382 Mr. J. J. Hood on the Laws of Chemical Change, 



In nil the experiments given in this paper there is one 

 special point to which I wish to draw attention; and that 

 is that only two observations are taken to find the neces- 

 sary constants ; if these had been calculated for each pair of 

 observations and the means taken, better agreement with theory 

 would doubtless have been obtained ; but such a procedure 

 is apt to throw doubts on a theory, as to which, if it were true, 

 one observation should be as good as another for determining 

 the constants, unless large errors were suspected. 



Before selecting those observations which were to be taken 

 for the constants, the first few were laid off graphically, and 

 those which seemed to be the most regular were chosen. 



Influence of Temperature. — Chemical decompositions are all 

 more or less influenced by heat, the effect being an accelera- 

 tion of the rate of change ; but it is very probable there is a 

 point at or below which temperature no change can take 

 place, as in the many cases where an acid has not action on a 

 body at the ordinary temperature, while on heating to about 

 100° C. change goes on briskly. 



The relation of the rate of change to the temperature and 

 the point of zero action are possible to be discovered by the 

 foregoing experiments in a simple manner. 



It has been shown that the rate of change is expressed by 

 the equation 



and if it be proportional to an unknown function of the tem- 

 perature /(#), 6 being degrees Centigrade above the zero- 

 point, so that 



integrating, 



writing it in the usual form, 



b=y(a + t), 



b and a being determined experimentally. If for a second expe- 

 riment under exactly the same conditions, but temperature 

 differing by n° C, the equation is found to be 



V=y(a! + t), 

 we get at once the relation 



b _ f(0 + n) 



b>~ f(6) ' 



