SUMMARY. IO9 



which the flour is made. The character of the gluten and the commercial 

 value of the flour depend to a large extent on the proportion of gliadin to 

 glutenin. 



In the moist gluten these proteins are present combined with about twice 

 their weight of water, which is gradually lost on exposure to dry air or at an 

 elevated temperature. 



The gliadin and glutenin are present as such in the seed and are not, as 

 was formerly supposed, derived from other protein substances through the 

 action of an enzyme. This is shown by the fact that they may be obtained 

 directly from the flour by the same treatment as that which yields them from 

 the gluten and under conditions which preclude the action of an enzyme. 



GLIADIN. 



Gliadin is the most important of the five proteins above mentioned, not 

 only on account of its influence on the character of the gluten, and therefore 

 on the quality of the flour for domestic purposes, but also on account of its 

 unusual physical properties and chemical constitution. 



Gliadin, unlike most other protein substances, is freely soluble in relatively 

 strong ethyl alcohol. Although gliadin is wholly insoluble in absolute alcohol 

 and but slightly soluble in water, it dissolves in dilute alcohol, the solubility 

 increasing with increasing concentration of alcohol until a certain strength 

 is reached, when the solubility diminishes until, by absolute alcohol, it is no 

 longer dissolved. Exactly what strength of alcohol dissolves the largest 

 proportion of gliadin has never been determined, but the maximum solubility 

 is attained with about 70 per cent of alcohol by volume. 



Gliadin is also soluble in other alcohols, as methyl, propyl, and benzyl 

 alcohols, in phenol and paracresol, and also in glacial acetic acid. 



Gliadin is somewhat soluble in pure water, but less so in water containing 

 salts, though not wholly insoluble in solutions containing 10 per cent of 

 sodium chloride. Very dilute acid or alkaline solutions dissolve gliadin to 

 solutions which, by neutralizing, yield the gliadin apparently unchanged. By 

 stronger solutions of acids or alkalis the gliadin is altered, as is the case 

 with all other native proteins. 



All the usual color tests given by other protein substances are obtained 

 with gliadin, which therefore contains the groups that give rise to these re- 

 actions. Gliadin is much less easily converted into insoluble products than 

 are most other proteins. Its solution in 70 per cent alcohol can be boiled 

 for an indefinite time, and even concentrated until much of the alcohol has 

 been removed, without forming insoluble products. On heating with very 

 weak alcohol or with water this protein is gradually altered and becomes 

 insoluble in stronger alcohol, but the coagulated gliadin thus formed is in 



