56 Original Articles. [Jan., 



Professor Evans does not think that in any case the oil is raised to 

 the surface by the direct pressure of water, the heads of which are 

 higher than the issue, as Artesian wells are said to be produced-, but 

 inclines to the belief that the flow is due exclusively to the pressure of 

 gas accumulations. In support of this, he shows that gas always 

 escapes from spouting wells, and that a current of water would be sure 

 to float away the oil, the springs in such vicinities being tainted in 

 this way. The finding of oil in association with water is not, how- 

 ever, a reliable sign of the presence of oil below, because it may have 

 come many miles ; but the presence of gas, which is much less likely 

 to be transported downwards and to a distance, is regarded as a valu- 

 able indication. 



Petroleum of different localities varies greatly in character. Ordi- 

 narily of a greenish colour, it may present greater or less degrees of 

 opacity ; it is sometimes reddish ; as it occurs in natxne it is of no 

 fixed composition, but consists of various hydrocarbons holding in 

 solution paraffme, and more or less bitumen or asphaltum. Tho 

 appearance of the oil turns on the proportion of these solid ingredients. 

 As the amount of asphaltum increases, the oil becomes more and more 

 like tar, eventually passing into a substance possessing so little fluid 

 matter as to be solid at ordinary temperatures. This is its condition 

 as found in Tar Lake, in the island of Trinidad, and it is then suit- 

 able for making pavements or hydraulic works, or for replacing pitch. 

 The refined oil has a characteristic smell, which is not entirely 

 removed by the usual process of purification, though, by standing 

 several days over an alkaline solution and freely exposed to the air, 

 it may be caused to disappear. The best American oils are those 

 from Oil Creek, which mark 46 :) on B^aume's hydrometer; those from 

 Mecca have a density of 26° or 27°, and will not flow when cold. A 

 new method has been recently introduced for testing the illuminating 

 oil, instead of depending on the hydrometer alone ; it consists in 

 observing the temperature to which the fluid must be raised before it 

 can be set on fire by a flame. That is preferred which ignites at from 

 100° to 120° Fahr. The proportion of light oils suitable for burning 

 in the best Petroleum is sometimes ninety per cent. ; other specimens 

 will not yield thirty per cent. The heavy oils parted from these 

 during distillation are only useful for lubricating, and even then 

 require the admixture of animal oil to give body. The paraffme 

 which remains behind with the heavy oils is separated by the aid of 

 cooling mixtures and pressure, and exists in very different proportions 

 in different samples. The average yield is said to be about one pound 

 from four gallons of Petroleum. 



The processes for rectification of Petroleum do not differ greatly from 

 those formerly used for crude coal oil, produced from the distillation of 

 bituminous shales, &c. This latter operation is an old one, having been 

 patented in England in 1694 by Martin Eele, Thomas Hancock, and 

 William Portlock. The discovery does not seem to have been attended 

 by any practical consequences until the present century, when the whole 

 subject of the effect of distillation at high and low temperatures, not 

 only of these but of animal and vegetable substances, was thoroughly 



