of Chemical Change. 127 



sulphate to produce the same rate of oxidation as the latter 

 acid alone. The values obtained would at first sight seem to 

 represent the absolute ratio of the dynamical equivalences of 

 these two acids ; but on considering the different changes 

 that take place in the two cases, such an inference cannot as 

 yet be drawn from this single reaction. When hydric chlo- 

 ride is added to a solution of ferrous sulphate containing free 

 hydric sulphate, the colour changes to a light straw-tint, 

 owing probably to the formation of some ferrous chloride. 

 When this solution is oxidized by potassic chlorate it becomes 

 after a time of an orange colour, due to the ferric chloride 

 formed ; so that, when experimenting with two solutions, one 

 containing hydric sulphate and the other hydric sulphate and 

 chloride, in the former case we have ferrous sulphate being 

 oxidized to ferric sulphate, and in the latter a mixture of 

 ferrous sulphate and chloride (having probably different 

 facilities of oxidation) converted into ferric sulphate and 

 chloride, also an oxidation of the hydric chloride. 



That ferrous sulphate in presence of hydric chloride is 

 partly converted into chloride may account for the fact that 

 in many cases when about 4 grms. H CI were employed the 

 observed and calculated values for y or t were found to differ, 

 the reaction seeming to undergo a gradual retardation. These 

 discrepancies, however, might arise from the difficulty of 

 making sufficiently accurate determinations of the iron by 

 permanganate in presence of hydric chloride. 



Various strengths of solutions were tried ; and the numbers 

 obtained for the ratio of H CI to H 2 S0 4 were invariably the 

 same within the limits of experimental error. 



The most complete series of experiments, contained in 

 Table III., were made with the following quantities of sub- 

 stances: — -5440 grm. iron, -1985 grm. potassic chlorate, and 

 various amounts of acid ; total volume 260 cubic centims. ; 

 10 cubic centims. of the permanganate equal to *0201 grm. 

 of iron. 



The numbers under " calculated ratio of dynamical equiva- 

 lence of H CI to HsSCV were obtained in the following- 

 way. It has been shown that b, or, in the first experiment 

 with 6 grms. H 2 S0 4 , 2357*5 is inversely proportional to the 

 amount of acid ; consequently to give the value 1664*8 it 

 would require 8*498 grms. H 2 S0 4 . But this number was 

 obtained with 4 grms. H 2 S0 4 and 2 grms. H CI. Hence by 

 exchanging 4*498 grms. H 2 S0 4 for 2 grms. H CI, the same 

 rate of change would be produced. Expressed in molecular 

 weights, 36*5 parts by weight of hydric chloride are equal to 

 82*1 parts of hydric sulphate in the dynamical sense. 



