HOW — ON MINERALOGY OF NOVA SCOTIA. 3L 



cements are the names under which such plasters are known. 

 Stucco is coloured plaster mixed with size. (Miller's Chemis- 

 try, II. 801). If gypsum is mixed with a certain amount of 

 water and soaked in hot pitch it parts with water and takes 

 up pitch and forms a substance so hard and susceptible of polish 

 that it could be employed in making a variety of useful and 

 ornamental articles. Although the foregoing cements or most 

 of them are well known and much valued, it is said by a recent 

 observer that with one exception all admixtures impair the 

 hardness of plaster. The exception is iron filings. When these 

 are mixed with plaster they rapidly oxidise, and the coherent 

 mass of oxide of iron formed adds its own strength to that of the 

 plaster making a veiy firm material which has also the advan- 

 tage of uniting itself to surfaces of iron : it is supposed that the 

 filings should form about one-fifth of the whole weight to give 

 the best result. (Chem. News, No. 436, p. 182). It is obvious 

 that the manufacture of such substances as those mentioned 

 could be carried on here with the greatest possible advantage, 

 the quantity of gypsum being perfectly inexhaustible, and the 

 varieties numerous. 



Of these varieties the " isinglass" of the quarry men, selenite 

 of mineralogists is the purest. It is colourless and transparent 

 as flint-glass : it is abundant in some quarries. It has been 

 used in filling fire-proof safes. It cannot be used in place of mica, 

 with which it is often confounded under the incorrect name of" 

 tale, in stove doors, etc., as it becomes opaque in the heat. 

 Fibrous gypsum is found in veins, it affords very white plaster 

 as well as the foregoing. Compact white opaque gypsum, called 

 alabaster, is met with at Antigonish and also near Windsor at 

 Three Mile Plains and in Falmouth. That from Antigonish is- 

 suitable for carved work as was shewn by a small piece of work, 

 executed by the late C. Harding, Esq., of Windsor, sent to the 

 Dublin and Paris Exhibitions : some remarks on the durability 

 of this material and the propriety of having illustrations in 

 the Provincial Museum will be found in the last Part of these 

 Notes. (Trans. N. S. Inst., 1866). Between the other varie- 

 ties of gypsum there is a difference in composition fi'om the 

 admixture of variable amounts of oxide of iron, carbonates of 



