78 



distillation at low temperatures gave., on heating to a high tem- 

 perature, other volatile products, some rich in sulphur. 



In modern well-established works the oil shale is heated in 

 retorts to about temperatures between 900° and 1300° Fahr. The 

 result is the liberation of (i) gas, which is stored and used for 

 heating and illuminating purposes on the works ; (ii) crude oil, 

 which is pumped into tanks and afterwards refined ; (iii) naphtha 

 or petrol ; (iv) ammonia water, which is distilled and treated for 

 the manufacture of sulphate of ammonia ; and (v) spent shale, con- 

 sisting essentially of silicate of alumina with 2 to 3 per cent, of 

 fixed carbon. The crude oil as it comes from the retorts is of a 

 dark colour with a specific gravity of between .90 and .95. 

 Refining, or, as it is technically termed, " fractionising," is really 

 subjecting the crude oil to the application of heat at varying tem- 

 peratures in closed retorts of special construction, by which treat- 

 ment the portions of oil vaporising at different temperatures are 

 driven off and recovered as separate and distinct units. 



The first distillate is Petrol or Benzene. As the heat is 

 increased and the necessary temperatures are reached to volatilise 

 the respective grades of oil it is desired to produce, there come 

 over in rotation (i) illuminating or lamp oil, (ii) gas or solar oil, 

 (iii) lubricating oil, (iv) fuel oil, and (v) paraffin wax, leaving (vi) 

 still coke or a residue. These oils, as produced, are subjected to 

 further treatment with sulphuric acid, caustic soda, and other 

 re-agents for purification, according to the nature of the deleterious 

 impurity. With respect to sulphur it is generally recognised that 

 the higher grade oils should not contain more than 0.6 per cent 

 of sulphur, and lubricating and fuel oils not more than 0.76 per 

 cent. In addition to distillation and "fractionating," another 

 process, known as " cracking," is also employed. This practi- 

 cally means the redistilling of the oils at temperatures higher than 

 the normal boiling points of the intermediate constituents, and so 

 breaking up the molecules of the constituent hydrocarbons into 

 lighter and more valuable fractions. In this way the yield of both 

 petrol and burning oil from the crude petroleum is greatly 

 increased. 



Economic Importance of Mineral Oils. 



The development that has taken place in the petroleum in- 

 dustry since it was first inaugurated on a large commercial scale 

 by Young in 1849 has been little short of marvellous. It still con- 

 tinues, and betokens the possibility, within a very short period, 

 of the existence and world status of a Power depending largely 

 upon its uncontrolled supply of hydrocarbon products. At first 

 sight it is scarcely conceivable that so much of prime importance 

 to the industry of a State should depend upon the supply of petrol, 

 paraffin oil, lubricants, etc. Yet so it is; and the British Empire, 

 not containing much oil-bearing deposits within its borders, is 



