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I IO CURRENT TOPICS.
giving power of gas is proportional to its heat value; or with the same gas, the ligilt emitting power of the incandescent mantle is proportional to the number of heat units fed to the burner per unit of time. This is not an exact law, but a serviceable rule. The true value of gas, then, both for light and heat can be measured by its calorific power, this is the only logical measure. A gas having a calorific value of 5,2oo cal. per cubic metre is recommended as the standard. The latest designs of burners for heating and lighting require that the gas should have an approximately constant composition, since the maximum efficiency of the burner is only obtained when the relative amounts of air and gas are closely regulated. Water gas may be added to prevent excessive variations in calorific value. Gas should be free from hydrogen sulphide, cyanogen, and ammonia. The gas producer should choose that coal which on distillation yields the greatest part of its heat value in a gaseous form.
๐ SIMILAR VOLUMES
The foregoing t:lble contains the metals whose coefficients of dilatation are kno~r with sufficient accuracy for the purpose of testing the truth of the laws. 'I& above t:Lbk shon-s that the lengths of the oscillatirjns are in the inverse ratio of the melting points, and that the products of thcsc
## Blau Water Gas for Industrial Purposes. A. MEADE. (J. Gas Lighting, cxvii, 83.)--The industrial use of water gas has made considerable progress on the continent of Europe. Its most important property is its very high flame temperature. With preheated air, a temperature above the melting-point o