96 Mr. Smithson on a Native Compound of [Aug. 



novelty. Cherry coal yields almost pure carburetted hydrogen 

 gas. The goodness of coal gas depends very much upon the 

 rapidity with which the heat is applied. By long continued low 

 heats, I have never been able to obtain a gas that burned with 

 a strong light. I have tried what kind of gas could be obtained 

 by decomposing the coal tar ; but the result did not answer my 

 expectation. The gas obtained yielded too little light to make 

 it worth while to prosecute such experiments further. 



It is obvious, from the preceding experiments, that the four 

 kinds of coal found in the neighbourhood of Glasgow are com- 

 posed each of definite proportions of their constituents, and, 

 therefore, that they constitute four distinct species of coal, 

 which must be placed separately by mineralogists. I present 

 them with these results as a first approach to the arrangement of 

 coal. When similar experiments are sufficiently varied and 

 extended, we shall know whether all the varieties of coal 

 can be arranged under these four species, or whether there do 

 not still exist other species of coal not found in this neighbour- 

 hood. 



Article II. 



On a Native Compound of Sulphuret of Lead and Arsenic. 

 By James Smithson, Esq. F.R.S. 



Paris, May 19, 1S19. 



This mineral is found in Upper Valais, in Switzerland. It is 

 lodged in *a white, granose, compound carbonate of lime and 

 magnesia. It is accompanied in this rock by regular crystals of 

 yellow sulphuret of iron ; by red sulphuret of arsenic ; and by 

 some other substances. 



This compound sulphuret has a metallic aspect. It is of a 

 grey colour ; it is exceedingly brittle and soft ; its fracture in 

 some directions is perfectly vitreous ; but in at least one direc- 

 tion, it is evidently tabular ; but the size of the fragments I had, 

 not exceeding coarse sand, precluded research with respect to 

 crystalline construction. By trituration, this ore afforded a red 

 powder. 



At the blow-pipe, this ore melted instantly on the contact of 

 the point of the flame. It smoked considerably ; and a small 

 flame was visible on the surface of the melted button. On cool- 

 ing, this button forced out a quantity of fluid matter from its 

 interior. During the fusion, the bead occasionally swelled up, and 

 puffs of dense smoke issued from it ; due evidently to a volatile 

 matter, which the fire expelled from another less volatile. Finally, 

 abutton of amore fixed, less fusible, white metallic matter, exten- 

 sible under the hammer, was left, and which proved to be lead. 



