Fahrenheit scale to absolute temperature in Fahrenheit degrees is to add 460°. "The object now to be attained is to condense the laws of Boyle and Charles into one simple expression. "Clerk-Maxwell neatly combines them in the following expression: The product of the volume and pressure of any gas is proportional to the absolute temperature.' Let V, P, T be the observed volume, pressure, and temperature on the absolute scale, and Vo the volume at standard pressure Po, and standard temperature To on absolute scale; then то Ро is a constant quantity, and if the standard be 30 inches barometer and 520° thermometer, the standard absolute temperature becomes 17-333, and the formula for dry gases V P 17.333 But coal-gas is usually measured over water, and if it be considered necessary to correct for the varying pressure exerted by water vapour at various temperatures, we must slightly modify the above formula. The original formula can be used if it is understood that P represents the observed pressure, minus the tension exerted by water vapour at the temperature, T, and Po the standard pressure, minus 5178, which is the tension of water vapour at the standard temperature, 520 (460 + 60). "The Gas Referees' formula (preserving the symbols) is: Or more simply, in order to correct a volume of dry gas to the normal temperature and pressure of 60° F. and 30.0" bar., multiply 17.333 by the observed pressure and then by the volume, and divide by the observed temperature + 460; or calling temperature T, pressure p, and volume V, In the case of a moist gas (Referees' formula), multiply 17.64 by the observed pressure, minus the tension of aqueous vapour at the observed temperature, then by the volume as before, and divide by 460 + t. The formula being 17·64 × (h - a) × V We will now describe how to utilize these two formulæ by an example showing the methods of correcting dry and moist gas respectively: 1,000 cubic feet of gas are measured at a temperature of 55° F., and under a pressure of 30.6 inches, what would it occupy at the standard temperature and pressure of 60° F. and 30.0"? Then 17.33 × 30.6 × 1,000 460 + 55 = (515) = 1029.7 cubic feet. Now, supposing the same gas was measured in a moist condition, the calculation would then be 17·64 × (30·6 — ·4329) × 1000 1033 cubic feet, which agrees with the number given in the Gas Referees' table. CHAPTER XX. THE COMPOSITION OF COAL-GAS. URIFIED coal-gas is a mechanical mixture of hydrogen, PURIFI carbonic oxide, and certain hydrocarbons, which are capable of existing as gases at ordinary temperatures; of these hydrocarbons marsh-gas figures prominently. There are also present certain hydrocarbons which occur in the gas in a state of vapour, and which, if isolated, would not be capable of existing in the gaseous form at ordinary temperatures. Nitrogen is also found in small quantities, and frequently oxygen is also present; but the presence of the latter gas is due to the drawing in, either accidentally or otherwise, of atmospheric air, as it is not produced by the distillation of the coal. There are also traces of sulphur and certain other compounds of a phenolic character. The hydrocarbons upon which the luminosity of a coal gas flame entirely depend, are divided in the analysis of such gas into two groups-saturated and unsaturatedaccording to their behaviour with a solution of bromine in bromide of potassium, which has the power of absorbing the hydrocarbons termed "unsaturated," but not affecting in diffused daylight the gaseous members of the saturated series of hydrocarbons; concentrated sulphuric acid acting in a similar manner to bromine. Hydrocarbons are compounds containing carbon and hydrogen only, and they are divided into several series, in each of which the proportion of carbon to hydrogen bears a definite ratio. Taking the letter C as representing twelve parts by weight of carbon, and H as denoting one part by weight of hydrogen, the hydrocarbon series present in coal gas may be represented as follows: n standing for the number of times twelve of carbon is found in the body. n (1) The paraffins-C, H2+2. Methane (or marshgas) and ethane may be taken as examples. (2) The olefines—C2 H2 n° (3) The acetylenes-C, H2n - 2. (4) The benzenes-C, H2 - 6. (5) Naphthalene-C, H2- 12. The paraffins constitute the saturated hydrocarbons present in coal-gas, and the term “saturated" is applied to them because they contain the maximum amount of hydrogen combined with the carbon. In coal-gas the simplest member of the paraffin series, methane, is certainly one of the most important constituents, while minute traces of three other members of the same series are often present, viz., ethane, propane, and butane. "Among the unsaturated hydrocarbons present in coalgas, ethylene and benzene vapour play the most important part, while extremely small traces of propylene, butylene, acetylene, crotonylene, and naphthalene can be detected by working with very large volumes of gas. For all practical purposes we may look upon unenriched coal-gas as containing methane, ethylene, and benzene vapour, as the hydrocarbons which, during combustion, endow coal-gas flames with luminosity." Ordinary 16 or 17-candle gas, made from caking coal, according to Mr. L. T. Wright, would have something like the following composition: Richer gases made from cannel coal generally contain a large proportion of the absorbable hydrocarbons, but a large percentage of these docs not always mean great luminosity. The following are recent analyses of coal-gas, as supplied by the three London companies serving the metropolis, as given by Professor Lewes : It will be necessary to briefly discuss some of the perties of these constituents. pro The illuminating power of marsh-gas, when burnt in the standard Argand burner, is given by Mr. L. T. Wright as 52 candles per 5 cubic feet; but, according to Professor Lewis, a far higher illuminating value can be obtained from it at a higher temperature, i.e., when consumed in a regenerative burner, where it becomes nearly as luminous as |