151 



heat of about 600 degrees is required to raise the 

 vapour, which contains more and more acid, till 

 as last what comes over is as strong as what 

 remains behind. The less water there is, the 

 greater attraction this acid has for it ; so that at 

 the last a quantity of water remains united with 

 it, which it is not in our power t separate. The 

 process-, must be repeated till it is made of the 

 standard strength, which is known by its weight, 

 being to that of water as eighteen to ten. If we 

 require it very strong, the separation must be 

 very slow. 



If a drop of sulphuric acid falls on clothes, it 

 seems at first to have no effect ; but after a few 

 days the clothes break into a hole, which con- 

 stantly enlarges for a long time : the reason is, 

 that the acid takes some time to dissolve the 

 particles of the cloth; when it has dissolved 

 them, the action of it continues till the alkaline 

 salts it meets in the air destroys its effect. When 

 mixed with Florence oil, the sulphuric acid acts 

 upon the oil, so as to form a dark viscid sub- 

 stance, like tar, producing a considerable degree 

 of heat, and a vapour in smell resembling brim- 

 stone. The oil will afterwards dissolve in water. 



There are other oils on which it acts with 

 more violence, as the aromatic or volatile oils. 

 Thus, if to oil of turpentine (which is better for 

 this experiment when thick by standing) the 

 sulphuric acid is added, it boils with violence, 

 and very noxious fumes are produced. A black 



