4o8 AnulyfiS of Whinjlont and Lava. 



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, and loft exaflly the fame weight as in a low red heat. At 160 the effefts 

 were in every refpeft the fame ; the lofs not being greater in that intenfe fire. The fmall 

 crucibles, in which the pyrometers had been placed, did not in thefe experiments lofe the 

 fmalleft weight. 



The volatile matter thus driven off by heat is partly water, as the following experiment 

 {hows : 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 pneumatic 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 pafTed over \ but I could not afcertain with precifion either its 

 quantity or its nature, as it was mixed with the air of the receiver. I have not made far- 

 ther 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 thirty 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 fB'&rynefs, left only fome thin ftreaks 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, 

 were mixed, in a fmall retort, with about 1200 grains of muriatic acid; and a receiver 

 being adapted, the mixture was gradually heated till it boiled. It was at firftof a brownifh- 

 yellow colour, but afterwards became brownilh. Part of the powder was diflblved. To 

 diftill off the uncombined acid, the heat was continued till the mixture began to grow 

 thick. It was then diluted with boiling diftilled water, and poured on a filter; and the 

 undiffolved part, after proper edulcoration, being dried and heated red hot a few minutes 

 weighed 67 grai ns, and was greyifti-white. 



2. The filtered folution was of' a faint yeliowifli-brown colour. Being faturated with 

 cauftic ammonia, a bulky precipitate was thrown down, which was carefully feparated by 

 filtration. It had at firft a dirty greenifti-colour, which was afterwards changed to brown 

 by the aftion of the air. 



♦ The fufibility of this, and tlie other fubftances to be afterwards mentioned, I examined with Sir James 

 Hall. For tliis purpofe, a fmall piece of each was placed, with a pyrometer as near to it as poffible, in an 

 open muffle previoufly lieated to rednefs. It could thus be feen peifeftly during the operation, and tlie 

 fire being raifed, as foon as it was found to be Ibft, when preffed (lightly by an iron rod, the degree of 

 heat was afcertained by meafuring the pyrometer. 



f The mortar I ufed was not fcratched by any of the whins or lavas mentioned in this paper. 



4 3- The 



