7S CHEMICAL AN J ITS IS 



been placed, did not in thefe experiments lofe the fmalletl 

 weight. 



The volatile matter thus driven off by heat is partly water, 

 as the following experiment mows : I put half a pound Troy of 

 the bafalt in fragments, into a fmall Wedgwood retort, and 

 luted to it a receiver, into an aperture of which was fitted one 

 end of a glafs tube, the other end being adapted to a pneuma- 

 tic apparatus. The retort was then heated flowly to rednefs, 

 and kept moderately red hot for two hours. In the receiver 

 fome water was condenfed. Some gas alfo palled over; but I 

 could not afcertain with precifion either its quantity or its na- 

 ture, as it was mixed with the air of the receiver. I have not 

 made farther experiments on the volatile matter contained in 

 whins ; but it deferves to be examined with attention. 



This bafalt being expofed to heat in a muffle, was found to 

 foften at 38 of Wedgwood *« 



Some of it being reduced to fine powder, was boiled in thir- 

 ty times its weight of water for half an hour. After filtration 

 the water was examined with different chemical tefts, but gave 

 no precipitate with any, except a flight cloud with nitrate of 

 filver ; and a portion being evaporated to drynefs, left only 

 fome thin flreaks on the bottom of the glafs. 



Having premifed thefe particulars, I proceed to defcribe the 

 analyfis. 



1. One hundred grains of the bafalt, reduced to fine powder 

 in a Wedgwood mortar f, were mixed, in a fmall retort, with 



about 



* The fufibility of this, and the other fubftances to be afterwards mentioned, 

 I examined with Sir James Hall. For this purpofe, a fmall piece of each was 

 placed, with a pyrometer as near to it as poffible, in an open muffle previoufly heat- 

 ed to rednefs. It could thus be feen perfectly during the operation, and the fire be- 

 ing raifed, as foon as it was found to be foft, when prefled {lightly by an iron rod, 

 the degree of heat was afcertained by raeafuring the pyrometer. 



+ The mortar I ufed was not Scratched by any of the whins or lavas mentioned 

 in this paper. 



