Gas-Burners, and on the Illuminating Power of the Gases . 1 < 
i 1 mc/i. H inches. 2 focftes.- 2| inches. 
Light, - 31.3 153 241 377 435 
Expenditure, 97-4 173 216 255 288 
From which we obtain, in the usual way, the following proportions for the 
light of equal expenditures at each elevation, 
100 276 347 460 472 
Thus, by raising the flame from half inch to 2| inches, the light for a given 
quantity of gas is progressively augmented nearly five times. Sp. gr. 910. 
The explanation of the fact now substantiated will be obvious, if we hold 
in view what has been stated of the most economical mode of burning the 
gases. In Argand burners, when the flame is short, the supply of air is too 
great for the quantity of gas, and consequently the combustion is too vivid, 
and a less proportion of the gas undergoes previous decomposition. The same 
principle, applied somewhat differently, will account for the differences in the 
relative light and expenditure of jets at different elevations. For, as the jet 
is lengthened it likewise expands, and, consequently, in proportion to the vo- 
lume of gas, less of it is exposed at one time to the action of the air. 
It will be inferred from the foregoing remarks, that the length of the 
flames will have an important influence on all experiments regarding the rela- 
tive light of oil and coal gas ; and that no sound conclusion can be drawn from 
any experiments in which tins circumstance has been neglected. Let us sup- 
pose, for example, that the relation between the light of an oil-gas and a coal- 
gas jet, at their most favourable elevations (namely 4 inches for the former, 
and 5 for the latter), is 2 to 1. If the experimenter reduce the oil-gas jet to 
3 inches, keeping the coal-gas jet at 5, the proportion, as calculated from the da- 
ta we have given (p. 15.), will turn out only 1| to And, on the contrary, 
if the oil-gas jet be kept at 4, and the coal-gas jet shortened to 3 inches, the 
proportion, according to the data given above (p. 16.), will become 2| to 1. 
Of course it is not surprising that errors of this kind have been actually com- 
mitted. Peckston suggests in his work on Gas-Lighting, that the easiest mode 
to determine the illuminating power is to burn a candle against an Argand 
burner, and to alter the flame of the latter by means of the stop-cock, till the 
lights are equal, (p. 21.) A similar oversight will in part account for the very 
low illuminating power assigned by Dr Fyfe to oil-gas. He has inferred from 
the experiments formerly quoted, that the proportional light of oil and coal 
gas is as 1.42 to 1, ( Edin . Phil. Jcurn. vol. xi. p. 371.) But the coal-gas was 
burnt in its burners with a 3-inch flame, which is very nearly the most favour- 
able elevation possible ; while the oil-gas burners had a flame ot 1 § inch only, 
being just two-thirds of the elevation most favourable to that gas. If, fol- 
lowing the data given above, the necessary correction be made for an eleva- 
tion of 2£ inches, (which, however, is not even the most favourable for the 
burners Dr Fyfe employed), the proportion becomes 1.66 to 1 *. The only 
* We have no observation made at the height of If ; but we may safely 
take the mean between the results for 1| and 2, namely 403. 
VOL. XIII. NO. S5.|yJI.Y 1825. 
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