ON THE HYDROLYSIS OF SUGARS. 271 



unitnolecular change ; further proof of the presence of acid can be deduced 

 from the electrical conductivity of a solution so treated. 



It is, therefore, not to be credited that platinum or palladium black 



1900. ^^^ invert cane sugar catalytically. Sulc, indeed, has shown that 



palladium has a very unfavourable effect, diminishing the hydro- 



lytic activity of hydrochloric acid towards cane sugar, maltose, raffinose 



and also methyl acetate. 



It is permissible to question the validity of the conclusion arrived at 

 1906 ^^ Neilson that platinum black can hydrolyse starch, salicin and 

 amygdalin at 40°. 



B 7. — Hydrolytic Activity of Light. 

 Raoult claimed to have established that six months' exposure to H»ht 

 1871. ^^^ brought about the inversion of a sterile solution of cane sugar, 



whilst a second sample, kept in the dark, was not inverted. A 

 trace of acidity in the one specimen would account for the result obtained : 

 1875. "^ ^*^*' Kreusler, on repeating the experiment several times with 



pure material, failed to obtain any inversion at all. 

 1883. Gladstone and Tribe also showed that neither light nor air, alone 



or in conjunction, can change cane sugar solutions when left for 

 seventeen months at room-temperature. Raoult's experiment was also 

 repeated and a negative result obtained. 

 1886. Duclaux, whilst agreeing that light alone cannot invert cane 



sugar, maintains that the velocity of inversion by acids is lower in 

 absence of light. 



1900. . ^^^\°*' *^<'; claims to have demonstrated that light, especially 

 violet light, aids the inversion of sugar by a mineral acid. As no 

 thermostat was used in his experiments, the small difference observed 

 may well have arisen as a consequence of the slightly lower temperature 

 of solutions kept in the dark. 



C. — Methods of Measuring the Velocity of Inversion. 



01. — Polarimeter Method. 



The velocity of inversion was first successfully measured by Wilhelmy 

 by means of the polarimeter ; the majority of subsequent observers have 

 followed his example. The change in the optical rotation on passing from 

 cane sugar ([„]„= + 66°) to invert sugar ([«l^=-28°) is so large that it 

 is not difficult to obtain accurate measurements even with a compara- 

 tively rough polarimeter. The chief error in most of the researches is 

 probably that arising from fluctuations of temperature. 



C 2.— Titration Method. 

 Lowenthal and Lenssen appear to be almost the only investigators 

 1862 ^*^° '^^^® "^®^ *^6 cumbersome method of titration with FehJinff's 



Solution. 



3. — Volume Method. 



The inversion of sugar, accompanied as it is by the chemical com- 

 bination of part of the solvent water and by the substitution of two 

 molecules of monose for one of biose sugar, gives rise to a diminution in 



