314 Proceedings of the Royal Physical Society. 



is used. The products of this distillation are oil, ammonia 

 water, and an uncondensable gas, which latter is brought back 

 to heat the next charge of shale. The ammonia water is 

 separated from the oil, and by one or another means the 

 ammonia in it is converted into sulphate of ammonia. 



The oil more particularly concerns us. From the receiving 

 tank of the retorts it is pumped into a charging tank, and 

 from this charging tank it is run into stills, which are 

 generally known as the " crudes!' 



In this distillation, as in all distillations throughout the 

 process, varying percentages of steam are used. The distillate 

 is only slightly fractionated, naphtha being separated. The 

 oil is now known as " once run oil!' 



From the receiving tank of the crude stills the oil is 

 pumped into a washer; a washer being a suitable vessel, 

 able to contain from 500 to 7000 gallons, the contents of 

 which may be stirred either by air or by some mechanical 

 means. On the oil in the washer sulphuric acid is run, and 

 the contents agitated as long as is necessary to saturate the 

 acid with tar. This tar is run off, and a second quantity of 

 acid is added. In like manner this also is agitated, allowed 

 to settle, and the tar run off. This process is continued until 

 all the tar, which it is advisable to separate at this stage, is 

 carried off. At the end of the last agitation the oil is allowed 

 to settle for about three hours, in order to allow the tar more 

 completely to separate. After settling for this length of 

 time, the oil is run into what is known as the soda washer, 

 where it is treated with a strong solution of caustic soda, 

 in order to neutralise any acid which may be left in the 

 oil, and to prepare the oil for another distillation. 



From the soda washer the oil is pumped, blown by means 

 of air pressure, or run into the second stage boilers or stills ; 

 from these stills it is fractionated into a light portion, specific 

 gravity about decimal 828, which contains little or no solid 

 paraftine, and a heavier portion, specific gravity about decimal 

 877, which, at 60° Fahrenheit, is solid with parafiine. 



The light portion is taken and treated with acid and soda, as 

 before, and is then again distilled. The distillate is fraction- 

 ated into decimal 84, decimal 85 oil, and oil at about decimal 



