PRACTICAL EXERCISES 



The pinchcock having been closed, the bottle B is now tilted so that 

 the urine in "ttie thimble is gradually mixed with the hypobromite 

 solution, and the nitrogen given off is added to the air in the burette 

 and its connections. The level of the water in the burette is therefore 

 depressed. When gas ceases to be given off, and a short time has been 

 allowed for the whole to cool, the tube is raised till the level of the 

 water is once more the same inside and out. The level is again read 

 off; the difference of the two readings gives the volume of nitrogen at 

 the temperature of the air and the barometric pressure. In order that 

 the temperature of the water may be the same as that of the air, the 

 cylinder should be rilled a considerable time before the observations 

 are begun. 



For most clinical purposes sufficiently accurate results may be very 

 easily obtained with the so-called ureometer of Doremus (Fig. 195). 

 A little urine is poured into the side-tube A, the stopcock C being closed. 

 The stopcock is then opened for an instant, so as to fill its bore, and 

 then closed again. Any urine which has passed into the tube B is 

 washed out with water, and B is then filled with hypobromite solution. 

 A is now filled up with urine to the top of the 

 graduation. By opening the stopcock, i c.c. of 

 urine (or less if the urine is concentrated) is per- 

 mitted to pass into B and to mix with the hypo- 

 bromite solution. The nitrogen collects in B, and 

 when it has ceased to come off, the meniscus of 

 the liquid is read off. The corresponding degree 

 on the scale gives the amount of urea in grammes 

 contained in the quantity of urine employed. 



8. Estimation of the Ammonia in Urine (Folin's 

 Method) . Ammonia is liberated by addition of a 

 weak alkali (sodium carbonate). Then the am- 

 monia is driven out at ordinary temperature by a 

 strong current of air and taken up in decinormal 

 acid, which is then titrated with decinormal alkali. 



The apparatus employed consists of (i) A 

 cylinder of about 45 cm. height and 5 cm. diam- 

 eter, with a rubber stopper through which pass 

 two glass tubes. One of the tubes goes nearly to 



the bottom of the cylinder, and the other end is connected, through a 

 U-tube filled with cotton, with a tube containing sulphuric acid. The 

 second tube is cut off short below ths rubber cork, and its other end is 

 connected, through a U-tube containing cotton, with a sulphuric acid 

 tube (or with two in series). (2) A water-pump to draw or force air 

 through the apparatus (600 to 700 litres in an hour). 



Put into the first sulphuric acid tube 25 c.c., into the second 10 c.c. 

 decinormal acid and some water; into the cylinder 25 c.c. of filtered 

 urine, 8 to 10 grammes sodium chloride, 5 to 10 c.c. of petroleum or 

 toluol to prevent foaming, and last of all i gramme dried sodium 

 carbonate. At once close the cylinder and allow a strong stream of air 

 to pass through the apparatus. At a temperature of 20 to 25 (room 

 temperature), and using 600 to 700 litres of air an hour, all the ammonia 

 is in the sulphuric acid in one to one and a half hours. The contents 

 of the sulphuric acid tubes are put into a beaker and titrated with 

 decinormal alkali, using lac moid (litmoid) or rosolic acid as indicator. 

 Deduct the number of c.c. of alkali used from the number of c.c. of the 

 decinormal acid originally taken, and multiply the remainder by 1-7034 

 to get the quantity of ammonia in milligrammes. The method can be 

 employed also for albuminous urine. 



33 



Fig. 195. Doremus 

 Ureoraeter. 



