EFFECTS OF HEAT. -101 



^luti'nated, but aftually fufed; the fubftance Gnking upon itfelf 

 with a round and glofly fiirface, and exhibiting every proof of 

 a vifcid fluidity, fiinilar to that of melting fealing wax. Iti 

 general the fufion has been accompanied with a flight ebulli- 

 tion, which has fometime.s changed the mafs to a kind of froth, 

 and fometimes has merely produced fome fcatiered air bubbles. 

 The wiiole externally and in its fradure fliines much; thi« 

 fliine, arifing in fome cafes from numberlefs facettes of cryftal- ' 

 Jization, and in others from a fraooth and continued glofs, like 

 that of glafs. In many fpecimens the cryftallization of newly Sparry cryftala 

 formed fpar is diftinc^ly vifible; the cryftalline mafs confiding bonat^, u e ca • 

 of parallel plates, which reflect together with one glofs. Some 

 of thefe are difcernible by the naked eye, though in general to 

 fee them well we require the help of a lens. As foon as the 

 carbonate becomes foft, it begins to act powerfully on the tube 

 of porcelain (generally formed of pure Cornifh clay) in which 

 it rs confined; the compound fliewing itfelf to be much more AiVionofthc 

 fufible than the pure carbonate. It penetrates the minuteft day veflcl^" 

 crevices, and fpreads along the cup to a confiderable diftance 

 from the point of contadt between the carbonate and the tube; 

 its termination being marked by a black line, the caufe of 

 which I have not difcovered. Previous to this ftage of fufion 

 no acljon whatever feems to take place between the carbonate 

 and the porcelain, the former receiving from the latter an ac- 

 curate imprelTion of its fliape, acquired doubtlefs when the 

 powder was rammed into the tube. In this cafe the carbonate 

 remains quite loofe, and is often heard to rattle before the vef- 

 fel is opened. Where pounded filex has been rammed into Union of the 

 the tube in contadt with the carbonate, an union has fometimes ^,1^3^^ 

 taken place, producing a fubflance having fomewhat the ap- 

 pearance pf chalcedony, bijt which thews evident proof of 

 fufion, it having flowed fo as to form little flaladliles and tla- 

 lagmites. This fubftance effervefces feebly in acid, in fome 

 cafes it leaves a femi-tranfparent cloud of undilfolved matter, 

 in others diflblves entirely the folution, yielding a jelly when 

 evaporated to a certain pitch. This affords proof of a real 

 ijnion between the carbonate and the filex. 



in all the experiments alluded to in this paper, the vefllsis When the vef- 

 ,- . • I , r r L . • I fels have failed, 



pave been expoled to a violent expanlive torce, by which a- the carbonate has 



great number of them have been deftroyed, and the experi- fl»ewn different 



ments have often been loft or refalts obtained only of partial j^^^^^J aaid. 



3 f^^ccef^ , 



