82 
POPULAR SCIENCE REVIEW. 
the varieties of coal ; and oil gas, obtained by the distillation of 
oils. There are also two contrivances, one involving combus- 
tion in an oxygen atmosphere, and the other making use of the 
electric spark, which are both remarkable for the intensity of 
the light produced, but which are at present too costly and un- 
manageable to enter into general use. 
Tallow candles have so unpleasant an odour, they are so apt 
to gutter or melt more rapidly than the wick can consume the 
tallow, they so generally smoke and choke the wick and require 
its constant removal by snuffers, and are so little economical in 
the most important sense of the term, that they will probably 
ultimately disappear from use. They are, however, sold at so 
low a price, and possess so many apparent conveniences, that 
among the lower classes they must long retain them hold. 
The first improvement in the material used for candles dates 
as far back as 1799, when a person named William Bolts took 
out a patent by which he proposed to squeeze the tallow after 
melting, and while in the act of cooling from a melted state. 
The result of this squeezing would be to separate the tallow in 
some measure into its component parts; for, although it was not 
then known, chemists have since discovered that most animal 
and vegetable fats and oils are composed of at least two distinct 
solid bodies, one liquid oily substance, and one syrupy sub- 
stance. Of all these, one only of the solid bodies is that which 
is really valuable for illuminating purposes. It is called stearine, 
and is the really valuable material in the candle. The syrupy 
substance above alluded to is now familiarly known and exten- 
sively used under the name glycerine, and, as the reader may 
easily satisfy himself, it gives hardly any fight when burnt 
with a wick. The effect of squeezing melted tallow is to re- 
move a large part of this peculiar substance. The same pro- 
cess was afterwards effected much more completely by chemical 
action, and is now managed by blowing steam at a high tem- 
perature through the melted fat or natural oil. 
A series of brilliant experiments by two eminent French 
chemists, Chevreuil and Gay-Lussac, had so long ago as in 
1 825 cleared up the whole subject of the composition of fatty 
matters, their relative value for illumination, and the various 
methods by which their decomposition could be effected on a 
large scale ; but it is only within a very few years that it has 
been found possible to practise these methods economically, and 
separate the stearine, winch is the material best adapted for 
making candles, from the other solid contents of tallow and 
from a peculiar thick oil, which is very valuable for lubricating 
machinery, and may also be used for burning. 
Some of the vegetable oils, especially those from various 
species of the palm-tree, are now extensively used in the manu- 
