56 



SIXTH REPORT — 1836. 



Experiments on the Combinations of Sulphuric Acid and Water. By 

 Thomas Thomson, M.D., F.R.S.L. andJE., SfC, Professorof Che- 

 mistry in the University of Glasgow. 



To obtain pure sulphuric acid, Nordhausen acid diluted with water 

 till its specific gravity was only 1'8375 was distilled in a retort till the 

 liquid remaining in the retort was precisely the same with that of the 

 last portion distilled over. This happened when the specific gravity 

 of the acid was 1-8422. It was then a compound of 



1 atom acid 5 



1 atom water l'\'25 



6-125 

 and its atomic weight 6-125. This acid, which was pure, (excepting 

 the presence of j^'o^th part of its weight of sulphate of lime) was 

 employed in the following experiment : 



1. Specific gravity of different atomic compounds of sulphuric acid 

 and water. 



These were obtained by mixing determinate weights of acid and water, 

 and taking the specific gravity of the compound. The following table 

 shows the result : 



From this table we see that the compound of one atom oil of vitriol, 

 with one, two, and three atoms water, has a specific gravity above 

 the mean, while the compounds of one atom oil of vitriol, with four, five, 

 six, seven, eight, and nine atoms water, are below the mean. In the 

 first case there is a condensation, but in the second an expansion, and 

 this expansion increases with the quantity of water. 



2. Heat evolved when an atom of oil of vitriol is mixed with from one 

 to nine atoms water. 



This was determined by pouring 1000 grains of oil of vitriol of 

 1-8422, upon the requisite quantity of water in a glass cylinder con- 

 taining the water, and stirring the mixture with a thermometer. The 

 thermometer rises with very great rapidity, and begins almost imme- 

 diately to descend, so that it is difficult to notice the highest point 

 to which it rises. The following table shows the result. 



