Combination of Sulphuric Acid and Water. 255 



than the mean. The condensation is greatest when 1 atom 

 of oil of vitriol combines with 1 atom of water amounting 



to — - that of 1 atom oil of vitriol with 2 atoms water is 

 rr-., while that of 1 atom oil of vitriol with 3 atoms water 



is only ^. 



When we combine 1 atom of oil of vitriol with 4, 5, 6, 7, 

 8, 9 atoms water the specific gravity of the compound is 

 below the mean, so that the bulk increases instead of 

 diminishing, and this increase augments with the number 

 of atoms of water. The following table shows the amount 

 of the expansion. 



From this remarkable change from condensation to ex- 

 pansion it is reasonable to infer, that a change takes place 

 in the nature or intimacy of the combinations. The com- 

 bination of 1 atom oil of vitriol with 1, 2, 3 atoms water is 

 probably more intimate than the remaining 6, which are 

 accompanied by expansion. Accordingly we shall find, 

 that most of the heat evolved, when oil of vitriol and 

 water are united, is the consequence of the union of 1 atom 

 oil of vitriol with 1 , 2 or 3 atoms water. 



These experiments were repeated two or three times; 

 but the specific gravities were found always to vary, some- 

 times in the second decimal place, and always in the third. 

 This I ascribe to the great avidity of oil of vitriol for 

 moisture. The experiments related in this paper occupied 

 a considerable time, about two months of the summer of 

 1836. The first part of this summer was very dry in Glas- 

 gow, and the latter part very wet. Now, during the weigh- 

 ing of the oil of vitriol (which occupied at least 5 minutes) 

 it was of necessity exposed to the atmosphere. Hence, it 

 would imbibe moisture, and more would be imbibed when 

 the air was damp than when it was dry. No doubt the 



