GARUM, is a name which has been applied by medical writers to a pickle, in which fish had been preserved. The garum of the ancients was greatly esteemed as a delicacy at their tables.
GAS, is a name which was given by Van Hclmont to aeriform or elastic fluids. See CnEmist RIC, and GASES.
GAS LionTs, is the name given to the artificial light produced by the combustion of inflammable gases, obtain ed from the destructive distillation of pit-coal, and several other combustible bodies.
The late Mr W. Nicholson has very properly observed, that during the combustion of oil, tallow, wax, E-tc. in pro ducing light, the same change takes place among their respective elements, which would have been produced by subjecting them to destructive distillation, the inflamma ble gas being the substance furnishing the light which they afford. The only difference, therefore, between the light of candles, lamps, Sic. and the gas lights, is, that in the former the decomposition of the substance,cnd the conse quent evolution of the inflammable gas, is effected by its own heat. in the gas lights, the decomposition is effected in a close vessel by a separate fire ; and the gas given out, after being washed, is conducted to a reservoir, from whence it is drawn through small apertures, where it is set on fire. In candles and lamps, the inflammable gas, which is the source of the light, is more or less accompanied with smoke, which, if not burnt, produces a cloudy yellow flame. In the Argand lamp, where the supply of oxygen is great, the smoke is burnt, which of itself_ furnishes some light ; but the brilliant light is more to be attributed to the pu rity of the inflammable gas after the cloudy matter is re moved.
All substances, whether animal, vegetable, or mineral, consisting of such proportions of hydrogen and carbon as to furnish the inflammable gases, are capable of furnishing artificial light by decomposition. The gases produced in the operation are carburetted hydrogen, oiefiant gas, and in some cases carbonic oxide and pure hydrogen.
We are indebted to Dr Henry for some valuable facts, derived from his experiments, upon several bodies afford ing inflammable gas by destructive distillation. The fol
lowing is a small Table from his paper, exhibiting the re lative value of the gases from different substances in pro ducing light.
It is found, as we should naturally infer, that the quantity of light furnished is as the quantity of oxygen required to consume the gas. The carbonic oxide, which is already half saturated with oxygen, produces the least light, while the olefiant gas, as will be observed in the Table, requires the most. The gas from moist charcoal contains about 73 per cent. by weight of carbonic oxide, the rest being prin cipally hydrogen. On this calculation, the specific gravi ty of this gas comes out 6, hydrogen being 1. Its specific gravity by experiment, according to Cruickshank, is 5.4. Those from oak•wood and dried peat probably differ but little from the latter. This, however, might be ascertain ed nearly, if we knew their specific gravities. The gas from cannel coal, when purified in the 11141111er hereafter to be directed, consists almost wholly of catbu•etted hydro gen. its specific gravity, derived bv calculation from Dr Henry's table, is 6.5. Carburetted hydrogen, on the au thority of Mr Dalton, is 7.5, hydrogen being 1. If Dr Henry's experiment be correct, and 7.5 be the true speci fic gravity of carburetted hydrogen, then the cannel coal gas must contain free hydrogen, from its specific gravity being less than that of carburetted hydrogen. The car bonic oxide, sulphuretted hydrogen, and sulphurous acid, which the coal gas will contain, if not purified, would con tribute to increase the specific gravity.
Olefiant gas produces the most brilliant light of any other gas, which is to be attributed to its consisting entirely of hydrogen and carbon, and its great specific gravity. The gases from the distillation of lamp oil and wax, in the way the coal is distilled, will be seen in the table to exceed the coal gas ; and that Won) wax nearly approaches the olefiant gas in the consumption of oxygen, and in the property of producing light. The substances, however, affording ole fiant gas are too expensive to he applied to the production of light by the process used for obtaining coal gas.