33 2 ANALYSIS OF URINE. [CH. XIII. 



sulphuric acid (i in 10) to remove ammonia from the air. B is a large thick- 

 walled tube, 25 to 30 mm. by 200 mm. C is a sheet of rubber, about 2 mm. 

 thick, cut from a 2-holed rubber stopper. It fits loosely into B, and has a 

 small groove cut at the side. It decreases the risk of an alkali foam being 

 carried over into E, which is a tube similar to B. D can be 

 made from a broken 5 cc. pipette and may be loosely filled 

 with cotton wool. F is a tube sealed at the lower end with 

 holes bored in it, whilst still hot, with a hot needle. The tubes 

 B and E are conveniently held by means of a heavy wooden 

 block bored with two large holes. In place of the tube E, a 

 100 cc. flask with a wide neck may be substituted as shewn in 

 fig. 45. The advantage of the flask is that there is very little 

 risk of the standard acid being carried over with the brisk air 

 current necessary. The objection to it is that the depth of 

 the acid layer being decreased there may be a danger of loss 

 of ammonia. If the air current is a moderate one for the first 

 two minutes this risk is very slight, and perfect results are 

 obtained. 



An efficient suction pump or blast pump is also 

 required. 

 45- 



Method, (i.) Into B measure 5 cc. of the urine, and add 2 

 drops of caprylic alcohol to stop foaming. 4 or 5 drops of kerosene 

 can be used, but it is not an efficient substitute. 



(ii.) Into E measure 20 cc. of the standard sulphuric acid, 

 which should be between 0-04 and 0-07 N. If a flask is used it is 

 advisable to add about 20 cc. of distilled water to give a deeper 

 layer for absorption. 



(iii.) Place 4 to 5 grams, of pure dry potassium carbonate into B, 

 roughly measuring it with a suitable spoon. Immediately connect 

 up the apparatus, taking care that D is joined to F, and not to the 

 connexion for the pump. Turn on the water supply to the pump 

 so that a rather slow air current is drawn through. After 2 to 3 

 minutes, turn on the water to full pressure and leave it for 12 more 

 minutes. 



(iv.) Gradually stop the pump and disconnect the tube E. 

 Lift up the rubber stopper so that F does not dip into the acid, and 

 wash down the interior of F with distilled water, using a fine jet. 

 Repeat this twice, allowing time for proper drainage. Carefully 

 wash down the exterior of F with distilled water, add 3 or 4 drops 

 of methyl red and titrate with CO 2 - free soda, which may be between 

 0-03 and 0-06 N., according to the directions given on page 323. 



Calculation. Determine the percentage of nitrogen in the form of ammonia 



