ARTIFICIAL ILLUMINATION. 161 
consumed per hour; we may even reach as much as 25 candle power 
with some of the largest sizes in use. In another form of burner, the 
Argand, where the air supply is controlled by a chimney, a higher 
efficiency, up to 3°2 candle power per cubic foot, is realised. The 
burner before you is known as the “London Argand”; it is the 
burner used in the tests of London gas, the Government requirement 
being that when 5 cubic feet of gas, as supplied by the London com- 
panies, are burnt per hour in a lamp of this type, it shall give an 
illumination of 16 standard spermaceti candles. 
(2.) The material of which the burner is made has some influence 
onits efficiency. The old iron burners formerly used were bad, because 
iron, being a conductor, abstracted the heat and reduced the temperature 
of the flame, thus diminishing the illuminating power. All modern 
burners now have non-conducting tops, generally of steatite, to 
prevent loss of heat in this way. 
(3.) The pressure of the gas supply is an important factor in 
the illuminating power, for high pressure may evidently cause an 
excessive rate of flow of the gas into the air. Pressure therefore, 
beyond an amount, generally equivalent to a height of about three- 
quarters of an inch or an inch of water, must be checked by 
mechanical means. Gas governors are in use for this purpose, the 
principle on which they act being exceedingly simple. If the pressure 
of the gas passing through is too great, it lifts a carefully balanced valve 
and automatically closes the aperture from which the gas is emerging. 
We may control our gas supply in this way, either at the meter or by 
simple little governors such as the very inexpensive but effective one 
which I have here, at every gas jet. We can thus effectually prevent 
any abnormal out-rush of gas from the burner such as results from 
a gas company giving us, as they sometimes do, a two-inch or three- 
inch pressure, and which produces the well-known roaring of a gas 
flame with its extravagent consumption of gas and comparatively 
poor light, due to the “ Bunsen ” effect. 
(4.) Another cause of poor light at the burner is the poverty of 
the gas itself. For good light we require incandescent carbon, and 
therefore we cannot expect satisfactory light if there is too little 
carbon in the gas. London gas companies have considerable diffi- 
culty in sufficiently enriching their gas to the standard of 16 
candle power. Formerly a certain admixture of cannel-coal was used 
which gave a higher proportion of carbon in the gas than ordinary coal 
alone. Cannel-coal, however, is now very scarce, and the gas companies 
obtain the necessary enrichment by other means, such as the addition 
of a certain amount of the vapour of benzine, or of gas obtained by the 
“splitting,” as ib is called, of petroleum oils. k 
The “albo-carbon” system of enrichment at the burner itself, which 
was introduced some ten years ago, has had a considerable amount of 
success. You have a burner before you. This chamber contains ‘a 
quantity of naphthaline or “albo-carbon” as it is called, which is one of 
the solid products of the distillation of coal, and when the gas has been 
lighted at this small No. 1 burner, the heat after a time melts and 
vaporises the naphthaline, which is very rich in carbon, and the gas, in 
passing through the chamber, takes up a portion of the naphthaline 
22 
