Of WHINSfONE and LAVA. 87 



in the manner already defcribed, and heated red hot. It a- 

 mounted to 9 parts for every 100 parts of the bafalt employ- 

 ed. 



In this experiment, the fulphuric acid was firft united to a part 

 of the lime, of the argil, and of the iron, contained in the (tone ; 

 and afterwards, when the mafs was expofed to a red heat, the 

 acid was driven off party or wholly from thefe, and applied in 

 red hot vapours to every part of the powder ; by which its ac- 

 tion appears to have been rendered much more powerful, as 9 

 per cent, of fulphate of foda was produced : and by the fame 

 procefs, fo iimple and eafy to execute, I got from the reft of 

 the fubftances, to be mentioned in this paper, from 8 to 1 1 per 

 cent, of fulphate of foda, although, when the were merely boil- 

 ed in the acid, the quantity of this fait never exceeded 5 or 6 

 per cent. 



As the proportion of acid and alkali in neutral falts has not 

 been hitherto determined with certainty, the quantity of foda 

 in thefe whins cannot be exactly known. But it is probable 

 that 9 parts of fulphate of foda, dried by a red heat, do not 

 contain lefs than 34- or 4 parts of pure alkali*; which muft 

 therefore be conlidered as the weight in 100 parts of the bafalt 

 of Staffa : and as 37 or 4 parts of foda, when added to the fum 

 of the earths and iron, amount nearly to the 100 parts of the 

 ftone employed in the analyfis, this calculation may be reckoned 

 very near the truth. For the fame reafons I think it likely, that 

 the greater part, or the whole of the foda, was obtained from the 

 bafalt by the procefs which has been laft defcribed. 



It is well known among the friends of the late Dr Hutton^ 

 that he made fome experiments on zeolite ; by which he con- 

 cluded, that foda entered into the compoution of that fub- 



ftance* 



* This is nearly tbe proportion given by Mr Kir-wan. 



