270 KEPORTS ON THE STATE OF SCIENCE. 



B 5. — Liversion by Hydrolysed Salts. 



The salts of feeble bases are, to a certain extent, hydrolysed in 

 solution into free acid and base ; the free acid is able to invert cane 

 sugar. 



1864. This type of inversion was first noticed by Bechamp in the case of 



1878. mercuric chloride and was also observed by Pellet. 

 1884. E. Fischer inverted sugar by means of phenyl hydrazine acetate, 



1 QQo obtaining finally glucosazone ; Bach showed that the hydrochloride 



' and sulphate of hydrazine can also invert sugar. 

 1896. B^champ's observations were exteaded by Long, who found that 



cadmium chloride is particularly active in invertive power. 

 Quantitative estimations of hydrolytic decomposition by the sugar- 

 inversion method have been made by various workers and will be 

 considered in Section K. 



B 6. — Inversion by Solid Catalytic Ayents. 



Speranski showed that a clean glass surface does not alter the rate 

 1 SQO °^ inversion of sugar by acid. If, however, glass wool be present, 



■ a considerable amount of alkali is given up to the solution and 

 the inversion is slowed. ^ 



, QQ/. Rayman and Sulc observed that inversion occurs when cane- 



■ sugar solutions are in contact with finely divided metals, such s.s 

 Pt, Pd, Cu, Ag, Os, Ir, but more especially platinum, at 60, 80, and 100 

 degrees. At the same time they noticed that the solution became coloured 

 and acidic, owing to decomposition of the invert sugar. They afterwards 

 , jjQ- proved that formic and pyrolevulinic acids are produced mainly 



' from the levulose ; in the next year they concluded that the effect 

 1 QQfi produced by platinum is partly a catalytic oxidation and partly 



' a direct inverting action, for as soon as the platinum is added to the 

 solution acidity can be detected. 

 1 QOa. Plz^k and Husek have carried the proof of this explanation 



* still further by showing that platinum and palladium have no 

 invertive power when entirely free from their oxides. A sugar solution 

 may be boiled for hours with platinum black before hydrolysis sets in. 

 If, however, the metal be air-dried beforehand, it gets a coating of oxide 

 and becomes active, the activity depending upon the time of drying. 

 1 QHA Lindet, on the other hand, found that certain metals, such as 



' Cu and Pb, accelerate inversion, whilst others, such as Fe and Cd, 

 retard it. He supposed that small quantities of hydroxides are formed 

 from these metals, some of which are acidic and others basic towards cane 

 sugar. Pt, Ag, Au, &c., are said to have no action. Lindet also argued 

 that as sugar has a slight conductivity it should be sufficiently acidic to 

 hydrolyse itself in boiling solution ; he explained the non -occurrence of 

 inversion on boiling in glass vessels to be due to the fact that alkali 

 derived from the glass neutralises the acidity of the sugar itself. With 

 regard to the case of platinum, there can be little doubt that the action 

 -, ar.fr is an oxidising one, Vondracek having recently demonstrated that 



■ a specimen of platinum black, once used to effect inversion, loses 

 its activity towards a second sugar solution unless it be dried in air at 

 150°. Furthermore if a solution undergoing inversion in presence of 

 platinum be filtered from the metal, the action continues as a simple 



