APPENDIX. 837 



diluted urine should exactly occupy the bulb and neck of the tube, no 

 bubble of air being below the elastic band on the one hand, while on 

 the other the fluid should not rise above the band; in the former case 

 a little more water should be added, in the latter a fresh portion of 

 urine must be used, and the experiment repeated. After adjusting the 

 glass rod, fill up the rest of the bulb tube with hypobromous solution; 

 it will not mix with the urine so long as the rod is in place. The 

 water-bath having been previously erected, and the india-rubber cork 

 fixed firmly into the aperture, the bulb tube is to be thrust from below 

 through the perforation in the cork. The greater part of the tube is 

 then beneath the water-bath, the upper extremity alone being grasped 

 by the cork. Fill the water-bath half full of water, fill also the grad- 

 uated glass tube (e) with water, and invert it in the bath; in doing 

 this no air must enter the tube, which when inverted should be com- 

 pletely filled with water. Now slide the graduated tube toward the 

 orifice of the bulb tube, at the same time withdrawing the glass rod 

 which projects into the bath through the cork. At the instant that the 

 rod is withdrawn the hypobromous solution mixes with the diluted 

 urine, and a decomposition takes place represented thus : CONaH^ + 

 SNaBrO + 2NaHO = 3 NaBr + 3H 2 + Na 2 C0 3 + N 2 . Urea -f sodium 

 hypobromite -j~ caustic soda = sodium bromide -j- water -j- sodium carbon- 

 ate -j- nitrogen. The nitrogen produced is given off as gas, and dis- 

 places the water in the graduated tube, which is held over it. The gas 

 is at first evolved briskly, but afterward more slowly; to facilitate its 

 evolution, the bulb of the tube may be slightly warmed with a spirit 

 lamp; as a rule, however, this is unnecessary. After ten minutes, the 

 amount of water displaced by the gas should be read off on the tube, 

 which is divided into tenths. Each number on the tube represents one 

 gram of urea in 100 c.c. of urine. Normal urine should yield roughly 

 1.5-2.5 parts of nitrogen by this test. If 5 c.c. of urine gives off more 

 nitrogen than fills the tube to iii., dilute the urine with an equal volume 

 of water, and take 5 c.c.; read off and multiply by two.* 



Several apparatus may be employed instead of the one described, viz., 

 those of Dupre, Gerard, and Squibb. The chemical reactions in each 

 case are the same. 



(ii.) Liebig's Method. This method is of greater accuracy. The 

 solutions required are (a) baryta mixture = 2 vols. of saturated solution 

 of barium nitrate and 1 vol. of saturated solution of barium hydrate; 

 (b) standard solution of mercuric nitrate, such that 1 c.c. will precipitate 

 .01 grm. of urea, and (c) a solution of carbonate of soda. 



Method. Take 40 c.c. of urine, add 20 c.c. of (a), filter off the pre- 

 cipitate of sulphates and phosphates; keep the filtrate. Fill a burette 



* Several corrections have to be made before the result can be considered as 

 accurate ; for these the detailed accounts in practical handbooks of Physiology 

 should be consulted. 



