272 REPORTS ON THE STATE OF SCIENCE. 



the total volume of the solution. This contraction during inversion was 

 noticed by Graham. 



, j3^Q Dubrunfaut measured the rate at which the contraction occurs 



' and hence calculated the rate of inversion. He imagined the 

 change to follow a parabolic law instead of a logarithmic one. 

 , Q_.^ Chancel measured the total amount of contraction when sugar is 



converted into invert sugar by a trace of sulphuric acid at 100° 

 and proposed to use the method for estimating cane sugar. 

 -, Q^, More recently Duane, in America, unaware of previous work, has 



succeeded in obtaining fairly good velocity constants by observa- 

 tions of the volume change of the solution undergoing inversion. 



C 4. — Osmotic Pressure Methods. 



As each molecule of cane sugar is converted into two molecules of 

 monose, the total number of dissolved molecules will increase. Hence 

 the boiling and freezing points of the solution will change, 

 isqi -^y determining the boiling-points at intervals Trevor and 



Kortright were able to calculate the velocity constant with a fair 

 degree of accuracy. The method, liowever, is of very limited application. 

 , j,„Q Kahlenburg, Davis and Fowler, on the other hand, made deter- 



minations of the freezing-point to measure the inversion velocity 

 in presence of coloured materials, which prevent the use of the polari- 

 meter. Test experiments showed that the same value for the velocity 

 constant was obtained by polarimeter and freezing-point methods. 



C 5. — Refractive Index Method. 



A change in the refractive index of the solution accompanies the 

 inversion of cane sugar. 



, q|-.^ Duane has made measurements of the velocity with the aid of 



this property, using a photographic method to determine the index 

 of refraction from time to time. 



C 6. — Conductivitij Method. 



Seeing that water molecules are used up during the hydrolysis of 



1 QOfi (i^T^^ sugar, the ratio acid : water must change. Bevan has recently 



■ shown that this change is accompanied by a slight decrease in the 



conductivity of the acid ; by measuring the resistance of the solution 



from time to time, he was able to follow the course of the hydrolysis. 



D. — Influence of the Nature of the Acid employed. 



Biot foresaw that comparative experiments with molecular amounts of 

 divers acids would yield results of great interest but he was unable to 

 follow the subject up. 

 , ani) Lowenthal and Lenssen showed that the velocity of inversion 



"■ depends entirely on the acids used and were of the opinion that 

 weak acids like acetic acid cannot invert cane sugar at all. 

 iRsa. Battut, however, arrived at the astonishing conclusion that 



acetic, tartaric and sulphuric acids are equally active towards 

 cane sugar. 



