390 Journal of Agricultural Research voi. xiii, no. s 



in this field.^ Almost every conceivable factor has been investigated 

 with more or less thoroughness; yet — 



no one is believed to have discovered a limiting factor or group of factors which com- 

 pletely solves the problem (j). 



Instead we wish to limit the discussion to those papers bearing di- 

 rectly upon our problem, the colloidal properties of the gluten. 



It is only within comparatively recent years that the fact has been rec- 

 ognized that the physical state of matter is of paramount importance. 

 When the nature of colloids was first investigated it was supposed that 

 relatively few substances could form colloidal solutions or gels, but it 

 now seems probable that under suitable conditions any substance may 

 be obtained in colloidal form, and it appears almost equally probable 

 that at some future date we may be able to obtain in crystalloidal form 

 those substances which we now know only as colloids. When a sub- 

 stance passes from the crystalloidal to the colloidal state, the physical 

 properties are so altered as to bear almost no resemblance to the original 

 substance; and even when in the colloidal state, the properties are not 

 constant but vary widely, depending upon the size of the colloidal 

 particles, upon their electrical charges, and upon the presence or absence 

 of foreign materials in the dispersion medium. This being the case, it 

 does not necessarily follow that, when two colloidal preparations of the 

 same material from different sources show identical chemical composi- 

 tion, they should also show identical physical behavior, for it is alto- 

 gether possible that one preparation lies much nearer the boundary 

 between the crystalloidal and colloidal states of matter than does the 

 other. 



Wood (j6) and Wood and Hardy (i8) have shown that w^heat gluten 

 is an emulsoid colloid. All proteins which have been investigated be- 

 long to this class. One of the most characteristic reactions of the 

 emulsoids is that they have a great affinity for water, being sometimes 

 classified as '"hydrophylic" colloids. The degree of this affinity for water 

 may be altered by the addition of salts, acids, or alkalis to the dispersion 

 medium. 



Hofmeister (7) was among the first to study the conditions causing 

 colloidal swelling of proteins and other workers have extended his ob- 

 servations. Fischer {4) has summarized the data of these workers and 

 added extensive experiments of his own. It has been found that the 

 addition of an acid or an alkali causes a hydrophylic colloid to imbibe 

 more water, which, if the colloid is in the form of a gel, results in a swell- 

 ing of the material, and that this swelling can be more or less completely 

 inhibited by the addition of salts. 



Wood appears to have been the first to attribute the differences be- 

 tween strong and weak flours to the physical properties of their proteins 



1 One of the latest of these r^sumds is that of Blisb (j). In his paper the various researches are reviewed 

 and criticised, and new data are added. 



