Combination of Sulphuric Acid and Water. 257 



The greatest rise of temperature took place when 1 atom 

 of oil of vitriol was mixed with 2 atoms water. But 1 atom 

 oil of vitriol with 1, 2, 3 and 4 atoms water occasioned con- 

 siderable evolution of heat. 



But in order to be able to judge of the real source of this 

 heat, it was necessary to make another set of experiments. 

 I prepared nine mixtures of oil of vitriol and water in the 

 proportions of 1 atom oil of vitriol, and 1, 2, 3, 4, 5, 6, 7, 

 8, 9. These were put into nine cylindrical glass jars 

 covered each by a small flat glass. The acid in each 

 weighed 1000 grains. They were left 24 hours in order to 

 acquire the temperature of the room, which happened (in 

 most cases) to be 63°. Then a quantity of water, equivalent 

 to one atom, was mixed with each, and the augmentation 

 of temperature was noted. The following table exhibits 

 the result of these trials : 



It is obvious that the greatest rise of temperature takes 

 place when 1 atom of oil of vitriol is mixed with 1 atom of 

 water. The acid of the strengths indicated in Nos. 2, 3 

 and 4, also produced a considerable augmentation of tem- 

 perature, but rapidly sinking, till the increase, when an 

 atom of the weakest acid of all was mixed with an atom of 

 water, was only 3 degrees. 



If we calculate what the specific gravities of the above 

 mixtures ought to be, on the assumption that no alteration 

 in the bulk takes place by the union of the acid and water, 

 and compare it with the actual result of experiment, we 

 shall find that an expansion takes place in all cases except 

 the first, when an atom of oil of vitriol is combined with an 



VOL. IV. s 



