during distillation, the quantity produced is infinitesimal. When the lime is saturated it is removed, and fresh supplied; but the iron, after use, can be reconverted into oxide by exposure to the atmosphere, and used repeatedly. When iron is used a separate lime purifier is necessary to remove carbonic anhydride. The last traces of ammonia are removed before passing to the gas holder, by passing the gas through dilute sulphuric acid, or up through the interior of a tower having perforated shelves covered with coke in small pieces, through which a constant supply of fresh water percolates. This washing removes some of the more condensable hydrocarbons, and lessens the illuminating power of the gas. Before the gas passes from the condensers into the purifiers, it passes through a kind of pump, termed an exhauster, driven by steam power. This action relieves the retorts from the pressure of the gas passing through the hydraulic main, etc. It diminishes the deposit of graphite in the retorts, and lessens leakage in them, should there be any flaws. It also has the beneficial effect of producing a gas of a higher illuminating power, since the relief of pressure in the retorts produces a more favorable condition of combustion. [Illustration: THE DISTILLATION OF COAL.] The following are some of the bodies produced in the manufacture of gas, namely, acetylene, _g_, the carbonate, _s_, chloride, _s_, cyanide, _s_, sulphide, _s_, and sulphate, _s_, of ammonium; aniline, _t_, anthracene, _s_, benzine, _l_, carbonic oxide, _g_, carbonic anhydride, _g_, carbonic disulphide, _l_, chrysene, _s_, cumene, _l_, cymene, _l_, ethylene, _g_, hydrogen, _g_, leucoline, _l_, methyl-hydride, _g_, naphthaline, _s_, nitrogen, _g_, paraffine, _s_, phenylic alcohol, _l_, picoline, _l_, propene, _g_, quartene, _g_, sulphureted hydrogen, _g_, toluene, _l_, water, _l_, xylene, _l_, etc. The most of the above solid and liquid substances, with the letters _s_ and _l_ written after, are removed by cooling the gas in the condensers, and the gaseous substances marked _g_, that are injurious in the consumption of the gas, are removed by purification. The impurities in the gas may consist of ammonic carbonate and sulphide, carbonic anhydride and disulphide, nitrogen, oxygen, sulphureted hydrogen, and water in the form of vapor; and acetylene, ethylene, and the vapors of the acetylene, ethylene, and phenylene series of hydrocarbons are the illuminating ingredients diluted with carbonic oxide, hydrogen, and methyl-hydride. The approximate percentage composition of coal gas is: H, 45.6; Me, 34.8; CO, 6.5; C{2}H{4}, 4; CO{2}, 3.6; N, 2.4; C{4}H{8}, 2.3; SH{2}, 0.3, etc.--_Hugh Clements in English Mechanic._ * * * * * =A Short History of Petroleum.=