20 THE VEGETABLE PROTEINS 



times be thus dissolved by alkalies, apparently this is not generally the 

 case as the majority of seed proteins have more pronounced basic pro- 

 perties than acid, and the reason that these dissolve when treated 

 with alkalies is often due to the fact that combined acid is neutralised 

 and the protein set free in a soluble condition. (Compare Chapter 

 IV., p. 28.) 



When compounds of protein insoluble in neutral or acid solutions 

 exist in the seed the acid and the protein both pass into solution on 

 treatment with alkali, and when such solutions are neutralised or acidi- 

 fied, and if a relatively insoluble combination of the protein with the 

 organic acid is possible, the two recombine, and a salt of the protein 

 with the organic acid, rather than with the acid employed for neutra- 

 lising, results. Thus if the protein is combined with nucleic acid, solu- 

 tion may result from double decomposition of protein nucleate with 

 the formation of soluble alkaline salts of nucleic acid from which the 

 nucleate is regenerated on adding acid. It is almost certain that, in 

 very many cases, the so-called nucleins and nucleo-proteins which 

 have been described are products of this character, that is protein 

 nucleates. (See Chapter X., p. 82.) The alkaline solution used for ex- 

 tracting proteins may be either very dilute solutions of caustic alkalies, 

 usually O'l to 0*2 per cent, potassium hydroxide or dilute solutions of 

 alkaline carbonates or bicarbonates, 0*50 to ro per cent. The choice 

 of the proper solvents depends on circumstances which must be deter- 

 mined for each case, all unnecessary excess of alkali being avoided 

 since the concentration of the extract in hydroxyl ions should be kept 

 as low as possible. As most seeds yield slightly acid extracts or con- 

 tain weak bases combined with acids the extract made with dilute 

 alkalies has a less concentration in hydroxyl ions than the solution em- 

 ployed in making it. The amount of acid contained in the seed or 

 capable of development from it should, therefore, be carefully con- 

 sidered. The practice of employing acid and alkaline solutions for 

 dissolving proteins which contain definite concentrations of acid, and 

 having no regard to the amount of protein or its state of combination 

 with acids or bases, is to be avoided as far as possible in attempting to 

 obtain preparations of proteins with unchanged properties. 



D. Extraction with Alcohol. 



Extraction with somewhat diluted alcohol, that is alcohol of 70 to 

 80 per cent., has been employed to remove a part of the protein from the 

 seeds of cereals, but proteins which dissolve in this solvent have not been 

 found in any other seeds. Extracts with alcohol can be made at any 



