35^. Experiments on Charcoal expofed to 



and habits, to form a fort of afibciation. Does the pilot-fliV 

 feed on the dung of the fhark ? as C. Bofc thinks ; and has it 

 impofed on itfelf the painful duties of domefticity to iind pro- 

 tection and fafety in the neighbourhood of io voracious an 

 animal ? 



'- 

 LIX. Experiments on Charcoal evpnfed to high Degrees of 



Hctit in dole VtffUti By David M us he t, Ejq. of the 



Ca Icier Iron l\ o rk s t . 



i 



N a former communication I mowed that in Stourbridge 

 clay crucibles, made perfectly air-tight, a proportion of char- 

 coal ciifappeared much greater than : could poflibly combine 

 .with the iron in contact with it. Tins I attributed to caufefc 

 not yet afcertained, but worthy of ihveftig.ation. In mady 

 experiments with diamonds, particularly thofe ofD'Arcet and. 

 Macquer, it feemed that they dilappcared when inclofcd in 

 balls of porcelain, and where it was fuppofed no air was pre- 

 fent to promote combuftion. The fa6ts eftabliihed by thofe 

 eminent chemifts appeared thus at variance With thofe prin- 

 ciples by which the nature and properties of the diamond 

 and other combuftiblc fubflances were explained : nor have 

 1 yet learned if a fatisfa&ory explanation of them has been 

 given. 



Having prepared a parcel of fmall Stourbridge clay cruci- 

 bles nearly of the fame fize, I performed the following expe* 

 riments with different proportions of charcoal. 



Exp. I. In one of the crucibles was inclofcd five grains of 

 well dried charcoal : the crucible was yet moift. The mouth 

 was afterwards brought together and accurately (hut. When 

 well dried in a temperature from yo° to - 8o° of Fahrenheit, it 

 was placed in an annealing fire, and gradually heated till 

 of a bright red colour. It was then placed in the afiay 

 furnace, and a considerable degree of heat excited for the 

 fpace of 35 minutes. When withdrawn, and cold, it was 

 carcfullv examined, and found free from cracks. It was then 

 cautiouily broken, but exhibited no marks of charcoal : one 

 vitrid fpot only was obfervable upon the bottom, which I fup- 

 pofed to arife from the fufion-of the alkaline refiduum after 

 the deftruclion of the wood. 



Exp. II. In this the crucible contained ten grains of char- 

 coal. It was treated in the fame manner, only expofed to a. 

 more violent and continued heat. When cold, no cracks ap- 



* Communicated by the Author. 



peared, 



