0B^ Dr Reichenbach on Petroleum or Mmeral Oil 



passes through unweakened, wiiile the other disappears, or ap- 

 pears only as a red light. If, on 'the other hand, we take for 

 the uniting substance, alcohol, or white of eggs, the extra- 

 ordinary ray, where refraction is 1,328, passes through, and the 

 ordinary ray is lost. This plan is decidedly inferior to that of 

 Mr Nicol, as the images it affords are dull and coloured. 



ON PETROLEUM OR MINERAL OIL. By Dr ReICHENBACH. 



Although petroleuifi has been found in nearly all the coun- 

 tries of the globe, from the finest Persian naphtha, through all 

 the gradations of the white, reddish-brown, and black mineral 

 oil, to the impure earthy pitch, yet we have remained quite in 

 darkness as to its origin, notwithstanding the numerous oppor- 

 tunities presented for the investigation. Among the many con- 

 jectures proposed by various naturalists, that theory has met 

 with most support which ascribes the formation of petroleum to 

 subterranean processes of charring and combustion which had 

 previously been in operation in coal deposits. This view how- 

 ever is entirely hypothetical, for the formation of petroleum has 

 never been observed as a consequence of combustion in coal- 

 mines, nor has any one succeeded in obtaining it by the carbo- 

 nisation of coal either in open or in close vessels. The con- 

 sideration that this subject stands in the closest relation to the 

 products of the dry distillation of organic bodies, has induced 

 me to make experiments upon it, and the following notice will 

 shew how far I have succeeded in removing the veil which has 

 hitherto obscured the question. 



In a large iron retort, I placed 50 kilograms of coarsely 

 divided coal, and mixed it with a considerable quantity of water. 

 The coal was from Oslawann, two miles west from Briinn, from 

 the principal coal formation, and is one in which species of Cala- 

 mites, Sphenopteris, and Odentoperis are found in abundance. 

 I now carried on distillation so long as water passed over, but 

 not longer, so that no carbonisation could take place. It was 

 merely with the intention of avoiding this with certaint}'; and to 

 prevent all deception, that water was employed. As soon as 

 the products of distillation began to pass over, I perceived a 

 coating of oil on the water, and upon opening the apparatus the 



