Mr. Woodward states, that a series of experiments, continued during many years, has proved, that while the bladder containing the mixed gases is under pressure, the flame cannot be made to pass the safety chambers, and consequently an explosion is impossible; and even if through extreme carelessness or design, as by the removal of pressure or the contact of a spark with the bladder, an explosion occurs, it can produce no other than the momentary effect of the alarm occasioned by the report; whereas, when the gases are used in separate bags under a pressure of two or three half hundredweights, if the pressure on one of the bags be accidentally removed or suspended, the gas from the other will be forced into it, and if not discovered in time, will occasion an explosion of a very dangerous character; or if through carelessness one of the partially emptied bags should be filled up with the wrong gas, effects of an equally perilous nature would ensue.
Fig. 121.
a. The bladder of mixed gases, pressed by the board, b b, attached by wire supports to another board, c c, which carries the weights, d d. e e. Pipe to which the bladder, a, is screwed, and when a is emptied, it is re-filled from the other bladder, r. f f f. Pipe conveying mixed gases to the lantern, g g, where they are burnt from a Gurney's jet, h.
In the oxy-hydrogen blowpipe usually employed, the gases are kept quite separate, either in gasometers or gas bags, and are conveyed by distinct pipes to a jet of very simple construction, devised by the late Professor Daniell, where they mix in very small volumes, and are burnt at once at the mouth of the jet. (Fig. 122.)
Fig. 122.
Daniell's jet. o o. The stop-cock and pipe conveying oxygen, and fitting inside the larger tube h h, to which is attached a stop-cock, h, connected with the hydrogen receiver. a. The orifice near which the gases mix, and where they are burnt.
The gases are stored either in copper gasometers or in air-tight bags of Macintosh cloth, capable of containing from four to six cubic feet of gas, and provided with pressure boards. The boards are loaded with two or three fifty-six pound weights to force out the gas with sufficient pressure, and of course must be equally weighted; if any change of weight is made, the stop-cocks should be turned off and the light put out, as the most disastrous results have occurred from carelessness in this respect. (Fig. 123.)
