322 THE SCIENTIFIC PAPERS OF 



a larger amount of crystallizable sugar if the direct application of 

 heat in the vacuum pans had been resorted to exclusively. 



It might be urged that such an amount of heat could not have 

 been obtained, owing to the larger consumption of fuel which 

 would have been requisite ; but there was a process now in course 

 of trial, partly suggested by himself, to evaporate entirely by 

 vacuum pans, and at the same time to economise heat by forcing 

 the steam generated at low pressure within the vacuum pan 

 mechanically into the tubes surrounded by the juice. 



The main feature of the paper was the substitution of sul- 

 phurous acid for charcoal in removing the colouring matter. If 

 sulphurous acid could be applied without practical drawbacks, 

 great saving must undoubtedly arise, because animal charcoal 

 was an expensive substance, and involved the employment of 

 complicated apparatus to revivify it for repeated use. But the 

 question arose whether in using the sulphurous acid method a 

 portion of the crystallizable sugar was not converted into un- 

 crystallizable, or grape sugar ? It was a well-known fact that 

 if sulphuric acid was put into a solution of cane sugar, its mere 

 contagious action, so to speak, would convert an indefinite amount 

 of the solution into uncrystallizable, or grape sugar, which, 

 though very similar as to chemical constitution, was of a much 

 less sweetening character. It was doubtful whether the sul- 

 phurous acid was always free from sulphuric acid, particularly if, 

 as was suggested, oxydising agents, such as peroxide of manga- 

 nese, were also employed. An increase of grape sugar would not 

 necessarily imply a diminished yield, because when the solution 

 came to a certain consistency it might solidify. He would in- 

 quire whether in the sugar prepared at the Aba mills there was 

 not a proportion of uncrystallizable, or grape sugar precipitated 

 with the crystallizable, or cane sugar ? He did not believe in 

 the theory put forward that galvanic action would be set up 

 between the charcoal and the colouring matter. The conditions 

 of sugar solution were totally at variance with what might be 

 expected in a galvanic battery, where two conductors of different 

 affinity for oxygen were brought into metallic contact while 

 immersed in acidulated water. 



In regard to the experiments which he had referred to as 

 having been conducted for effecting the concentration under a 



