ARTIFICIAL LIGHT. 
85 
kept at some distance from the flame, so that only the vapour in 
a heated state is ignited. What actually burns is thus a gas ob- 
tained from the paraffine oil by the application of moderate heat. 
Many other naphthas (camphine among the number) have 
from time to time been introduced and tried hi lamps ; but it 
is only lately that any satisfactory result has been obtained. 
A disagreeable odour, not belonging to paraffine itself, and pro- 
bably not essential to the oil, still characterizes the naphthas 
commonly prepared and sold; but this can be removed by certain 
processes of purification, and it may be expected that the con- 
sumption of paraffine oil will greatly increase. The paraffine oils 
have this great advantage over turpentine, and other light oils 
obtained in a similiar way, that they do not burn when exposed 
directly to flame, and they do not soil linen or adhere to the 
fingers. 
Pure paraffine is itself a soft light solid, without taste or 
odour, melting at a temperature little above that of the blood 
(112° Fain.), and burning with a clear white flame, without 
smoke or ash. It has already been made into very beautiful 
candles ; but the manufacture at present has not attained great 
importance, although as much as 300 tons were employed in 
this way two years ago. The cost of obtaining pure paraffine 
is the present cause of this delay in the progress of the manu- 
facture. 
The minerals which yield paraffine oil on exposure to a low 
heat in a retort will yield to destructive distillation at a higher 
temperature a very large quantity of gas (chiefly carburetted 
hydrogen), which takes fire readily on exposure to flame ; but 
those best adapted for the one purpose are least fitted for the 
other. Bituminous shales are best for paraffine oil, and coal for 
the manufacture of gas. The gas thus obtained, when freed 
from cei'tain impurities, burns with an intense and nearly pure 
light, and is the common gas supplied for burning. 
So long ago as in the year 1659, and again about eighty 
years afterwards, gas of this kind, issuing naturally from the 
ground in the neighbourhood of coal-mines, had been the sub- 
ject of experiments of a scientific nature, which were communi- 
cated to the Royal Society, but no practical result was obtained 
till in 1792 Mr. Murdoch lighted his own house with a similar 
gas, and was shortly afterwards successful in lighting in the 
same way the factory of Messrs. Boulton and Watt at Soho. 
It was not till 1813 that any important step in lighting towns 
on a large scale was made, but from that period to the present 
day the consumption of gas for purposes of illumination has 
been increasing with such enormous strides that scarcely a town 
in the civilized world is now unsupplied with this admirable and 
useful means of turning night into day* 
