34 THE VEGETABLE PROTEINS 



separates on further evaporation in the form of a transparent film. The 

 addition of alcohol to the concentrated alcoholic solution precipitates 

 these proteins when the concentration of the alcohol reaches a certain 

 degree, which depends on the nature of the dissolved protein, for none 

 of them is at all soluble in alcohol free from water. On the other 

 hand, these proteins are precipitated on adding water to their alcoholic 

 solution when the concentration in alcohol is reduced to a certain de- 

 gree, which depends on the nature of the protein in solution. The 

 limits of concentration in either direction have not yet been determined 

 with accuracy, but, in general, solutions containing less than 50 per cent, 

 of alcohol or over 90 per cent, of alcohol dissolve very little of these 

 proteins with the exception of zein of maize, which is readily soluble 

 in alcohol of 92 to 93 per cent. 



Other alcohols than ethyl alcohol dissolve gliadin and zein and 

 possibly also the other alcohol-soluble proteins, although experiments 

 with these have not yet been made. Zein is readily soluble in methyl 

 alcohol and in commercial propyl alcohol. Kjeldahl (190) has shown 

 that gliadin is soluble in phenol and Mathewson (269) that it is soluble 

 in dilute methyl and propyl alcohol, in paracresol, and in benzyl alcohol, 

 and that from its solution in phenol it is precipitated by adding ether, 

 acetone, pyridine, benzene or chloroform. Mathewson also found that 

 methyl, ethyl, propyl and amyl alcohols all produce precipitates in the 

 phenol solution, the amount required being less the greater the molecu- 

 lar weight of the alcohol, but precipitates are not produced by adding 

 several volumes of aniline, phenylhydrazine or nitrobenzene, although 

 gliadin is not soluble in these latter substances. When dissolved in 

 phenol the solution can be heated to 140 without producing any not- 

 able effect on the specific rotation of the dissolved gliadin. 



