i6'2 ON THE ASSAY OF COAL FOR CRUDE OIL, ETC. 
is passed ; in sncli an atmosphere the heavy paraffin and other vapours rise 
and flow ofi* better than in a current of steam, A fifth of a litre of the once- 
run oil, or of the crude oil or petroleum, if not of very bad odour or colour, 
is now mixed with about ten cubic centimetres of strons^ sulphuric acid and 
agitated frequently during a period of from two to three hours. The mixture 
is set aside for the oil and acid to separate, the oil poured off from the thick, 
treacle-like deposit (“ foots ”), washed two or three times with water, and 
then shaken with about the same quantity of a strong solution of caustic soda 
(sp. gr. 1’3 or 1‘4) for an equal period. The soda solution having subsided, 
the oil is poured ofi’ and washed by agitation with vuter. If the oil is still 
of bad odour it is again treated with acid and soda as before, at a moderately 
warm temperature (30*^ to 35° C.) ; and sometimes a third treatment is neces¬ 
sary. Sometimes, also, the oil is best treated b}'' soda first and acid after¬ 
wards. It is now redistilled in the manner already described, three chief 
fractions being collected separately, the volume of each noted, and its specific 
gravity taken. The fraction of lowest boiling-point, the “ spirit,” may in this 
first fractionation have a specific gravity of 0‘750 ; the next, the burning-oil 
or “photogen,” of 0*850 ; the “lubricating oil” will be the fraction coming 
over at the highest temperatures. Each of these fractions may now be once 
redistilled: the spirit will yield some photogen, which may be mixed with 
the photogen first obtained ; the photogen will then, at the commencement 
of the distillation, yield a little spirit, and, towards the end, some lubricating 
oil, which may be mixed with the lubricating oil first obtained ; the lubri¬ 
cating oil will then yield a little more photogen. The spirit should finally 
have a specific gravity only a few degrees above or below 0*730, and they>7m- 
togen be within ten or fifteen degrees of 0*805 and not give off inflammable 
vapour when at a temperature of about 40° C.* The specific gravity of the 
lubricating oil will vary. A fifth of a litre of crude oil having been used, 
the number of cubic centimetres of the three fractions divided bj'* two will of 
course give the percentage volumes (in England, gallons) of each product, 
the difference between these and 100 being the loss that has occurred during 
purification or “refining.” In some cases this loss may be decreased by 
boiling together the two residues or “foots” of the acid and alkaline treat¬ 
ment and well washing the resulting “ coarse grease ” with water. The lubri¬ 
cating oil may also, if semi-solid at temperatures between 15° and 20° C., be 
further separated into oil proper and paraffin. To this end one hundred 
grammes are distilled so long as the distillate, tried in quantities of two or 
c. c. at a time, gives no crystals of paraffin on being cooled to 5° C. When 
this point is reached, the residue in the retort is poured out into a cup and 
cooled. The resulting solid fat (“lubricating grease”) is then removed, 
wrapped in a sheet of unsized paper, and placed in a small press having hol¬ 
low metal face-plates. Ice-water is now passed through the press-plates, and 
when sufficient time has elapsed for the fat to become cooled gentle pressure 
is put on the plates and the force increased slightly from time to time during 
a period of twelve or twenty-four hours. The paraffin will now be in a solid 
cake, the weight of which in grammes will be the percentage proportion 
yielded by the lubricating oil from which it was obtained. The proportion 
* Photogeu, as usually met with in commerce, does not begin to boil till heated to 170° or 
180° C. Some liquids yielded by coals, treated as above described, have a much lower boiling- 
point and much higher specific gravity. In four recent experiments with common household 
coals (Silkstone, etc.), which liad been carefully distilled at a temperature just below a low red- 
heat, I obtained products boiling at 116° to 120° C., and having specific gravities of 0-880 to 
0-920. They closely resembled the “coal-naphtha ” of the coal-tar obtained in distiUing coal 
at the high temperatures of gas manufacture. Shales found in the neighbourhood of such 
I coals, also, often yield naphtha instead of photogen. 
