Sulphate of Copper, or Blue Vitriol

According to my specimens, which I have had many years, this is found in those rocks which are usual in North Wales, in which Cubic Pyrites so much abound, and is occasionally adulterated by the Iron, It is most pure when nearly deep blue with a greenish cast; but is sometimes lighter coloured, as figured. It is leas soluble than Sulphate of Iron, requiring four times its weight of cold water, and twice its weight of boiling water for solution; it is also styptic to the taste. It may be artificially procured of a vivid and rich bluej but always having a greenish cast.

The upper figure gives the most usual appearance of it upon the rock. The specimen figured below was, when first gathered, of the beautiful blue cast of the fresh broken timer part; probably some Oxide of Iron is the cause of the outward change of colour, which, however, doest not penetrate far into it. The best Crystals are formed artificially. The primitive form is a parallelepiped with oblique angles:—see the bottom outline. Spec. Grav. 2.19.

Analysis by Mr. Kirwan:

Although water is necessary to this substance, as well as to the Sulphates of Iron and Zinc, and might be considered in sufficient proportion to make them aqueous species; yet we rather think the specific appellation best given from the Sulphuric Acid, as most essential to their nature.