A Few Cautions.
It is a very sensible idea to keep spectators away from the generator, as they are very apt to strike matches or tread on the tubes, in spite of warnings to be cautious, for if there should be a leak, even so slight as to be hardly detected, it would cause a violent explosion, and as hydrogen is both odorless and colorless, this could easily happen without being noticed. This is probably the origin of the apparent secrecy with which a lead burner usually surrounds himself.
If an explosion should occur in the tubes and they should catch fire, the operator must have presence of mind enough to reach the gas cock on the generator and close it. If gas explodes in the generator, all that can be done is to dodge the flying pieces and make a new generator. If such an incident should occur and vitriol should spatter on the person doing the work, or his assistant, a solution of bicarbonate of soda or common washing soda should be at once applied to the wounds. If that cannot be procured, grease or oil of some kind should be used without delay, rubbing it on the spots where the acid burns, and this will neutralize the acid and so prevent it doing further damage. There should be no trouble of this sort in the hands of a careful workman. The watchword should be, “Test the gas before using.” If this is done, explosions will never occur.
CHAPTER III.
HYDROGEN GAS.
This element was discovered by Cavendish in 1766, and was called by him inflammable air. The name hydrogen is derived from two Greek words, one signifying “water” and the other “to generate,” on account of its forming water when burnt. It occurs in its free state in the bases of volcanoes, and by the aid of the spectroscope has been detected in the sun and stars. It chiefly exists in combination with oxygen as water, and is an important constituent of all vegetable and animal substances.
Hydrogen is obtained by the decomposition of water in various ways. On a large scale, nearly pure hydrogen may be prepared by passing steam over charcoal, or coke, heated to a dull redness. If the temperature be kept sufficiently low hydrogen and carbon dioxide will be the sole products, and the latter may be removed by causing it to traverse a vessel filled with slaked lime, but if the temperature be allowed to rise too high, or an excess of air be admitted, carbon monoxide is also produced, and cannot be removed from the mixture.
Pure hydrogen is a colorless, odorless, transparent and tasteless gas, and has never been liquefied. It is very slightly soluble in water. It is the lightest of all known bodies and is not poisonous, although it cannot support life, and if mixed with a certain proportion of oxygen it can be breathed for a considerable length of time without inconvenience. It is highly inflammable, and burns in the air with an almost colorless, nonluminous flame, forming water. A burning taper is extinguished when plunged into hydrogen, and all bodies which burn in the air are incapable of burning in hydrogen.
Hydrogen does not spontaneously enter into reaction with any of the elements, although it has a powerful affinity for several of them. Thus, when hydrogen and oxygen are mixed nothing occurs, but if a lighted splint is introduced a violent explosion ensues, water being produced. Similarly chlorine and hydrogen are without action upon each other in the dark, but if the mixture is exposed to a bright light, or if heated by the passage of an electric spark, the gases are at once combined with explosive violence, forming hydrochloric acid.
Hydrogen is usually prepared by the action of zinc or iron on a solution of hydrochloric or sulphuric acid. All metals which decompose water when heated readily furnish hydrogen, on treatment with hydrochloric or sulphuric acid. Many other metals enter more or less readily (although none so readily) into reaction with these acids. Also, many other acids than sulphuric or hydrochloric acids may be used, but none acts so quickly. In all cases the action consists of the displacement of the hydrogen of the acid by the metal employed, and if the acid is not one which can enter into reaction with the displaced hydrogen, the latter is also evolved as gas.
If pure gas is required it is necessary to employ pure zinc or iron, as the impurities in the ordinary metal communicate an extremely disagreeable odor to the gas.
The pure gas is not absolutely essential for lead burning, and owing to their being much cheaper, and also on account of their increased quickness of action, the commercial qualities of sulphuric acid and zinc are employed in the generator described.
The commercial zinc is known as spelter and is sold in pigs or blocks, which are easily broken into fragments, like stove coal, with a heavy hammer. The commercial sulphuric acid is known as oil of vitriol and is sold by the pound. The acid cannot be employed in its pure state, but must be reduced with water in the proportion of one part of acid to seven parts of warm water. They must be mixed by adding the acid slowly to the water; never the water to the acid. The combination of acid and water enters at once into reaction and always generates heat, and the result of adding water to acid would be small explosions. There would be danger of the acid flying on one's clothes or into the eyes. The mixture should never be stronger than six parts of water to one of acid.
The beginner will observe from the above that the generator cannot be crowded by making the acid solution strong. Hydrogen is a peculiar gas and also a dangerous one for one ignorant of its peculiarities to experiment with, and in order to thoroughly understand it the following experiments should be demonstrated, which can be done with little expense. The beginner should note the result of each experiment as demonstrated, and carefully commit the same to memory for future reference.