aving got fire-balloons out of hand, I will now have some words with you about air-balloons, usually so called, though ‘gas-balloons’ would be a more appropriate designation. Before describing how to make an air-balloon, suppose we gossip a little about the science of the thing.
Of gases there are many sorts, as you will become aware when a little advanced in your chemistry. Atmospheric air is a mixture of two gases, as probably you know—four measures of nitrogen to one of oxygen, roughly speaking; though were we describing the composition of atmospheric air in an exhaustive manner, we should have to chronicle the presence of numerous other gases besides oxygen and nitrogen, and some vapours; all, however, in quantities so extremely small that we need take no account of them here. Some gases are lighter than atmospheric air, some heavier, but it is evident that those only which are lighter can be employed for ballooning. The very lightest of all gases is hydrogen, which therefore is the very best gas for filling balloons. It is seldom now employed, however, coal-gas being usually substituted, on account of its being ready to hand, so to say, in every place where coal-gas illumination is practised.
Here, perhaps, some young gentleman will wish to inquire why it is I employ the ordinary name, coal-gas, instead of a chemical name. The reply is simple. Coal-gas always means gas from coal, but when I tell my readers that coal-gas has not necessarily always the same composition, although the same coal be used, they will see that no unchanging chemical name for it is applicable. According as the gas retort is heated more or less, so will the resulting gas differ in composition—not a difference as to nature of components, but as to quantity. Coal-gas must always be a combination of carbon with hydrogen, but the amount of carbon to a given amount of hydrogen may vary within wide limits. If coal-gas be required for illuminative purposes, the object of manufacture will be to make it as rich in carbon as possible. Now, the richest gaseous combination of carbon with hydrogen is olefiant gas, but it would be the worst quality of coal-gas for balloon inflation. If olefiant gas be transmitted through a white-hot iron pipe it expands in volume, thus showing what would have happened had it originally been produced in a white-hot iron retort. A gas manager doing duty in one of our seaport towns once told me that he always managed to have expanded gas—we may call it adulterated gas—for night street service. It was good enough, he explained, for drunken sailors, and nobody else was about.
Probably you youngsters will generally use coal-gas for filling your balloons, it being so handy. I would prefer that you did not, but use hydrogen instead, because not only is the making of hydrogen chemically instructive, but a balloon of given size will lift at least half as much again as it would if filled with gas from coal taken as one finds it. Besides, general though the use of coal-gas illumination has become, it may happen that some boy is staying at a country house where coal-gas is not available, for all which reasons I shall begin by giving directions for the production of hydrogen on a sufficiently large scale, and easily.
IV.—HOW TO PREPARE HYDROGEN GAS.
There are many ways of preparing hydrogen. I shall offer you the choice between two. Both are equally good, and you will discover for yourselves which is the easier under your own special circumstances. No. 1 consists in acting upon zinc or iron—zinc is best—with a mixture of one part of oil of vitriol, measure, and six parts of water, also measure. No. 2 consists in passing steam through a red-hot iron pipe, loosely packed with fragments of iron—say iron nails. If oil of vitriol be available in the out-of-the-way country house where you are assumed to operate, I recommend you to follow plan No. 1. So now about the apparatus. Two large wide-mouthed pickle or preserve bottles, with bungs to match, and a few feet of small leaden gas-pipe, are all that you will require, and you must arrange your apparatus in the following fashion. ([Figs. 1 and 2].)
Figs. 1 and 2.
You will here observe that one bottle is represented as larger than the other. We may call it the generator. Into it a good handful of zinc fragments having been put, or in defect of these a handful of small iron nails, and the cork thrust in tight, the mixture of oil of vitriol with water is to be poured down the upright tube at a, which you will observe has been reamed out into a sort of funnel shape by thrusting into it a conical piece of wood. It is worth while here to remark that though a large preserve bottle answers very well as a generator, yet a copper vessel answers much better, the gas development being much faster, on account of a galvanic condition, due to the contact of copper with zinc, and which on this occasion I do not consider necessary to write more about.
