on the Rate of Chemical Change. 325 



It was stated that the few experiments that were made to 

 determine the form of this temperature function seemed to 

 indicate that/(0) = 2 , or that the rate of change varies as the 

 square of the temperature. 



This reaction has again been made the subject of investi- 

 gation , with regard to temperature, and the results obtained 

 are comprised in the following tables. 



The mode of performing the experiments has already been 

 fully given in several papers in this Journal, so that it will 

 be sufficient merely to give the strengths of the solutions 

 employed in the work. Each experimental solution consisted 

 of *5637 gram iron (Fe /7 ) as sulphate, '2057 gram KC10 3 , 

 and 3*099 grams free hydric sulphate, made up to a volume 

 of 260 cubic centims. contained in a glass flask and main- 

 tained at the required temperature in a large water-bath. 

 The course of the oxidation was observed by withdrawing 10 

 cubic centims. of the solution, and titrating with perman- 

 ganate at indefinite intervals of time, to determine the equa- 

 tion y(a + £) = b; y being cubic centim. permanganate and t 

 time in minutes. Two, and in many cases four, experimental 

 solutions were employed at each temperature, and the values 

 for a and b that are given are the means of these. Every 

 precaution was taken to. keep the temperature of the mea- 

 suring pipettes, permanganate, &c. the same as that of the 

 experimental solution, — the thermometers employed being 

 very fine ones, by Negretti and Zambra, divided to tenths, 

 on which *02° could be read easily; and in every case where 

 an experiment fluctuated by so much as ±'1° C, the results 

 were rejected. 



Although the experiments tabulated below are only com- 

 prised between the narrow limits of 10° and 32° C, it was 

 found that outside these extremes the results were liable to 

 be vitiated by several sources of error. Below 10° C. the 

 progress of the oxidation was so slow that during the long 

 period that the experiments had to be continued there was 

 liability of atmospheric oxidation taking place; besides, a small 

 error in the permanganate titration made a comparatively 

 large one in the time, whereas above 32° 0. the speed was 

 much too rapid to obtain accurate measurements. Between 

 these narrow limits of temperature the rate of oxidation 

 increases over sevenfold. 



In the figure, the course of a few of the experiments are 

 plotted from the experimental numbers, and these curves 

 show at a glance the great differences in the rates of oxida- 

 tion at the various temperatures. 



