414 Method of Jixing Particles on the Sappare, [Dec. 



certainly admits of the fusion being attributed to an accidental 

 cause. 



But I have found with much surprise that flint can be melted 

 without difficulty ; and even of a considerable bulk. Where the 

 heat is most intense, a degree of frothing takes place ; where it 

 is less, there is a swelling of parts of the surface. The effects 

 were the same with French and English flint, with black and 

 with horn-coloured. Does flint, like pitchstone, contain bitu- 

 men, which, at a certain heat, tends to tumefy it ? This might 

 explain the smell from its coUision, and the oil which Neumann 

 obtained by its distillation, and to which no credit has been ever 

 given. No doubt can, 1 conceive, be entertained of flint being 

 a volcanic production. On this point I may speak again at a 

 future opportunity. 



In using mere water, diamond, anthracite, plumbago, were 

 particularly difficult of trial, as any adhesion they had contracted 

 with the sappare was quickly destroyed by the combustion of 

 their surface, while, as the intention in their case is not to sub- 

 ject to great heat, they may be so secured in the clay as at 

 least very much to retard their escape. Here acting on very 

 minute particles is essential, as when large pieces are employed, 

 the effect is too slow to be perceptible. 



A pleasing way of demonstrating the combustion of plum- 

 bago, and of even exhibiting the iron in it, is to rub a little from 

 the wetted point of a pencil on one of the clay plates mentioned 

 in a former paper.* 



In trying diamond it was imagined that its glow continued an 

 unusual time after removal from the fire. The present method 

 afforded the means of making a comparison. A fragment of 

 diamond, and another of quartz, chosen purposely of rather a 

 larger size, were fixed neaj* each other in the clay ; and it was 

 observed that the diamond was most luminous while under the 

 action of the flame, and longer so after removal from it. Its 

 being a very slow conductor of heat may occasion in part the 

 latter quality. 



In the same way the unequal fusibihty of two substances may 

 probably, on some occasions, be ascertained ; and serve, from 

 deficiency of a better, as a means of distinction between them. 

 I am, Sir, yours, &c. . J. Smithson. 



* Annals for May. 



