PRACTICAL EXERCISES 521 



ing to 0-00282 gramme, instead of 0-00268 gramme urea. But it is 

 affectation to make this correction if, as is seldom done in hospitals, the 

 temperature is not taken into account. 



A convenient apparatus is shown in Fig. 195. In B place 10 c.c. 

 of a solution made by adding bromine to ten times its volume of 40 per 

 cent, sodium hydroxide solution. Mix 5 c.c. of urine with 5 c.c. of 

 water. Put 5 c.c. of the mixture into the thimble A, which is then set 

 in the small bottle B. The cork is now carefully fixed in B, and the 

 tube F being open, the level of the water in the burette is read off. 

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

 the urine in the thimble is gradually mixed with the hypobromite solu- 

 tion, 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 filled a considerable time before the observations 

 are begun. 



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

 is liberated by addition of a weak alkali (sodium carbonate). Then 

 the ammonia 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. 

 diameter, 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 the 

 rubber cork, and its other end is connected, through a U-tube con- 

 taining 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 lacmoid (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. 



9. Estimation of the Total Nitrogen. It is sometimes more important 

 to determine the total nitrogen of the urine than the urea alone. This 

 is conveniently done by Kjeldahl's method (or some modification of 

 it), which can also be applied to the estimation of the nitrogen in the 

 faeces, or in any of the solids or liquids of the body. It depends on the 

 oxidation of the nitrogenous matter (or, rather, in the case of urine, 

 mainly its hydrolysis) in such a way that the nitrogen is all represented 



