26 
SOME ASPECTS OF DESTRUCTIVE 
DISTILLATION. 
By THOMAS HOLGATE. March 3rd, 1885. 
Distillation is the term applied to the processes by which 
substances are separated, or produced and separated, by heat, 
and collected after condensation. Solid or liquid substances 
which are readily converted into vapour on the application of - 
heat are described by chemists as volatile; those which cannot 
thus be made to assume the gaseous form are said to be non- 
volatile. The quantity and degree of heat required is dependent 
upon the degree of volatility of the substance used, and of the 
products sought to be obtained. 
The apparatus employed in distillation consists essentially 
of a retort or still, followed by a cooler or condenser, and by a 
receiver. The form and arrangement of these three are subject 
to modification, to meet the special requirements of each case. 
The substance to be operated upon is placed inside the still or 
retort, to which heat is applied. The volatile products and 
educts pass over, and are cooled in long tubes kept cool generally 
by water or air. The uncondensable bodies (i.e., at the tempera- 
ture and pressure in the condenser) are collected as gases; and 
the condensable bodies are received in the liquid state into closed 
tanks or other suitable vessels. 
Distillation is, for convenience, divided under two heads— 
Destructive and Fractional. The special characteristic of the 
former is the alteration in composition of the body acted upon, 
with the production of bodies or compounds in the distillate 
which were not originally present as such. The bodies, or dis- 
tillates, so evolved are termed products, because they have not 
only been separated, but formed by the distillation. 
The special characteristic of fractional distillation is that the 
bodies which are evolved are merely separated by heat from the 
less volatile bodies which are left behind. The bodies so obtained 
in the distillate are therefore termed educts. As an example on 
a large scale we may instance the fractionation of the natural 
oils (or petroleum) of America and of Southern Russia. The 
erude oil, which is of a greenish colour as taken from the earth, 
is separated into more or less volatile oils by heating in stills, 
and collecting the distillates separately at various temperatures. 
Of the two, destructive distillation is the first for considera- 
tion, because it is by this process that the substances which are 
afterwards subjected to fractional distillation are usually obtained. 
This former is the one chosen for consideration in this paper. 
