25G Dr, Thomas Thomsons Exjieriments on the 



highest specific gravities in all cases approached nearest 

 the truth. But as I was obliged to strike a mean in all the 

 other parts of the investigation, I thought it better to 

 strike a mean also in the specific gravities. Because, by 

 so doing, I exhibit the specific gravities of the very acids 

 which correspond with the specific heats and evolutions of 

 heat given in a subsequent part of this paper. No doubt 

 in some cases (perhaps in all) the acid may be a little 

 weaker than I have stated ; but the error must be too 

 small to affect the correctness of the general results. 



2. Heat evolved when an atom of Oil of Vitriol is mixed with 

 from one to nine atoms of Water. 



To determine this point, I sometimes mixed 24 cubic 

 inches of oil of vitriol w4th the quantity of water necessary 

 to constitute the number of atoms required ; but in general 

 I took 1000 grains of oil of vitriol, which was previously 

 weighed in a glass cylinder, and poured into a small glass 

 cylinder containing the requisite quantity of water. The 

 bulb of a thermometer was previously inserted into the 

 water. It had a scale ascending to 320°, which I knew 

 by previous trials to be sufficient for my purpose. The 

 mixture was stirred with the thermometer and the tem- 

 perature noted. It was then set aside for 24 hours, covered 

 with a glass plate; and the specific gravity was deter- 

 mined next day. 



The following table exhibits the weights of oil of vitriol 

 and water used in each experiment, together with the rise 

 of the thermometer or the heat evolved. 



Heat 

 evolved 



185° 



219 



208 



203 



178 



163 



148 



139 



129 



