acid. The usual formula for the per cent of cane sugar may, there- 

 fore, be used with the new factor 141.7 when the inversion is carried 

 out by the use of invertase, namely: 



O _ T 



Per cent of cane sugar=- - 



THE INFLUENCE OF ACIDS AND ALKALIS ON THE ACTIVITY OF 



INVERT A SE. 



Invertase acts only in an acid medium, and the slightest alkaline 

 reaction stops its action instantly. Weak alkalinity does not destroy 

 it, however, for if the acidity be restored the invertase resumes its 

 original activity. But it is quite important that the medium be only 

 weakly acid, for invertase is rendered inactive and even destroyed by 

 acidities above hundredth-normal hydrochloric. As this acidity is 

 itself rather weak, it seems best to avoid the use of strong mineral 

 acids entirely in preparing the sugar solution for the action of inver- 

 tase, and to use in their place a weak organic acid such as acetic, for 

 invertase is quite active in acetic acid of 5 per cent strength. 



In the accompanying figures there is given the measured activity of 

 invertase in solutions of hydrochloric acid and of acetic acid. These 

 activities were found by mixing, at 30 C., 100 cc of 0.2 normal 

 (approximately 7 per cent) cane sugar solution with 5 cc of the appro- 

 priate strength of acid and 5 cc of a stock invertase solution, and 

 measuring the velocity-coefficient (k) of the resulting inversion by the 



7 r> _ -p 



usual formula It -. log -^ ^ where R is the initial rotation of the 



t JLl -/ioo 



solution, j??oo the value after complete inversion, R the rotation at the 

 time t (expressed in hours), and log the common logarithm. Care was 

 taken to make the samples alkaline before each reading of It in order 

 to stop the action of the invertase and complete the mutarotation of 

 the invert sugar. 



Figure 1 shows that invertase is active within only a very small 

 range of acidity when the latter is due to a strong acid like hydro- 

 chloric, which is almost completely dissociated in solution, but if a 

 weak acid like acetic is used, its dissociation is so slight that quite strong 

 solutions can be used without bringing the actual acidity (i. e., hydro- 

 gen-ion concentration) up to a strength which is inimical to the action 

 of invertase. As it would be difficult in practical work to adjust the 

 acidity of the solutions very accurately, it is recommended that the 

 solutions be all made acid to litmus with acetic acid, as even a con- 

 siderable excess of acetic acid will do no harm. 



DIRECTIONS FOB MAKING THE ANALYSIS. 



Dissolve 26 grams of the substance to be analyzed for cane sugar in 

 water, clarify with the usual substances (neutral or basic lead acetate 

 or alumina cream or kaolin) and make up to 100 cc volume at 20 C. 



Cir. 50. 



