of Proteine Compound* in Vegetable Substances. 3^3 



importance to the determination of the amount of proteine 

 compounds in different kinds of vegetable food ; and such a 

 determination becomes of the utmost importance both to the 

 physiologist and from a practical point of view. 



Hitherto, however, this desideratum has been very imper- 

 fectly supplied, and the chemist has very inadequately an- 

 swered the question as to the proteine value of the different 

 vegetable foods. Gluten, legumen, vegetable caseine, vegetable 

 albumen, as the various proteine substances occurring in vege- 

 tables have been called, vary much in properties. Some of 

 them are soluble and others are insoluble in water : and some 

 are soluble in alcohol ; and it would be difficult to draw up 

 any general method of extracting the proteine compounds from 

 vegetables so as to be enabled to weigh the proteine compound 

 in a state of purity. Resort has therefore been had to ele- 

 mentary analysis ; and chemists have deduced the amount 

 of proteine compounds from the percentage of nitrogen found 

 on submitting the food to ultimate analysis. 



To this procedure there are several objections which have, 

 apparently, not been sufficiently insisted upon. Taking the 

 case of wheaten flour (which is much more favourable than 

 many other cases), the percentage of nitrogen is a little short 

 of 2'00 ; yet neither the Will-and-Varrentrapp process nor 

 the Dumas process of nitrogen-determination, as it is gene- 

 rally carried out, is at all adequate to the valuation of the pro- 

 teine substance in flour. 



The Will-and-Varrentrapp process, as those who have a 

 critical knowledge of it are aware, is subject to special failure 

 when it is applied to proteine substances, and is not a deter- 

 mination of nitrogen in these instances. 



The Dumas method, as usually practised, is uncertain when 

 it is applied to determine a minute quantity of nitrogenous 

 substance in presence of a large quantity of non-nitrogenous 

 organic matter. Possibly, if carried out with extraordinary 

 care and extraordinary precautions, the Dumas process might 

 become available for the purpose in view ; but those persons 

 who have practical knowledge of the difficulties besetting this 

 particular case will admit that extraordinary care would 

 indeed be required, and that the process would be too imprac- 

 ticable for general employment. 



The method by w T hich we seek to accomplish the task before 

 us is, we believe, especially adapted for this description of 

 work. 



We propose to measure the amount of proteine substances 

 in vegetables by the amount of ammonia which the vegetables 

 generate when they are subjected to the action of a boiling 

 solution of potash and permanganate of potash ; in fact, we' 



