392 Journal of Agricultural Research voi. xnr, no.s 



became increasingly rapid with increasing concentrations of acid, and no 

 practicable concentration could be found at which coherence reappeared.^ 

 Wood likewise observed that the addition of salts to the acid solution 

 counteracted in a large measure the effect of the acid. He therefore 

 postulated (17, p. 272) that — 



the variations in coherence, elasticity, and water content, observed in gluten extracted 

 from different flours, are due rather to varying concentrations of acid and soluble 

 salts in the natural surroundings of the gluten than to any intrinsic difference in the 

 composition of the glutens themselves. 



Wood and Hardy (17, 18) and Hardy (6) support this view in later 

 papers. 



Upson and Calvin {14) were the next to study the colloidal swelling 

 of gluten. They employed a more exact technic than did Wood,^ using 

 the method employed by Hofmeister (7) in his investigations on the 

 swelling of animal proteins. In their experiments the gluten was first 

 freed from starch by washing it in a stream of distilled water. It was 

 then pressed out between glass plates to a fairly uniform thickness and, 

 after standing for some time, was cut into small disks. These disks 

 were weighed to the nearest centigram, placed in beakers containing 

 acid solutions of varying concentrations, and allowed to remain for a 

 constant period of time. They were then removed, drained, and re- 

 weighed. The increase in weight due to imbibition of water was calcu- 

 lated to the amount imbibed per gram of moist gluten. The experi- 

 ments were then repeated, except that a series of salts was added to the 

 different concentrations of the acids. The addition of the salts caused 

 a diminution of the water imbibition. They found that in dilute acids 

 the gluten swells and — 



the disks puff up and take on an appearance somewhat resembling cotton balls, finally 

 becoming transparent, soft, and gelatinous. 



They furthermore found that the taking up and giving off of water 

 was largely reversible and, by neutralizing the acid after swelling of the 

 disks had taken place, it would lose water and again become a firm 

 coagulum. 



In a later publication (75) the same investigators give results of further 

 studies on the colloidal swelling of wheat gluten as related to baking 

 strength of flour and conclude that — 



strength is related to soluble acid and salt content of the floiur. Flotirs containing 

 acids and salts in such combinations as to favor water absorption will behave as " weak " 

 flours, whereas those containing acids and salts in such combinations as inhibit water 

 absorption will behave as strong flours when baked. 



1 Fischer {4) gives a different order for the effectiveness of adds causing swelling of animal proteins — 

 that is, (i) hydrochloric, (2) phosphoric, (3) lactic, (4) formic, (5) oxalic, (6) nitric, (7) acetic, (8) citric, 

 (9) sulphuric. The noteworthy differences between these two lists lies in the relative position of sul- 

 phuric acid. 



» Wood allowed the gluten to imbibe water until it lost coherence and began to disperse as a sol. Upson 

 and Calvin, on the other hand, determined the weight of the water imbibed by the gluten in a fixed period 

 of time and before imbibition had progressed far enough to cause dispersion. 



