150 Chemistry. [Lecture 29. 



is sufficiently strong : for the sulphuric is one of 

 those acids which are called^mZ, because they 

 do not, like vinegar, rise in vapour with heat. 

 The sulphuric acid, when pure and as strong as 

 possible, is clear and heavy, its specific gravity 

 being to that of water as eighteen to ten. From 

 its having less fluidity or mobility, and an ap- 

 pearance of sluggishness, it has been improperly 

 termed oil of vitriol. It is not volatile, and 

 being more fixed than water, emits no fumes 

 under the ordinary heat of the air, and there- 

 fore has no smell. Its violent attraction for 

 water often breaks the vessel in which they are 

 mixed, by the heat. It also attracts from the 

 air on the first day one-third of its weight of 

 water, and in six days more than its weight. 

 This depends, however, on a large surface be- 

 ing exposed to a moist air. Its attracting more 

 copiously at first, shows that the attraction of 

 the acid for water diminishes as it approaches 

 nearer saturation. When we add water to di- 

 lute this acid, it sometimes becomes milky, and 

 a whitish powder falls to the bottom. This 

 phenomenon happens on account of its impurity, 

 for the pure vitriolic acid when mixed with 

 pure water has no such appearance. The water 

 may in a great measure be separated by distil- 

 lation, but not in open vessels, as we should then 

 lose part of the acid. When put into a retort, 

 the first vapour that rises is pure water. In pro- 

 portion as the water diminishes, a more violent 



