HYDROUS SULPHATE OF LIME, OR GYPSUM. 



ei 



The sulphate of barytes is often used to aduUerate white lead ; nor is it easy, without a 

 chemical examination, to detect its presence in the mixture. As a paint, the mixture answers 

 equally well in most cases ; but it can, and should, be sold at a much cheaper rate than the 

 pure white lead. 



Other materials, which abound in this State, have recently been introduced as lithic paints, 

 as soapstone and serpentine. Prof. Hitchcock states that these substances are ground with 

 whale oil ; and in Connecticut, where they have been manufactured, they are sold for five 

 dollars per hundred pounds. They answer a good purpose as a basis for common paints, 

 especially for the roofs of houses.* 



CALCAREOUS MINERALS. 



Fig. 13. 



Under this general head, I shall notice Gypsum, Marble, Hydraulic or Water Limestone, 

 and Marl ; all of which occur very abundantly in this State. 



HYDROUS SULPHATE OF LIME. Thomson. 



Gypsum. PhUUps. — Chaux sulphat^e. Hauy. — Sulphate of Lime. CUaveland. — Prismatoidal Gypsum, or Common Gyp- 

 sum. Jamamt. — Prismatoidisches Gyps-Haloid. Mohs. — Gypse. Beudant. — Gypsum. SAepord and JJana. — (Includes 

 Selenite, Alabaster, Earthy Gypsum, and Plaster Stone.) 



Description. Colour snow-white when pure ; but it is often red, yellow, blue and grey. 



When crystalhzed, it is fohated ; but it occurs also fibrous, 

 granular and compact. The foliated varieties are called Se- 

 lenite, from their fine white colour. They split into thin leaves 

 parallel to the base of a right oblique prism, the faces of which 

 are inclined to each other at angles of 113° 8' and 66° 52'. 



Lustre of the lateral faces of the prism, vitreous ; that of 

 the base, pearly. Varies from translucent to transparent. 

 Hardness 2 ; may be scratched by the nail. 



Specific gravity of a transparent white crystal from Oxford, 

 as determined by Hisinger, 2.310; from 2.3121 to 2.3257 

 {Beudant). 



-S The compact varieties of this mineral are often known by 



the name of Alabaster. 

 Composition. This mineral is composed, in 100 parts, of sulphuric acid, 46.00; lime, 

 33.00; water, 21.00. 



» Report of a Re-examination of the Economical Geology of Massachusetts, 1839. 



