28 
power. Gesner gives the following results from a ton of New- 
castle coal :— 
Distilled at 1200° Fahr. for Gas. 
(Crh saan doce 6 Man oo onde Oo omeres oc 7450 cub. ft. 
PLAT or aye mievaalisdtetoe ole east shajetoteveye siefalere « 184 gals. 
GWIRA shied doom bodondo noe Shoo 1200 lbs. 
Distilled at 800° Fahr. for Oil. 
CEs ap gieinte tanta loieievefe Ute eisleintoret= fois 1400 Cub. t. 
Crnde: OMe etalon cc atreyssissttagetuside is 68 gals. 
COKE. comes stesieleie ciel oe a) sles ssi ciee 1280 lbs. 
We must now consider the influence of the atmosphere 
within the still. The atmosphere is usually one possessing very 
little or no power of combining with the body undergoing distilla- 
tion. Generally the operation is conducted so that the atmos- 
pheric air is excluded, and so that the heated body is in contact 
only with the products of its own decomposition. 
It is important that the pressure within the retort should be 
favourable. This is usually maintained as low as practicable, in 
order to reduce the time of contact of the valuable products with 
the hot vessel, by removing them as quickly as possible, and so 
preserving them from decomposition. Referring to the condensa- 
tion of the distillates, I may remark that this is to be determined 
by the temperatures at which these bodies assume the liquid state. 
The cooling must be sufficient to condense the products required, 
and still to leave them sufficiently fluid as not to impede the flow 
through the worm or other part of the cooling apparatus. 
Haying very briefly touched upon the general principles, let 
us now take more in detail a few of the most representative ex- 
amples; and, first, as an example of low-temperature distillation, 
an account of the process of distilling bituminous shale, for 
lighting and lubricating oils. 
To Dr. James Young, of Kelly, Renfrewshire, belongs the 
credit of founding this industry, which (especially in Scotland) 
has assumed very large dimensions. About the year 1848, Dr. 
(now Sir) Lyon Playfair directed the attention of Mr. Young to 
an oozing of petroleum through the top of a coal-working at 
Alfreton, in Derbyshire. There being a prospect of success, he 
commenced to refine and prepare for sale the petroleum here dis- 
covered. From it he succeeded in extracting a notable quantity 
of wax (which proved to be mainly paraffin); and he also separated 
a light oil for burning, and a heavier one for grease-making and 
lubricating purposes. The quantity of petroleum at command 
was very limited; and, after two years’ successful working, the 
supply was exhausted. Mr. Young then sought other sources of 
these oils (which are mainly hydrocarbons); and in his experi- 
ments he was guided by the ideas he had conceived relative to 
