602 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



are identical in atomical construction, and possessing the same physical 

 properties. Common petroleum of a low specific gravity usually contains a 

 portion of marsh gas, olein, stearine and resin, with a brown substance, 

 in solution. It differs greatly in color and consistency; some are dark and 

 viscid, others are transparent, very fluid and volatile, others are dark 

 brown, thick, unctions looking fluids, resembling Orleans molases, and pos- 

 sessed of high lubricating qualities. More generally it has an .oily con- 

 sistence, a brown or greenish color, and a strong penetrating characteris- 

 tic odor. It may be regarded as a compound of several of a large group 

 of bituminous substances, which differ much in physical character, while 

 they present a striking similarity in chemical composition. The more limpid 

 varieties mix with alcohol, ether and all the oils, both essential and unc- 

 tious. They dissolve iodine, phosphorus, sulphur, most of the resins, wax, 

 spermaceti, and soften caoutchouc, forming a gelatinous varnish with it. 

 These are the leading physical characteristics of petroleum in its crude 

 state. If we examine the crude coal oils, we find but a few of its charac- 

 teristics in them, but that few are peculiar to them all. In refining petro- 

 leum, we find that it differs from coal oils, in requiring a greater heat for 

 their distillation; and what is most singular in the matter is, that the boil- 

 ing point of petroleum is generally considerably lower than coal oils, the 

 petroleums boiling at 160° to 201'' and upwards, (some even lower,) but 

 the lowest boiling point I have found in coal oils has been 216° Fah. As 

 I remarked the other evening, petroleum yields a variety of oils of different 

 specific gravity, according to the temperatures to which it may be subjected 

 during distillation. 



This is a point of the most vital importance to the manufacturer, as an 

 increase of the degree of heat employed will change the properties of his 

 products, by increasing the proportions of the carbons, so much so as to 

 render it worthless for the purpose of illumination; while a temperature 

 too low would give results, equally disappointing. Each of the oils com- 

 posing the aggregate collection has a different number of the equivalents 

 of C. and H., with which the boiling points doubtless agree, but the exact 

 rate at which the boiling point does increase according to the proportions 

 of C. and H., present in the several oils, has not yet been determined, 

 although experiment has demonstrated that there does exist more than 

 one or two series of boiling points. In the fatty acids, alcohols, and other 

 bodies containing oxygen, the boiling points are uniformly about 34'^ Fah. 

 for every H^ Cj. But the hydrocarbon series seems to vary much in their 

 boiling points. I have found the boiling points of some of the more vola- 

 tile productions to be only 18° apart, while others less volatile were 25°; 

 some were 34°, and above this point they are so irregular that I presume 

 there must be a number of series yet unexamined, as some of them range 

 from 20° to 40° and upwards above the last regular point 34°. It is a 

 well known fact that the greater the quantity of C. in proportion to the H, 

 any of these oils contains the greater is its specific gravity, the higher its boil- 

 ing point, density of vapor, and tendency to smoke when employed for illu- 

 minating purposes. And that some of these oils, a much larger proportion 

 than others there cannot be any doubt. A short time ago I had occasion 

 to make some inquiry in regard to an oil that was weighed to go to a port 



