The Colloidal Swelling of Wheat Gluten. 
15 
to total nitrogen, chemical composition of the individual proteins, 
ratio of wet to dry gluten, total amount of gas evolved during 
fermentation, and many others. In spite of the enormous amount 
of work on this subject carried out by many investigators, no one 
has yet succeeded in showing that any single physical or chemical 
factor bears a definite and constant relation to baking strength. 
Moreover, there is, at present, no unanimity of opinion among 
investigators as to the importance which should be attached to 
the different factors in their relation to baking strength. 
It now seems certain in the light of our experiments as well as 
those of Wood and Hardy that the colloidal properties of gluten 
are of far greater importance in this connection than is generally 
supposed; and that baking strength in wheat flour is to be 
associated with quality of gluten, which is, in turn, regulated by 
the kind and concentration of the soluble acids and salts present 
in the flour or added in the baking process. Quality of gluten, 
as washed from flour in the ordinary method, will depend first 
on the kind and concentration of the acids and salts present in 
the flour, and secondly upon the nature of the liquid with which 
the gluten is washed. If the kind and concentration of the acids 
and salts in the flour are such as to produce the ''acid effect," 
that is, to favor water absorption, then the gluten will be soft 
and gelatinous, — in other words will be a ''weak" gluten. If the 
kind and concentration of the acids and salts in the flour are 
such as to produce the "salt effect," that is, to prevent water 
absorption, then the gluten will be coherent and tenacious, — in 
other words, wifl be a "strong" gluten. Furthermore, as we 
shall show in the next section of this paper, the character of the 
gluten may be modified at will, depending on the character of 
the solution used for washing the starch from the flour. Dilute 
salt solutions and tap water give a gluten somewhat tougher 
and more elastic than does distilled water. Distilled water con- 
taining carbon dioxide gives a poorer quality of gluten than 
freshly boiled distilled water. Dilute acid solutions give a soft, 
gelatinous gluten. If acid solutions of such concentration as 
give maximum water absorption are used for washing the starch 
from flour, then it is practically impossible to obtain a gluten 
ball. The gluten is not destroyed but is simply rendered in- 
capable of being collected. 
The now generally accepted deflnition of baking strength in 
wheat flour is that suggested by Humphries and Biffin, namely, 
"the capacity for making large, shapely, and therefore well- 
aerated loaves." The power which dough made from wheat 
flour possesses, of retaining the bubbles of carbon dioxide formed 
during the fermentation, is due to the peculiar qualities of the 
