24) Prof. Johnston on the Composition of certain Minerals. 



These are equivalent to 



Ist. 2nd. 



Carbon = 85-958 86-177 



Hydrogen = 12-3'1.2 12-423 



98-300 98-600 



It would appear that this variety also contains a small 

 quantity of oxygen. 



These analyses show us, 



1. That the elastic bitumens are very nearly akin to the 

 Hatchetine and Ozocerite, and are probably an equiatomic 

 carbohydrogen (CH) slightly altered. 



2. The first compared with the succeeding analyses shows 

 that in the soluble and more volatile of the two portions of 

 which these bitumens consist, the carbon and hydrogen are 

 more nearly in atomic proportion than in the elastic insoluble 

 portion, and render it probable that the soluble part is a 

 variety of Hatchetine or Ozocerite, of which originally the 

 entire mass consisted ; and therefore, 



3. That the change which the originally pure carbohydro- 

 gen has undergone, has either been the result of a decompo- 

 sition analogous to that which many of this group of carbo- 

 hydrogens are known to undergo, or of an oxidation to a 

 small extent, perhaps of both. If oxidized it may either be 

 so by the direct addition of oxygen to the unchanged com- 

 pound, or by the replacement of a portion of its hydrogen, 

 in which case the atomic ratio of the fundamental elements 

 must be altered. Were we certain that the second variety 

 analysed was wholly free from mixture, the ratio of its ele- 

 ments might be calculated and the true nature of the change 

 determined; while doubt remains in regard to its purity, 

 however, the result of such a calculation would be deserving 

 of little confidence. 



In regard to the origin of this substance, I am inclined to 

 attribute its presence in the mineral veins and fissures which 

 traverse the mountain limestone in Derbyshire, to sublimation 

 from beneath. The immense stratiform deposits of trap which 

 traverse that district, indicate a sufficient cause for such 

 sublimations. The contact of a fused lava with the organic 

 matters which abound in the strata of the carboniferous aera, 

 could not fail to cause the evolution of volatile substances, which 

 would condense when they reached a colder region. Bitu- 

 minous substances are found also in the carboniferous lime- 

 stone in Fifeshire, where trap rocks are known to penetrate or 

 disturb the strata; and it is not unlikely that in most cases 

 their appearance near the surface is due to a high temperature, 



