CHEMICAL ANALTSIS, \3c. 77 



This bafalt, though reduced to fine powder, does not effer- 

 vefce with acids. The colour of the powder is greyifh, and 

 when wet greenifh. By being expofed to a low red heat, the 

 colour of the ftone is changed to brown. It is not attracted by 

 the magnet, either in its natural (late, or after being heated red 

 hot. 



. Its fpecific gravity, taken in diftilled water at the tempera- 

 ture of 60 ° of Fahrenheit, I found to be 2.872. 



Some fmall pieces being expofed to a low red heat for half 

 an hour, loft 5 per cent, in weight ; and when the ftone was re- 

 duced to powder, and heated red hot, *he lofs was the fame. 

 I alfo examined the effects of high heat on it, in the following 

 manner. Having made fome fmall crucibles of the porcelain 

 clay of Cornwall, which 1 ufed on account of its great purity 

 and infufibility, I baked them in pretty ftrong fires,, generally 

 above 100 of Wedgwood. As foon as they were cold, they 

 were each exactly weighed. A portion of the bafalt in frag- 

 ments, alfo weighed, being put into one of thefe fmall crucibles, 

 and a pyrometer into another of the fame fize, both were pla- 

 ced in a Heffian crucible. A fmall flat cover, alfo made of the 

 porcelain clay, was laid upon each; and then- a. lid was careful- 

 ly luted on the Heffian crucible with clay and fand. The ap- 

 paratus thus prepared was next fet into a furnace ; and the fire 

 being raifed gradually till it appeared to have attained the 

 pitch defired, it was kept as equal as poffible for about an. hour. 

 The fmalL crucible, and the -melted bafalt it. contained, being 

 weighed as foon as cold, it was eafy to determine how much 

 weight was loft. 



In this manner fome of the bafalt was- expofed to a heat of 

 72 of Wedgwood, at which it was vitrified, arid loft exactly 

 the fame weight as in a low red heat. At 1 60 the effects were 

 in every refpect the fame ; the lofs not being greater in that in- 

 tenfe fire. The fmall crucibles, in which the pyrometers had 



been 



