232 THE URINE. 



on cooling is titrated to determine the excess of acid. Each cubic 

 centimeter of the decinormal ammonia present in the distillate cor- 

 responds to 0.003 gramme, viz., to 0.1 per cent of urea. 



From this result the amount of preformed ammonia and that 

 present in the 20 grammes of magnesium chloride must be deducted. 



If desired, the estimation can also be made with the urea-con- 

 taining filtrate obtained with Morner and Sjoquist's method, but 

 Folin states that the previous isolation of the urea in such manner 

 is probably not necessary. 



Estimation of the Preformed Ammonia (according to Folin). 

 Ten c.c. of urine are diluted to about 450 c.c., treated with 

 a small amount of burnt magnesia (0.5 gramme) and boiled for 

 forty-five minutes, the distillate being received in decinormal sul- 

 phuric acid. The ammonia is then determined by titration as 

 above. As a small amount of urea, however, is decomposed during 

 the prolonged ebullition, it is necessary to ascertain separately the 

 quantity of ammonia which is referable to this source. To this end, 

 the retort is opened at the expiration of forty-five minutes, and an 

 amount of water added which is approximately equivalent to that 

 of the distillate. The distillation is then continued for another 

 period of forty -five minutes, the distillate received in decinormal 

 sulphuric acid, and the ammonia referable to decomposition of the 

 urea estimated as before. The difference between the two results 

 indicates the amount of preformed ammonia that was originally 

 present. 



Estimation of the Total Urinary Nitrogen. KJELDAHL'S METHOD. 

 The method is based upon the observation that on treating urine 

 with a mixture of two parts of concentrated sulphuric aeid and one 

 part of fuming sulphuric acid and boiling, the entire amount of 

 nitrogen can be transformed into ammonium sulphate. This is 

 then decomposed with an excess of sodium hydrate and the liberated 

 ammonia estimated by distilling into a know r n amount of dilute acid, 

 and retitrating the excess of acid. 



Five c.c. of urine are treated in a Kjeldahl digesting flask with 

 a pinch of yellow oxide of mercury (about 0.3 gramme) and 20 c.c. 

 of the sulphuric acid solution. The mixture is boiled until a per- 

 fectly colorless solution is obtained. Vigorous ebullition, how- 

 ever, must be avoided, and the flask should be placed at an angle 

 of about 45 degrees, so as to prevent loss from spurting. The milder 

 the ebullition the better. On cooling, the contents of the flask are 

 transferred to a Kjeldahl retort, with the aid of a little distilled water. 

 Sodium hydrate solution (27 per cent.) is then added until the greater 

 portion of the acid is neutralized. The fluid is allowed to cool again, 

 and a few pieces of granulated zinc or a little talcum is thrown in, 

 when a mixture of the hydrate solution and of a 4 per cent, solution 

 of potassium sulphide is further added in excess. Of either solution, 

 40 c.c. are added in all. The addition of the latter is necessary, as 

 the mixture not only contains ammonium sulphate, but also amido- 



