Department of Chemical Research. 



407 



The curves are drawn upon the same scale as those of the 

 weak solutions of the above-named acids. 1st. They are very 

 greatly different from those of the halogens, and show very 

 much smaller degrees of electromotive force. 2nd. Their 

 differences from those of hydrochloric, hydrobromic, and 

 hydriodic acid of the same range of degrees of strength are 

 also quite conspicuous. And 3rd. They are sufficiently unlike 

 to be characteristic of each substance and to be clearly dis- 

 tinguishable from each other. The solutions employed were 

 too weak to fully show the characteristic forms of the curves ; 

 the degrees of strength were chosen chiefly to enable the 

 curves to be compared with those yielded by the halogens and 

 by their acids. 



4. Curve of H 2 S0 4 at 60° CL 



The range of degrees of strength of the solution was the 

 same as in the previous case, viz. from *001 to *01 grain of 

 the substance in 155 grains of water. 



Volta. 



Fig. 6. 

 Curve of H 2 S0 4 at 60° C— Weak Solution. 



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By comparing the curves obtained at the two different 

 temperatures, we find that a rise of temperature caused a 

 general increase of electromotive force, greatest at the com- 

 mencement, and quite sufficient to distinguish the one curve 

 from the other. The difference would probably be much 

 greater with stronger solutions (compare figs. 9 and 10 of 

 KBrat 18° C. and 60° C). 



