3^0 On the Determination of the [Nov. 



calorimeter was become stationary, we determined the quantity 

 of gas which passed through the serpentine while that tempera- 

 ture rose a certain given number of degrees, setting out from a 

 given point, and likewise the time necessary to produce this 

 effect. We employed the results of these experiments to calcu- 

 late the specific heats of the gases experimented upon, setting 

 out from this simple principle, that the specific heats, cceteris 

 paribus, must be inversely as the quantities of gas necessary to 

 produce the same elevation of temperature. In order to make 

 accurate experiments according to this principle, it was necessary 

 to take certain precautions, and to make some corrections on the 

 results, which it will be proper to point out. 



Philosophers have long been of opinion that the quantity of 

 heat disengaged during the combustion of different substances 

 might be determined in this manner ; but it was necessary to 

 contend with a cause of error, which proved very injurious to 

 the accuracy of the results. In proportion as the calorimeter 

 became hot, the air and the surrounding bodies deprived it of a 

 portion of its heat. Hence the whole heat of the burning body 

 was not indicated by the rise in the temperature of the calori- 

 meter. It was necessary to include the heat lost during the 

 process, and this was very difficult. 



In order to get rid of this inconvenience, Count Rumford 

 conceived the hippy thought of beginning the experiment not 

 at the temperature of the surrounding air, but a little below it, 

 and to allow the experiment to continue till the calorimeter was 

 heated as much above the surrounding air as it had been below 

 it at the commencement. By this method he made the heating 

 of the calorimeter almost independent of the surrounding air. 

 During the first part of the process the air would communicate 

 heat to the calorimeter : but during the second part the calori- 

 meter in its turn would give out nearly as much heat to the air 

 as it had received from it at first. 



According to this principle, we sunk the temperature of our 

 calorimeter about 10° Fahrenheit below that of the air of the 

 roo:n ; and causing a current of hot gas to pass through it, we 

 did not begin our experiment till the temperature of the calori- 

 meter was within 4° of that of the air of the room. We then 

 began to reckon the number of cubic inches of gas necessary to 

 raise the temperature 8° higher than the initial temperature. By 

 this method we made two experiments at once ; one which gave 

 us the quantity of gas necessary to raise the calorimeter 8° ; 

 another which gave that which was necessary to raise it the 4 

 intermediate degrees. It is difficult to say which of these deter- 

 minations led us to the most exact conclusions : the difference 

 between them was never considerable, as may be seen by the 

 table of our results. 



