CHEMICAL DYNAMICS OF ANIMAL NUTRITION 131 



alteration of the albumen. In this way the albumen solution or tissue 

 can be dried (at a temperature not exceeding 38) and kept without 

 alteration for a considerable time. The tissue dried in this way can be 

 coagulated, and the nitrogen of the coagulum directly estimated. The 

 difference between the number thus obtained and the number obtained 

 by estimating the total nitrogen in the albumen solution or tissue 

 represents the residual nitrogen. 



The method has been carried out (in the case of serum) in the 

 following way : A measured quantity of serum is poured into a flat- 

 bottomed, glazed, porcelain dish. An equal weight (roughly) of 

 anhydrous sulphate of soda is then added. The mixture is then 

 allowed to stand for some time. The anhydrous sulphate of soda is 

 converted into the crystalline hydrated form, and the water is thus 

 abstracted from the serum. The dried mass can be readily removed 

 from the flat-bottomed dish by a knife (this is the reason for using a 

 flat-bottomed dish instead of an evaporating basin) and powdered in 

 a mortar. When finely powdered it is transferred to the Kjehldahl 

 flask in which the incineration with sulphuric acid is carried out (a 

 700 c.c. round-bottomed Jena flask was always used for this purpose). 

 Any small amount of the powder remaining in the porcelain dish or 

 mortar can be removed by rubbing the vessels with small fresh 

 quantities of anhydrous sulphate of soda, which is then added to the 

 main quantity. The albumen is then coagulated by boiling the mixture 

 in the Kjehldahl flask with absolute alcohol (100 c.c. alcohol for 15 c.c. 

 serum, or 50 c.c. alcohol for 5 gr tissue) for half-an-hour with reflux 

 condenser. The alcohol is then decanted off on to a filter. Water is 

 then added to the powder remaining in the flask (300-400 c.c.) and 

 the mixture is then heated on a water bath. By this means the sulphate 

 of soda and non-coagulable bodies are dissolved up and the coagulum 

 remains suspended in the solution in the form of a fine powder. The 

 water is decanted off through the same filter as that used for the 

 alcohol, and the greater part of the coagulum remains behind in the 

 Kjehldahl flask. This is again heated with water on a water bath, and 

 the hot water is again decanted off through the filter. When the 

 washings are free from sulphate of soda and have run through the 



