236, 237. GLUTEN, ETC. 243 



In its other properties it agrees fairly well with gliadin. (Compare 

 also 237.) 



236. Gluten. Glutencasein, glutenfibrin, gliadin, and mucedin are 

 the principal constituents of the so-called gluten which possesses 

 such importance as a food. An estimation of total gluten is 

 generally made by rubbing down 10 to 20 grams of the, meal to 

 a paste with water, transferring to a fine linen cloth, and washing 

 with distilled or rain-water until the washings, on standing, deposit 

 only traces of starch. The mass is then pressed, scraped from 

 the cloth, and dried on watch-glasses, finally at a temperature of 

 115 to 120 ; it should then be powdered and dried again until 

 the weight is constant. In this method of estimating gluten it 

 will be found advantageous to add a weighed quantity (1 to 

 2 grams) of purified bran, the weight of which is afterwards, of 

 course, to be deducted from that of the total gluten. * 



According to Benard and Girardin, 2 the amount of gluten found 

 varies if the mixture is allowed to stand before washing with 

 water. It would be advisable to begin washing about three hours 

 after mixing the meal with water. 



237. Substances dissolved by Dilute Alkali, not precipitated by 

 Acid and Spirit. In estimating metarabic acid and albuminous 

 substances sparingly soluble in water, as directed in 103 and 206, 

 it will not unfrequently be observed that the total substances ex- 

 tracted by dilute alkali are considerably in excess of those pre- 

 cipitated by acid and alcohol. A part of the former, therefore, 

 must still remain in solution, and will be recovered, together with 

 acetate of sodium, by evaporating the filtrate ( 107). We may 

 expect to find here the constituents of gluten (including gliadin) and 

 products of their decomposition. After distilling off the majority 

 of the spirit, they might be precipitated with acetate of copper, 

 and estimated as directed in 231. 



The substances not precipitated by this reagent are probably 

 allied to, or derived from, vegetable mucilage; they may be 

 estimated by removing the excess of copper with sulphuretted 

 hydrogen, evaporating to dryness and weighing, deducting the 

 acetate of soda present. 



With regard to the latter, I may observe that it cannot be cal- 

 culated from the amount of soda used, but must be estimated by 



1 Compare Archiv d. Phann. cxcv. 47, 1871. 



2 Journ. de Phann. et de Chim. [5], iv. 127, 1881. 



162 



