PREFACE.

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tnixture, kept perfectly dry, continues unaltered for years :on being moistened with water, it grows spontaneouslyhot in a few hours, and if the quantity is large, it evenr bursts into flame, with such commotion, as has induced

many to ascribe earthquakes and volcanoes to this cause.During this action, the acid is transferred to the iron ; andthe inflammable matter, before combined with it, escapesinto the air. The combination of the acid with the ironforms the green vitriol or copperas of the /hops; a salt ofa strong taste, and of easy solution in water, though thequantity of iron in it is very far greater than that of theinflammable matter by which, in the form of brimstone,the miscibility of the acid with water was destroyed.

To the green solution ot the vitriol, if some vegetableashes, or the earth called magnesia, be added, the iron fallsto the bottom, considerably altered, in form of ochre or rust,,deprived of its attractive power to the magnet, and of allits metallic properties, which however are easily restored'by exposing it to the fire in mixture with a little charcoalpowder. In room of the iron thus thrown out from theliquor, the acid attacks the vegetable earth or magnesia;and though with one kind of earth, as we have seen above,it forms an insipid and indissoluble concrete; with boththese earths it composes a bitterish salt which dissolveseasily, and which, at least when magnesia is made use of,is the fame with that of the purging mineral waters..

If to the solution of this fait we add a volatile alcalinelalt, the penetrating smell of the alcali is suppressed in aninstant, the acid uniting with the alcali into a new com-pounds

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