1 6 THE VEGETABLE PROTEINS 



of separating the dissolved protein was long ago used by many, e.g., 

 Maschke (267), Sachse (445), Drechsel (95), Ritthausen (414), though 

 it was not recognised that this precipitation depends on the combina- 

 tion of the protein with acid until the writer's recent studies (312, 31 5) of 

 such combinations showed that this is almost certainly the case. (See 

 Chapter IV., p. 22.) The older idea that this solution of the protein 

 was caused by the alkaline phosphates is no longer tenable in view of 

 what is now known of the relations of proteins to bases and acids, and 

 of the small amounts of phosphates which exist in the seed, since recent 

 investigations have shown that nearly all of the phosphorus of seeds is 

 in organic combination. 



Water extracts only a small proportion of albumin from most of 

 the seeds yet studied, in regard to the character and occurrence of 

 which the reader is referred to Chapter X., p. 73, where the subject is 

 discussed in further detail. 



B. Extraction with Solutions of Neutral Salts. 



Ten per cent, sodium chloride solution is the solvent usually 

 employed for these extractions. This may be used either after the 

 ground seed has been extracted with water, in which case only those 

 proteins soluble in neutral saline solutions are obtained in the extract 

 or it may be applied directly to the meal, in which case the extract 

 will also contain nearly or quite all of the proteins which are extracted 

 by water alone. The latter method is the one which is usually adopted, 

 for it simplifies the process of isolating the proteins and reduces the time 

 necessary for making the extractions, which is an important considera- 

 tion, as changes appear to take place in the seed extracts, due probably 

 to enzyme action, which may lead to more or less alteration of the 

 dissolved proteins. The amount of protein extracted by sodium 

 chloride solution rarely represents all the protein which remains after 

 extraction with water, but in most seeds it forms a large part of the 

 total protein. The amount of protein thus extracted from different 

 seeds differs greatly. The cereals yield but a small proportion of their 

 total protein to neutral salt solutions while many of the oil seeds yield 

 a very large proportion. 



The general plan followed in conducting an extraction with sodium 

 chloride solution is to treat the ground seed with a sufficient proportion 

 of the solvent so that it will subsequently yield an extract of which so 

 much can be filtered clear as to be equal to about three-fourths of the 

 volume of the solvent applied to the meal. The proportion necessary 

 to attain this end depends not only on the amount of the insoluble re- 



