1242

THEORY AND PRACTICE OF ENGINEERING. Rook IL

Litmus paper dipped in water is a good test for sulphuretted hydrogen : the darkpurplish blue, if this gas be present, changes its colour to red ; if carbonic acid be present,bv adding a little lime water to it, an effervescence will take place when a few drops of

muriatic acid are added. Hydrogen gas affectsboth silver and mercury ; on mercury it pro-duces a black film, and it soon tarnishes theother metal.

Six tallow mould-candles, weighing a pound,will burn forty hours, if lighted in succession;a gallon of sperm oil, burnt during the sametime, will give a light equal to 15 such candles;500 cubic inches of coal gas give a light foran hour equal to one of the above candles, so thatit would require 20,000 cubic inches to beequivalent to the 6 mould candles, or between11 and 12 cubic feet of gas; the cost of whichis estimated at about l}d. per cube foot, as de-livered for burning.

Oil Gas is generally admitted to be morepure than that made from coal, and the processfor its manufacture is very simple : a furnaceis provided to heat the retort red-hot, thefront of which is a cylindrical ca'st-iron vessel,with a cover fitted to its mouth, so as to closeit completely : the retort is partly filled withcoke and broken brick, so that the oil, whichfalls by drops upon the heated substance, maybe exposed to as large a heated surface aspossible. The oil is contained in a coppervessel, and permitted to drop regularly througha pipe upon the heated matter in the retort,where- it is decomposed, after which the gasesascend into the cistern or condenser above,formed of two iron vessels, one within the other,and the space between is filled with cold water,for the purpose of condensing the products ofdistillation.

Mr. Beale has contrived an apparatus for theproduction of a powerful light, by the con-sumption of the refuse tar of the gas-works :it consists of an external copper case, at thebottom of which is a cock to discharge thefluid, should it rise above the required level.The tar is placed in the cylinder, and allowedto mount in the pipe attached, which it doesby the pressure of the atmosphere, on the prin-ciple of the Argand lamp; at the bottom ofthe pipe is another, connected with a vessel, inwhich air is contained under a pressure of1^ pound per square inch : this by means of asmall cock can be opened or shut at pleasure.When the tar is lighted, a small lambent flameis first obtained, and when the compressed, airis admitted, it burns with a strong vivid whitelight.

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Fig. 1953. BEALE’S LIGHT.

C-IIAP. XXL

STEAM CONSIDERED AS A MOVING POWER.

From the elasticity of steam, which arises from the latent heat it contains, very earlyadvantage was taken of its power, and it is now universally applied for the purpose ofmoving and impelling machinery ; like all gaseous fluids, if steam be separated from the