64 THE VEGETABLE PROTEINS 



fall far short of the total of the protein. A considerable part of this 

 deficit is doubtless made up of the known substances that are deter- 

 mined, for losses necessarily occur in the processes of isolating and 

 separating them \cf. Osborne and Heyl (360)]. This loss, however, 

 probably does not account for all of the unknown residue. If it is 

 assumed that the amino-acids that are found in a well-conducted analysis 

 of the decomposition products of a protein are united in the molecule 

 with the elimination of water, and that the dibasic acids are united to 

 an amide group which replaces one hydroxyl, and the sum of the 

 percentages of these radicals is subtracted from 100, the percentage 

 of the unknown residue can be obtained. If the nitrogen unaccounted 

 for in the same analysis is calculated as per cent, of this unknown 

 residue, it is found that in the case of gliadin this unknown part con- 

 tains 13-3, in excelsin 14*0, and in legumin 14*3 per cent, of nitrogen. 

 Among the known decomposition products of the proteins this per- 

 centage of nitrogen is equalled only by glycocoll, alanine, tryptophane 

 and serine, even if the calculation is made for the radicals of the mono- 

 amino-acids in polypeptide union, that is, after subtracting one molecule 

 of water from their molecular weights. In making this calculation no 

 account is taken of the fact that the amount of the amino-acids isolated 

 in a condition fit for weighing is distinctly less than the quantities 

 actually yielded by hydrolysis. As this loss falls mostly on substances 

 which contain less than 1 3 per cent, of nitrogen, the actual proportion 

 of nitrogen in the unknown residue of the protein must be even higher 

 than that indicated by the above calculation. As it is improbable 

 that this unknown residue is wholly made up of undetermined quan- 

 tities of the four amino-acids above mentioned, it is fair to presume 

 that the proteins contain a considerable amount of some still unknown 

 substance or substances relatively rich in nitrogen \cf. Emil Fischer 

 (591)]. 



E. Sulphur in Vegetable Proteins. 



The small but constant quantity of sulphur which proteins contain 

 has especial interest in connection with the numerous attempts that 

 have been made to ascertain their molecular weights and to establish 

 empirical formulas for them. The fact that sulphur exists in two 

 forms in the protein molecule was long ago indicated, and it has since 

 been assumed that the protein molecule contains at least two atoms 

 of sulphur. It has been recently demonstrated that many proteins 

 yield cystine on hydrolysis, and the probability has become great that 

 much, if not all, of the sulphur of some of the proteins is cystine sul- 



