290 INVERTASE. [CH. XVI 



The diastatic power of the extracts will be proportional 

 to the numbers of c.c. of each which will ' convert ' a 

 given weight of soluble starch in a given time under similar 

 conditions : e.g. if in one set of experiments ' conversion ' is 

 just complete in B, (2 c.c. extract) and in another in D, 

 (4 c.c. extract) the diastatic power of the first extract is 

 twice that of the second. 



Another method is to allow equal quantities of the 

 extracts to act upon excess of solution of soluble starch for 

 one hour at 50° — -55° C, and then estimate the ' reducing 

 sugars' produced. 



At the end of one hour the mixtures are concentrated 

 on a water bath, after first rapidly heating to 100° C. to 

 stop further action, and the starch and dextrins precipi- 

 tated together by excess of alcohol. 



The reducing sugars are estimated in the filtrate, after 

 distilling off the alcohol and taking up the residue with 

 water, by Fehling's (or other suitable) solution (see p. 267). 



The reducing power of the extracts used must be 

 determined in each case and subtracted from the total 

 reducing sugars found. 



The diastatic power of the extracts will be proportional 

 to the amounts of reducing sugars formed by their action 

 on soluble starch. 



Invertase. 



(1) Filter off some of the water in which active yeast 

 is suspended, by adding some ' paper pulp ' and filtering 

 through asbestos : [it is not very easy to completely remove 

 yeast by ordinary filtration]. 



