may be performed in a short combus- 

 tion-tube and very rapidly, without fear of losing any of 

 the ammonia. 



e. Actual ammonia. — Determine this by Schlossing's 

 method in 20 c.c. of the urine, after filtration to remove 

 slimy or sedimentary matters (§ 47, h). In the fresh urine 

 of horned cattle, the actual ammonia does not amount to 

 more than 0.009-0.01° |„, but in human urine it ranges as 

 high as 0.078 to 0. 143° t 



/. Complete analysis of the ash. — Evaporate 200-500 

 grms. of the urine to dryness, incinerate the residue, and 

 examine the ash as directed in Scheme IV., § 94. The ash 

 of the urine of herbivorous animals is poor in alkaline 

 earths, and 8-10 grms. will be required for their determi- 



