70 



Gluten of wheat flour is therefore a variable colloid when met 

 with in the bakery. It is upon the proportion of glutenin to gliadin 

 and upon the amount and quaUty of salts present that the nature of 

 the gluten of wheat flour depends. Unless these proportions are 

 known (obtainable only by laborious effort in the laboratory), it is 

 not possible for the chemist to predetermine the quaUty of the 

 resulting bread. " Washing out " accomiDanied by baking trials 

 are the speedier tests for the quality of a flour. 



Glutenin is in'soluble in water, saline solutions and dilute alcohol, 

 soluble in dilute acids and alkaUs, and reprecipitated from such 

 solutions by neutralisation. 



GUadin is insoluble in absolute alcohol ; soluble m dilute alcohol, 

 (sUghtly in 90 per cent, and very soluble in 70-80 per cent, alcohol), from 

 which it is precipitated by adding a large quantity of Mater or strong 

 alcohol, especially in the presence of miich salts. It is soluble in 

 distilled water, forming an opalescent solution from which it is 

 precipitated by addition of sodium chloride. 



Globulin is soluble in sodium chloride solutions, precipitated 

 therefrom by dilution or saturation with magnesium sulphate or 

 ammonium suljihate, but not with sodium chloride. Partly pre- 

 cipitated by boiling, but not coagulated at temperatures below 100" C. 



Albumin is precipitated from its solution by saturating with 

 sodium chloride or magnesium sulphate. Coagulated at 52° C. 



Coagulum and proteose are both probably formed during the 

 extraction of the gluten with water. The former is precipitated by 

 saturating its solution with sodium chloride, or by adding 20 per cent, 

 of sodium chloride and acidulating with acetic acid. On concen- 

 trating this solution, the proteose is coagulated, lea^'ing behind a 

 proteid called coagulum, which has not been separated in a pure state. 



The behaviour of wheat gluten under the influence of salts is, 

 therefore, clearly the result of complex and mutual action among 

 the various colloid components and electrolytes. Very little more 

 can be said definitely. 



Ostwald and Liiers [Koll-Zeits. 25, 26-15, 82-90. 116-136, 

 17.7-196, 230-240 (1919); 26, 66-67, (1920)] were evidently 

 working on the colloid chemistry of bread at the same time as the 

 present writer who, unfortunately, has not had an oj)portunity of 

 seeing the complete papers. The general results obtained seem, 

 however, to bear out the conclusions reached by us in 1918, and 

 published in the British Baker in the following year. Ostwald and 

 Liiers have found that the chief differences between flour, dough, and 

 new and stale breads, are of a physical rather than of a chemical 

 nature, and these workers have studied each material separately as 

 a colloid, in much the same ^^■ay as we have done. The \ascosity of 

 various mixtures of flour and water, containing as much as 20 per 

 cent of flour, were made, and mixtures of wheat flour and water A\ere 

 compared against rye mixtures. It was found that rye mixtures 

 became more vi«cous, whilst wheat mixtures became thinner, on 

 standing, and that traces of acids greatly increased the viscosity of 

 the wheat mixtures, whilst sodium chloride appeared to reduce it. 

 One point of great importance was established, viz., that a flour of 



