A substance which is very abundant in nature, and is now denominated, according to the new chemical arrangement, the sulphate of lime. It forms immense strata, composing entire mountains; it is found in almost every soil, either in greater or less quantities; it is contained in the waters of the ocean, and in almost all river and spring water. In these its presence is the cause of the quality termed hardness, which may be known by the water being incapable of forming a solution of soap, the sulphuric acid seizing on the alkali of the soap, and the oil forming a compound with the lime. Sulphate of lime is insipid, white, and soft to the touch; water will not hold a five-hundredth part of it in solution. Exposed to heat it appears to effervesce, which phenomenon is caused by the expulsion of water; it becomes opaque, and falls into powder. This powder, when its water has been driven off by the application of a red heat, absorbs water rapidly, so that if it be formed into a paste with water, it dries in a few minutes.

In this state it is called plaster of Paris, and is employed for forming casts, and for a variety of purposes in the art of statuary.