CHAP. I.] ' DIASTASIMETKY.' 59 



easy to calculate the weight of starch which has been brought to 

 the achromic point; we have merely to divide D by 100 to obtain 

 the weight of starch in grammes, or fractions of grammes ; thus in 



QO 



the above experiment -7 = 0'83 grms., being the weight of dry 



starch converted. 



In the method of diastasimetry which has been described, almost 

 in the very words of its originator, Dr William Roberts, the reaction 

 which is selected as the final reaction depends upon the disappear- 

 ance of all dextrins which are coloured yellow by iodine, the solu- 

 tion containing only maltose and a dextrin which give no reaction 

 with this reagent. Under the same circumstances as to temperature, 

 the reaction proceeds with perfect regularity, and so as to admit of 

 very accurate observations. 



" Probably," as remarks Dr Roberts, " the most accurate mode 

 of estimating the activity of a diastatic solution is to ascertain the 

 amount of sugar produced when a given quantity of the solution is 

 made to act on a given volume of a standard starch mucilage, for a 

 fixed time, and at a given temperature. This method has already 

 been recognized by Messrs Brown and Heron, in their paper, ' On 

 the Transformation of Starch by Malt Infusions/ Kyeldahl has 

 developed the method to a further point, and has used it to measure 

 the comparative activity of malt infusions and of saliva." 



The amount of sugar was determined in the experiments referred 

 to by estimating the amount of a standard solution of a cupric salt 

 which could be reduced by a known volume of the saccharine liquid. 



The diastatic value may also be judged of in a similar manner 

 by determining the rotatory power of the liquid which has been 

 subjected to the action of the enzyme; in order to carry out this 

 method, it would be necessary to separate the dextrins from the sugar 

 formed, by the action of alcohol, 



