The Oxidation of Cane Siujar. 223 



(ii.) Potassium permanganate : — 



As the solutions under ordinary circumstances 

 are so unstable, the ordinary pure salt was 

 used, and the solution constantly restandard- 

 ized with pure iron wire or recrystallized 

 ferrous ammonium sulphate. 



(iii.) Ferrous ammonium sulphate : — 



The salt obtainable was in obviously impure 

 crystals ; some was recrystallised for use as a 

 standard and found to compare satisfactorily 

 with pure iron wire. 



A larger quantity was purified by precipita- 

 tion with alcohol ; by this means the salt was 

 obtained in a readily soluble powder, which 

 was of about 99 per cent, purity. This was 

 of no consequence, however, for the solution 

 required restandardizing every two or thi^ee 

 days. 



(iv). A semi-normal sulphuric acid was employed and 

 prepared from the ordinaiy laboratory re- 

 agents. 



2. The contents of the flask in which the experiment was 

 conducted were quickly heated by immersing in Avater a few 

 degrees hotter than the desired temperature and cooled at the 

 conclusion of the experiment in cold water. 



In this way an uncertainty of not more than one minute was 

 introduced, and where the experiment continues for an hour or 

 over, this is neaflisjible. 



)ing the temperature constant to within 1°C. is liowever a 

 more serious consideration. 



For temperatures below 100°C. the liquid was contained in 

 ordinary stoppered lOOcc. flasks which were allowed to rest on 

 a perforated shelf in a large constant level water-bath. The 

 water was kept at the desired temperature by heating with a 

 bunsen burner. 



In my later experiments on the velocity of the reaction 

 eflScient circulation of the water was produced by means of a 

 central vertical cylinder surrounding a screw propeller worked 

 by a small water motor. 



