1818.] Siliciferous Subsulphate of Alumine. 433 



places where it is streaked with peroxide of iron. It has the 

 consistency of hogs-lard, for which indeed the miners mistook 

 it, is perfectly smooth to the touch, and is, for the most part, 

 moderately translucent, except in small patches where it is 

 opaque and granular. Its taste is sub-acid, and it distinctly 

 reddens paper stained with litmus. When exposed to the air it 

 dries, and in drying splits into lengthened masses like starch, 

 some of which are efflorescent on the surface, while others 

 resemble in translucency the finest pieces of gum arabic. By a 

 temperature of 160° Fahrenheit long continued, 100 parts are 

 reduced to 13. These, by ignition, are further reduced to eight, 

 and the fragments acquire hardness enough to scratch glass: 

 The loss of weight, however, is not constant in different speci- 

 mens, which evidently vary in their degree of moisture. 



Chemical Properties. 



1. The substance in its native state (or hydrate as it maybe 

 called) is miscible with water by trituration ; and when a large 

 quantity of water is added, it subsides slowly. Only a small 

 part of it is soluble ; for 100 grains digested with four fluid 

 ounces of water, which was afterwards evaporated to half an 

 ounce, gave a solution of the specific gravity 1006. It had the 

 chemical properties of a weak solution of sulphate of alumine, 

 and was very slightly contaminated with iron. 



2. The hydrate dissolves readily, and with a scarcely percep- 

 tible residuum, in diluted sulphuric, nitric, and muriatic acids. 

 With the first, it gives a solution, which does not yield crystals 

 on evaporation, but a spongy, opaque mass, unless the addition 

 be previously made of sulphate of potash, when it affords crystals 

 of alum. The spongy mass which has been alluded to, if dried 

 at a long continued heat of 160°, does not entirely re-dissolve 

 in water, but a light flocculent substance floats in the liquid. 

 This, when collected from a solution of 100 grains of the 

 hydrate, weighed three grains, after being exposed to a low red 

 heat. Suspecting, from its appearance when treated under the 

 blow-pipe with fluxes, that it still contained alumine, I boiled it 

 with sulphuric acid and a little sulphate of potash ; washed, 

 dried, and again ignited it, when it was reduced to 2*4 grains. 

 These had all the properties of silica. The fact furnishes an 

 additional proof that silica, though separately insoluble in certain 

 acids, may accompany alumine into solution.* It shows also 

 that silica, precipitated from a solution of alumine, carries down 

 with it a little of the latter earth. The sulphuric solution of 

 100 gr. freed from silica, gave, by decomposition with carbonate 

 of ammonia, 6*5 gr. of ignited alumine. 



3. One hundred grains of the hydrate dissolved in dilute 



* Sre Slrnmryrr, Ann. dc Chiui. lxxxi. 239; and Marcet, Gcoloz. Trins. i. 245 



Vol. XI. N° VI. 2 E 



