786 DISCUSSION ON WHEAT : 
sodium chloride, the abscissee concentration of sulphuric acid, in both cases 
expressed in gram equivalents per 1,000 litres. The curve gives the con- 
centration of salt and acid needed just to preserve cohesion. It will be seen 
that as the concentration of acid is increasing, the concentration of salt 
needed to maintain cohesion rises to a maximum and thence falls until a 
point is reached where the acid alone is sufficient. The curve encloses an 
area of no cohesion, while outside it is a region in which acid and salt 
maintain cohesion. 
Neither of these areas represents uniform states; as is characteristic of 
colloidal matter, they are areas of continuous changes. The curve which 
limits them is merely an arbitrary line which marks the place at which 
cohesion is so far reduced that it no longer suffices to maintain shape against 
the extraneous force of gravity. Any line, starting within the area of no 
cohesion and passing through it to the area of cohesion, traverses a system 
which is continuously changing—namely, a colloidal solution containing 
exceedingly fine particles of gluten which become continuously coarser until 
finally, at or near the intersection of the curve, they run together into 
COHESION 
30 
COHESION 
10 
NO sae 
10 20 30 49 
—— Hz S04 
rq. 1. 
a coherent mass of gluten. Beyond the curve the line, if it be inclined 
upwards, follows a system in which still further separation of water and 
gluten is taking place, the two becoming less and less miscible—the water- 
holding power of the protein less and less, its tenacity growing, its ductility 
diminishing. 
Electrolytes therefore do more than confer on gluten its mechanical 
properties; they determine also its power of holding water. They also 
determine the water-holding power of any other colloid matter present in 
the dough. 
Acids and alkalis destroy cohesion and disperse the particles of gluten 
just as they produce and stabilise non-settling suspensions in many types of 
colloidal solution—namely, by the development of a difference of electric 
potential between the particles and the water. The curve which connects 
the potential difference with the concentration of acid has the same form as 
the curve given in fig. 1. 
The foregoing analysis of the factors which control the physical proper- 
ties of gluten in moist dough lead us to a brief analysis of the source of 
‘strength’ in flour. It must be borne in mind that loaf-making includes 
two distinct operations, the making and incubation of the dough and the fixa- 
