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The Optical Magic Lantern Journal and Photographic Enlarger.
building. On entering the door, the wind furnace was situated in a corner on our left, the large cast-iron purifier standing between the furnace and the door, and immediately facing us stood the bench with special appliances for fitting up the retorts. These consisted of
mercury bottles, into which were screwed pieces _ | by the aid of a hand-pump.
of 13-inch gas barrel four-feet in length, having a male thread cut on the end furthest from the bottle. Four such retorts were filled with oxide of manganese broken in small pieces (not in powder or grains) and placed in the furnace, the upper end of the outlet tubes being screwed on to the pipes leading to the purifier by means of union joints with special large wings to give leverage in screwing up. The fuel was then stacked in round the retorts and lighted, after which the process of gas-making went on slowly, and needing no attention for some considerable time; there was no rush of gas as in making from chlorate of potash; the process was slow, quiet, and so far as my experience went, free from danger.
The joints connecting the retorts with the pipes leading to the purifier had to be screwed up very tightly as the gas was made under pressure, the weight on the gasometer remaining the same as when the gas was being consumed. The gasometers were of the ordinary type, consisting of a bell containing the gas, which ascended or descended into a well of water. The bell was arranged in a rather unusual manner, as it was divided into two portions by
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a horizontal division across the centre, the lower portion being to contain the oxygen, while the upper was filled with a quantity of water giving
the requisite pressure. The hydrogen gasometers were in another part of the building, and were filled every day with ordinary carburetted hydrogen from the main, which was forced in
Originally pure hydrogen was used, being generated in two large leaden vessels about the size and shape of nine gallon casks, but although there was a little increase in the light in this case, yet the difference was not sufficient to justify the extra trouble and expense.
Before starting the lanterns, the pressures in the different gasometers were carefully tested by means of two water gauges situated in the optical room.
Although other gas containers have to a great extent taken the place of gas-bags, yet there are many exhibitors who still hold fast to the old method of obtaining the lime-light, and, for the benefit of these, I should like to say a word or two about some forms of pressure boards. In the infancy of the lime-light two separate boards were used, as all lanternists know, but this mode was open to such serious objections that it was felt that some improvement must be made, and the double pressure board was devised in which the two gas-bags were used under one set of weights. One form which was used for a considerable time, and which is still used in some places of amusement, will be found in Fig. XI.