Analyfts ej IVhinftone and Lava> 407 



VI. 



A Chemical Analyjis of Three Species of Whinfione, and Two of Lava, By Robert 

 Kennedy, M. D. F. R. S. isf F. A. S. Edin. * 



O. 



'N the 5th of Auguft (1798) I announced to the Society that I had difcovered foda 

 in feveral varieties of the whinftone \ of Scotland, and alfo in lava from Mount ^tna ; 

 but did not defcribe the various experiments to which thefe fubftances had been fubjefted 

 in my examination of them. In the following paper, therefore, I have the honour of 

 laying an account of thefe experiments before the Society. 



ANALYSIS I. 

 Bafalt of Staffa. 



The fpecimen of this bafalt, fubmltted to the following analyfisj was given me by a 

 gentleman, who brought it himfelf from the celebrated bafaltic columns in StafFa. A 

 defcriptlon of its external mineralogical chara£ters may be found in Sir James Hall's paper, 

 (p. 8. and 56 of our prefent Volume) to which I beg leave to refer. 



This bafalt, though reduced to fine powder, does not efFervefce with acids. The co- 

 lour of the powder is greyifli, and when wet greenilh. By being e^gfed to a low red 

 heat, the colour of the ftone is changed to brown. It is not attra£led by the magnet, 

 either in its natural ftate, or after being heated red hot. 



Its fpecific gravity, taken in diftilled water at the temperature 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 reduced to powder, and heated red hot, the lofs was the 

 fame. I alfo examined the cffefts of high heat on it, in the following manner : having 

 made fome fmall crucibles of the porcelain clay of Cornwall, which I ufed on account of 

 its great purity and infufibijlty, I baked them in pretty ftrong fires, generally above 100 of 

 Wedgwood. As foon as they were cold, they were each exaftly weighed. A portion of 

 the bafalt in fragments, alfo weighed, being put into one of thefe fmall crucibles, and a 

 pyrometer Into another of the fame fize, both were placed in a Heflian crucible. A fmall 

 flat cover, alfo made of the porcelain clay, was laid upon each ; and then a lid was care- 

 fully luted on the Heffian crucible with clay and fand. The apparatus 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 poflible for about an hour. The fmall crucible,, 



• From the EdinbvH-gh Tranfaftions, 1799. 



■f- The name whmftone is uftd throughout this paper in a generic fenfe, comprelmiding bafalt, trap, 

 certain kinds of porphyry, wacken, and fonie other ftones of the argillaceous clafsi 



S and 



