744 AMYLACEOUS AND SACCHARINE SUBSTANCES, 



is C 12 H 10 O 10 , and of two dextrinates of lead dried at 356, 

 C 12 H 9 O 9 + PbO, and C 12 H 9 O 9 + 2PbO, so that dextrin is 

 identical in composition with amidin, both when free and in 

 combination. Both of the dextrinates of lead retain 1 eq. of 

 water, when dried at inferior temperatures. A dextrinate of 

 barytes, prepared by Payen by means of a solution of anhydrous 

 barytes in wood spirit, and strongly dried between 356 and 

 374, gave C 12 H 9 O 9 + BaO,HO. 



When dry starch is heated in an oven it becomes brown and 

 soluble in cold water. It then forms British gum, which cor- 

 responds in properties with dextrin. 



Diastase. This is a remarkable substance observed by Payen 

 and Persoz in grains and seeds, but only after germination, and 

 in the tubers of the potato near the places from which the 

 shoots proceed. The production of diastase is the principal 

 object of the malting of grain or permitting it to germinate, and 

 has an important influence upon the changes which occur in 

 the starch of grain in brewing. Diastase is prepared by moisten- 

 ing freshly germinated barley with half its weight of cold water, 

 and submitting it to pressure, by which a viscid liquid is 

 obtained. This liquid is filtered and then heated to 158, 

 which causes the greater part of an azotised or albuminous 

 matter existing in the liquid to be coagulated and separated. 

 The liquid after nitration is mixed with a sufficient quantity 

 of alcohol to precipitate the diastase and retain in solution the 

 colouring matter, sugar and foreign azotised matter present. 

 The precipitated diastase is washed with alcohol, dissolved again 

 in water and thrown down by alcohol two several times, 

 for the purpose of purifying it (An. de Chi. &c., liii, 73). 

 When dried it is a white solid amorphous substance, soluble 

 in water, but insipid, and not precipitated by subacetate of 

 lead. It contains nitrogen, and has some analogy to gluten, 

 but has not been obtained in a state of sufficient purity for 



produced which follow a certain order, if the plane of polarisation is turned from 

 left to right. Tt is by the order of these colours, that a liquid is said to polarise 

 light to the right or to the left. The solution of starch polarises to the right and 

 that of dextrin cousiderably more so in the same direction. While a solution 

 of cane sugar produces the succession of colours in an inverse order, and is said 

 therefore to polarise to the left. The progress of chemical changes may thus 

 often be observed in a solution of starch, the juices of plants and other organic 

 fluids. 



