54 



Strength in Wheaten Flour. 



carbonic acid dissolved from the air. This can be proved in 

 many ways, most directly perhaps by the fact that careful 

 neutralisation of the carbonic acid will restore cohesion, A brief 

 but more detailed consideration of the action of acids, alkalis, 

 and salts is needed to make these points clear. 



Action of Acids and Alkalis. — Acids and alkalis produce the 

 same physical effects, but the latter also induce hydrolytic decom- 

 position of the gluten. The effect of acids is therefore more 

 easily followed, and for simplicity I propose to confine my 

 remarks to them. 



Gluten prepared in the ordinary way and immersed in distilled 

 water retains its cohesion unless measures be taken to wash out 

 the salt which it contains. In N/iooo of any strong acid cohesion 

 breaks down, and the change is more rapid as the concentration 

 of acid is increased up to about N/30. Further increase in con- 

 centration slows the rate of disintegration, until at N/12 for 

 hydrochloric acid, N/25 f° r sulphuric acid, and 1*75 N for phos- 

 phoric acid the gluten again becomes permanently coherent and 

 more tenacious and less ductile than in its original state. Weak 

 acids, such as oxalic, acetic, lactic, citric, and tartaric acids, 

 produce disintegration in dilute solution, but fail to maintain 

 cohesion even at very high concentration. 



30 



\LT 



I 20 





, COHESION 













COHESION 





NO COHL 



SION 





10 20 30 40 

 ► H z SO4 



Fig. 1. 



When salt is added to gluten which has lost cohesion owing 

 to the action of acid this property is restored, but the concentra- 

 tion of salt needed to undo or prevent the action of the acid 

 varies with the concentration of the acid in a remarkable and 

 characteristic manner. The relations can be best explained by 

 reference to the curve. The ordinates are concentration of 

 sodium chloride, the abscissae concentration of sulphuric acid, in 

 both cases expressed in grain equivalents per 1,000 litres. The 



