20 Chemical Examination of American Minerals' 



ring hot weather, I have frequently failed altogether in my 

 attempts to obtain it in regular crystals. Chemists will pro- 

 bably be surprised to learn that it exists native in South 

 America, and probably in considerable quantity. 



The specimens which I examined were sent to Dr. Hooker, 

 Professor of Botany in Glasgow, by Dr. Gillies, who is 

 settled at Mendoza, a city near the foot of the Andes, and 

 about 1200 miles to the west of Buenos Ayres. It was tick- 

 eted, Native alum from the province of St. Juan. 



The specimens are in irregular nodules, rather smaller than 

 a hen's egg. From the rocky fragments occasionally attach- 

 ed to them, they seem to have been imbedded in a slate, 

 which has a blackish-blue color, is very soft, and has a con- 

 siderable resemblance to the slate-clay, which usually accom- 

 panies coal beds in this country. But these stony fragments 

 are too minute to enable us to determine with certainty the 

 true position of the rock to which they belong. 



The alum is white, and composed of fibres adhering lon- 

 gitudinally, and having a certain breadth, but very thin. It 

 bears some resemblance to fibrous gypsum ; but is much 

 harder, not being scratched b}' the nail of the finger, though 

 very easily by the knife. It is sectile ; the outer fibres are 

 white and nearly opaque, obviously from the loss of a por- 

 tion of their water. But internally the fibres are transpa- 

 rent, and have a glassy, or rather a silky aspect, showing that 

 they contain a good deal of water of crystalization. The 

 specific gravity of the transparent fibres is 1'8S. 



It tastes exactly like common alum. But is much more 

 soluble in water. For at the temperature of 62°, 100 parts 

 of water dissolve 377-3 parts of it. And boiling water dis- 

 solves any quantity of it whatever. When exposed to heat, it 

 exhibits the same phenomena as common alum. When 53*25 

 grains of the transparent fibres were exposed to a red heat, 

 the loss of weight was 24*79 grains. But it will be seen im- 

 mediately, that the whole quantity of water in 53*25 grains 



