Modern magic lanterns; a guide to the ... - Yesterday Image

HOME-MADE OXYGEN, GAS HOLDEES, ETC. 21To use the gas, the jet can be connected with b by indiarubberpipe, or a second stopcock can be fitted to the uppercylinder as the gas outlet. Weights must be placed on theflat top of A until the desiredpressure is obtained. Smallgas holders of this pattern are1^easily constructed of galvanisediron and will last a lifetime.We have seen a veryefficient one made of two ofthe large cylinders in whichpaint is supplied. Anotherform of gas holder is shownat Kg. 15, in which a is theinlet and outlet for the gas ;B, a stopcock which is openedduring the filling of the holderto allow the displaced waterFig. 15. A Gas Holder.to escape ; c, a pipe throughwhich water, under more or less pressure, is supplied todrive out the gas when it is required for use.One or other of these forms of gas holder are still largelyused where the limelight is constantly wanted in the sameplace, as, for instance, in theatres, in photographic enlargingestablishments, etc.Oxygen gas is generally prepared in small quantities byheating together in an iron vessel a mixture of chlorate ofpotassium and oxide of manganese. Both these compoundsshould be fairly pure, it being particularly important thatthe manganese oxide is not adulterated in any way; thepresence of, for example, carbon in any form in it being mostdangerous. The cheapest (and worst) form of generatortakes the form of a conical sheet-iron or copper vessel, whichis very difficult to properly clean, and is unprovided withany safety-valve arrangement. Mr. Chadwick, to whomlanternists are indebted for many ingenious and practicalimprovements, has introduced two forms, either of whichare much more suitable. One of these is shown in Mg. 16.In this, the handle at the top being pulled over, the bellshapedtop, which, like the rest of the apparatus, is of cast