Dr. Pilayfair’s Lecture on the Great E'rhibition of 1851. 33 
their more expensive substitute, wax, were generally used till 
within the last twenty years. The tallow itself was long ver 
impure, containing cellular tissue, which was only partially re- 
moved in the form of a scum, known as “ cracklings.” This 
impurity rendered the light unsteady, and obstructed the wick. 
The old method of purification still largely used in this conntry, 
though superseded on the continent and in Dublin, whence such 
good tallow candles were exhibited, has been displaced by a pro- 
cess of treating with sulphuric acid the tallow melted by steam. 
Much of the smell is thus removed, and a larger amount of purer 
tallow is obtained. The researches of Chevreul had shown that 
fats consist of fatty acids, combined with a kind of sugar named 
glycerin, which it was important to remove; this glycerin, re- 
moved in candle-making, is now used for liniments in cutaneous 
affections, and is employed as a remedy in deafness and rheuma- 
tism. By boiling with lime, an insoluble soap is formed, while 
the glycerin remains dissolved in the water. This lime-soap, de- 
composed by a stronger acid, yields the fatty acids in a pure state. 
But there are generally two solid acids mixed with the fluid one ; 
and the latter is easily removed by pressure, the solid fats remain- 
ing. ‘The solid acids are made into the beautiful candles errone- 
ously called “stearine.” Various difficulties occurred in this 
manufacture. The solid acids, crystallizing rapidly, were ill 
adapted for candles; but the introduction of arsenic in small 
quantity prevented the crystallization. The public were justly 
alarmed at this dangerous practice, and the manufacture was 
threatened with extinction, when it was found that a small per- 
from the air by its fiery prison, is charred, aud diminishes t 
light. If the wick could be made to turn outwards, it would 
reach the exterior air and be consumed, whilst the glass formed 
by the action of the borax on its ashes would also be removed. 
This beautiful scientific fact was attained by the introduction of 
plaited and twisted wicks, the tension of the threads foreing the 
wick to curl outwards to the exterior of the flame, where it is 
rapidly burned. 
Srcoxp Sxnims, Vol. XIV, No. 40.—July, 1852. 5 
