J 2 Experiments on Whinjlone and Lava. 



cavities produced by air bubbles,, the internal furface of which was lined with diftinft 



* 



cryftal; 



Having fliewn this refult to feveral of my friends, Dr. Hope regretted that the fubftance, 

 previoudy to its artificial cryftallization, had not been reduced to the ftate of folld glafs ; 

 fince the adverfaries of the fyftem might alledge, that, during the aftion of heat, the ori- 

 ginal cryflallized texture of the (lone had never been completely deflroyed. Being con- 

 vinced of the propriety of this obfervation, I determined, in future, to reduce the flone 

 firft to glafs, and to perform the cryftallization after a fecond fufion. 



For this purpofe, with the affiftance of Dr. Kennedy, to whofe co-operation I am 

 greatly indebted for the fuccefs of all the following experiments, I reduced a quantity of 

 the fame whinftone to moft perfed black glafs. A crucible, filled with fragments of this 

 glafs, being then expofed to a heat, which, from previous trials, was judged to be more 

 than fufficient to reduce its contents to fufion, the fire was very gradually lowered till all was 

 cold. I thus expedled to obtain a refult fimilar to that laft mentioned, but found, to my 

 great furprifc, that the fragments had never been in complete fufion, fince they ftill, in a 

 great meafure, retained their original ftiape. This extraordinary faft, which afterwards 

 led to the difcovery of fome curious properties of whinftone, will be fully accounted for ia 

 a fubfequent part of the paper. 



Another portion of the fame glafs being perfeftly melted by a very ftrong heat, the 

 temperature was reduced to about 28 of Wedgwood, and was maintained at that pitch 

 during fix hours. The refult was a perfectly folid mafs, cryftallized to a certain depth 

 from the outfide, though ftill vitreous in the heart. In another experiment, performed 

 like the laft in all refpe£ls, except that the heat was maintained at 28 during twelve hoursi, 

 I obtained a mafs entirely cryftalline and ftony throughout, with facettes appearing in the 

 folid parts, and fmall cryftals (hooting into fome of the cavities. 



Soon after I had communicated thefe refults to Dr. Hope, he performed, with complete 

 fuccefs, an experiment fimilar to the firft, in which I had obtained a cryftallized fubftance, 

 by the gradual cooling of the melted ftone. The fame was likewife, • foon afterwards, 

 performed by Mr. Bofwell of Auchinleck. 



My experiments, already defcribed, were confined to one fpecics of whinftone ; but 

 have fince been extended to fix other varieties. They were all firft reduced to glafs by the 

 application of a ftrong heat, and fubfequent rapid cooling. After a fecond fufion they 



By this reduflion, as a portion of its iron was withdrawn from the mafs, and as the relative proportion of 

 the component elements was thus varied, the nature of the original fubftance could not fail to be changed. 

 I determined, on this account, to lay afide black lead crucibles in future. The propriety of this has fince 

 been fully proved ; for the firft refult is found to differ efFentially from thofe obtained in all my fubfequent 

 experiments, which were performed with Heffian crucibles, or with otheri, which, like them, contain no 

 fenfible quantity of carbonic matter. 

 * I fhowed this refult at a meeting of the Society on 5th of February.. 



were 



