The relative illuminating value of different oils and of coal-gas formed the object of a series of careful experiments recently made by Dr. Stevenson Macadam, lecturer on chemistry in Edinburgh; and the following are some of the results, bearing more especially on the relative cost of the various sources of artificial light. The standard of comparison is the sperm candle above described; an hour of such a candle is assumed as the unit of light supply, and is called a the price of tallow, composite, and paraffin at 6d., 8d., and is. respectively— Tallow will give 7.29 candle-hours for 1d.
Composite " 6 19 " Paraffin " ., , .. . . . . .
Animal and Vegetable Oils.—Burnt in a lamp— Sperm oil gives 4 69 candle-hours for 1d.
Rape-oil " ............ _ ............7.18 " Whale-611 " 8.56 " Burnt in an argand lamp Sperm-oll gives 8.99 candle-hours for 1d. Rape-oil " .14.17 " Whale-oil " 15.42 " Paraffin 28. per gallon, paraffin oil gives 53.33 candle-hours for id.; at 1s. ad. per gallon it gives 71.11 candle-hours for experimenting with coal-gas, the standard assumed was a gas which, with a burner consuming 5 cubic ft. an hour, gave the light of 28 sperm candles. Thii burner is called No. 5, and the others, Nos. 4, 3, 2, 1, 0.5, are such as under a regulated pressure pass 4, 3, etc., cubic ft. an hour respectively.
standard gas at 58. per 1000 ft.
No. 5 jet gives.... 93.33 candle-hours for 1d.
. " 4 ." 86.66 " 3 ,, 76.66 " ,, 65 50 dr....33.33 " • Coal-gas is thus cheaper than paraffin, when the gas is burnt in large jets; but dearer in small jets.
fit is necessary to observe that giving equal quantities of light is not the real measure of economy, because no one is contented to take no more light from gas than from other modes of lighting; and the gas-lights being fixed, more light is requisite in order to compensate the loss of the convenience afforded by a movable light. Five feet per hour
of 15 candle-gas will fully supply the place of a pair .of sperm candles, costing 8d. for 10 hours' light; while the gas at Ss. per 1000 ft. would only cost 8d. for the same time, and would yield a light 7 times as great.
The use of gas for heating and. cooking is becoming extensive. Its great recom mendations are facility of regulation, readiness of application, and perfect cleanliness. In roasting by gas, the juices are retained in the meat to a greater extent than by the ordinary process; while in all the operations, the heat can be regulated with so much nicety, as greatly to aid the cook in presenting the food in the most wholesome and agreeable condition.
Besides brilliancy of light, safety and cleanliness attend the use of gas. Explosions under ordinary circumstances are hardly possible—the escape of gas is quite disagree ably perceptible by the smell when there is one tliree-thpusandtll part present in the atmosphere; and there can be no explosion unless with, at the least, 200 times that quantity, or 1 part in 15. Such accumulations will, and do undoubtedly, take place in confined situations, bin ordinary precaution in avoiding the use of a light will avert the risk of accident. Gas, having a tendency to ascend, escapes near the ceiling of an apartment are more likely to form an explosive mixture than escapes occurring low down. Repealed accidents have happened through, forgetfulness of this. It should be remembered that the-situation must be considered a confined.one when the gas is pre vented from ascending freely. The standard work on gas-lighting is that by the late Samuel Clegg, Jun., son of the inventor of the gas-meter, published by John Weak, London. There is also a smaller work by the same publisher, written • by Samuel IIughes, C.E.