804 ON TPIE COMBUSTION OF GAS FOR ECONOMIC PURPOSES. 
best means for effecting perfect and prolonged combustion; and having attained this, 
we have to take care that the light is not destroyed by the medium of transmission. 
Glass is very transparent, but yet it destroys a notable proportion of light; and when 
the surface is ground the loss of light is often considerable 
Loss of Ligh t hy Glass Globes. 
Clear glass destroys , . . . 12 per cent. 
Slightly ground in pattern . 24 ,, 
Half ground.35 „ 
All ground.40 „ 
Opiil glass.GO „ 
And lastly I have to refer to the methods which are adopted for estimating the value of 
the light of gas. These are as follows :— 
1 . By observing the durability of a jet of gas of a given height from an aperture of 
a given size. 
2. By ascertaining the pressure necessarj^ to obtain a flame of a given height from 
the same jet. 
3. By noting the height of the jet when the gas is burning from an aperture of a 
given size and at a uniform pressure. 
4. By ascertaining the quantity of air which is required to destroy the light or a 
flame burning at a given rate. 
5. By comparing the light wilii a standard flame. 
The first method of testing the illuminating power of gas was often used by the late 
Dr. Fyfe, of Glasgow, and when it was conjoined with another test, namely the amount 
of condensation by chlorine, it was much relied on. The jet which he used had a dia> 
meter of the l-33rd of an inch, and the flame wns kept at uniform height of four inches. 
In this way he found that a given volume of gas of different qualities burnt out in dif¬ 
ferent times, thus:— 
Durabilify of a Cubic Font. 
Common Newcastle coal gas . 50'5 minims. 
Wigan canned.57’0 „ 
Lesmahago.G5-0 „ 
Wemys.75-0 „ 
Boghead.81‘0 „ 
Secondly, he further ascertained that the pressure necessary to make a gas burn from 
an aperture of a given size, and with a flame of a given height, vras also the exponent 
of the quality of the gas; for the better the gas the less the pressure at which it burns, 
and the less also is the consmnption to produce aflame of a given height. For example, 
with a jet l-40th of an inch diameter, and a flame 5 inches high, the following w'ere 
the rates and pressures of different gases:— 
Pressure, 
Consunip. per 
Specify Gravity 
Inch. 
Hour, Cub. Ft. 
ot Gas. 
0-6 . 
. . . 0-G7 . . 
. . 0-811 
0-8 . 
. . . 0-77 . . 
. . 0-729 
1-0 . 
. . . 0-8G . . 
0-552 
1-2 . 
. . . 0-94 . . 
. . 0-595 
1'4 . 
. . . 1-03 . . 
. . 0-551 
1-6 . 
. . . 1-09 . . 
. . 0515 
1-8 . 
. . . 1T5 . . 
. . 0-486 
2-0 . 
. . . 1-21 . . 
. . 0-461 
His deductions from these results were, that the specific gravity of the gas—or, in 
in other -words, its quality—was inversely as the square roots of the pressures, and that 
the volume consumed in a given time was as the square roots of the pressures. He 
relied so much on this test, that he thought it capable of taking the place of both the 
meter and photometer. 
The third method of ascertaining the value of gas is by observing the height of a 
flame at a given pressure from a jet with an aperture of a given size. This method has 
has been adopted by Mr. Lowe, and it goes by the name of Lowe’s jet. It is, as you 
perceive, a modification of the preceding, for a poor gas will burn wuth a shorter flame 
