88 On the Photo gen Oils. 



had attracted the remark of a party of boys, "who were making 

 a last desperate foray upon the crabs — with indifferent suc- 

 cess indeed, for if Cancer could but make good his refusal to 

 be taken at sight, the rapid strides of the tide quickly beat off 

 his assailants, and left him in quiet possession of -the field. 

 A small eel, under the title of a " Skittle-jack," was brought 

 to me, as likely to be of interest to a man that seemed to be 

 very easily amused ; and an animated discussion as to whether 

 all the smaller mollusca did not ultimately grow up into 

 " covings," i.e., mussels for bait, was stifled by the biggest 

 lad declaring that crabs were the best, but shells he thought 

 " nowt aboot." 



ON THE PHOTOGEN OILS. 



BY J. W. M'GAULEY. 



The Natural Products. — The fluid bitumens obtained native, 

 and those derived from coal and shale, are believed to be iden- 

 tical, or at least so closely allied as to yield products very nearly 

 resembling each other. Native bitumens are generally con- 

 sidered to be of vegetable origin ; a few geologists, however, 

 believe they may be due to the slow subterranean alteration of 

 fish, deposited at some geological period. They certainly differ 

 from coal, in never exhibiting any organic tissue or structure 

 under the microscope, and in consisting of viscous matters, 

 which ordinarily melt at or below the temperature of boiling 

 water. The solid bitumens are termed Asphaltes. The semi- 

 iuid bitumens consist of Asphaltine, which is solid and fixed, 

 and Petroline, which is fluid or volatile ; and their constituents 

 may be separated, by exposing them to the temperature of 

 boiling water, in a close vessel. They are found as wells or 

 springs of viscous fluid, which has been forced up through the 

 deposits above them, and which, in some instances, hardens at 

 the surface and edges. 



The rock oils, or native naphthas, are obtained in many parts 

 of the world, and hence I heir various names — Persian naphtha,, 

 Rangoon tar, etc. ; the old generic term Petroleum being, as is 

 perceived (prtri-olrnm), a more Latin form of the English 

 appellative. They are probably all alike in constitution, and 

 when properly rectified none of them contains any oxygen, or 

 has any tendency to unite with it — an important quality, as 

 they are often used for the lubrication of machinery; but, 

 though consisting only of carbon and hydrogen, they are very 

 complicated compounds. They are found at Amiano in Italy, 

 Clermont in France, Neufchatel in Switzerland, and many other 



