220 ANNUAL OF SCIENTIFIC DISCOVERY. 



have been carried on at the Clifton quarry at Windsor about 40 

 years. The principal rock is gypsum, the anhydrite, a hard plas- 

 ter being found in lenticular masses from 2 to 10 feet thick in the 

 centre, and sometimes 50 feet long, imbedded in the soft plaster. 



Gypsum is exported as blue and white gypsum ; the former is the 

 kind chiefly used for agricultural purposes, and, before the recent 

 civil war in America, was being thought of as a manure for cot- 

 ton. The white gypsum is burned or boiled, by which the water 

 is expelled, and plaster is made by the addition of water. The 

 composition of pure gypsum was stated to be : 



Lime 32.55 



Sulph. acid 46.51 



Water . 20.94 



100.00 



A compact opaque white gypsum, called (locally) alabaster, 

 occurs in Antigonish, and has lately been found about 3 miles 

 from Windsor. Selenite, which is the finest kind of gypsum, is 

 abundant in. the quarries at Windsor. Other varieties differ in 

 composition from the admixture of oxide of iron, and carbonate 

 of lime and magnesia. Analyses were given of plaster exposed 

 to the weather, which did not vary from that of pure gypsum, of 

 black gypsum, and of hard gypsum (not anhydrite). The compo- 

 sition of anhydrite was stated to be : 



Lime 41.18 



Sulph. acid 58.82 



100,00 



True anhydrite can give no water. It makes a very good sub- 

 stitute for marble in in-door work ; does not admit of being made 

 into plaster by burning, but is equally good if not more valuable 

 than gypsum for agricultural purposes. 



No deposit of rock salt of any importance has been found with 

 ,the gypsum ; but the brines of the gypsiferous districts have fur- 

 nished excellent salt at River Philip and Springhill, Cumberland. 



PEKCHLOKIDE OF LEAD. 



M. Nickles, Professor of Chemistry at Nancy, recently an- 

 nounced to the Academy of Sciences that he had succeeded in 

 obtaining perchloride of lead, derived from the only compound of 

 lead and chlorine, and which now must be called protochloride. 

 The latter is obtained directly by subjecting lead to the influence 

 of chloriwe by the application of heat, or else by treating litharge 

 with hydrochloric acid. It crystallizes in needles, is volatile, and 

 cannot be decomposed by heat. M. Nickles has obtained the new 

 compound by exposing the protochloride to the action of a current 

 of chlorine in a solution of chlorid*' of lime. The perchloride thus 

 obtained is a yellow liquid emitting a strong smell of chlorine, 

 and is a powerful agent for communicating that element to other 

 substances. It will dissolve gold, and produces with aniline and 

 the analogous coniDounds those beautiful colors for which those 



