We observed in the chapter on “Roofs,” that within the last few years, the metal zinc has been much used instead of lead for all the purposes of the latter, and many others beside, for which the admirable qualities of zinc particularly qualify it. This metal is lighter than lead, and equally durable in the open air. It bears water almost equally well; but it is not so flexible or manageable, being neither so fusible nor malleable. Zinc only admits of being rolled or hammered when it is heated to about two hundred and twenty degrees of Fahrenheit. When cold it is too brittle to bear much bending; nevertheless, pipes, gutters, cisterns, chimney-pots, &c., are made out of sheet zinc; and roofs, &c. covered with it.
Solder or Cement for Metals.
The solder alluded to above, as being the means of joining two pieces of sheet lead or of lead pipe, is an alloy of lead and tin, in the proportion of two parts of the former to one of the latter. This mixed metal is fusible at a lower temperature than either the tin or the lead separately; and may therefore be applied in a melting state to tin or lead, which still remains solid, even at the same temperature: this it is which constitutes the principle of soldering. The solder is cast into triangular bars, weighing from thirty to fifty pounds each.
There has, however, been a method recently introduced which seems likely to effect considerable changes in the mode of joining pieces of metal, whether for buildings or for other purposes; and we may here give some account of it.
The great object of soldering is of course to form joints or seams in pipes, and other articles, so perfectly, that they shall be subject to no leakage or flaw. But this object is not easily obtained by the old method of soldering; the chances of flaw are numerous, and have been enumerated thus:—1st, the difference of expansion between the lead and its alloys with tin, a difference which is particularly experienced in very cold or very elevated temperatures; 2nd, the electro-chemical actions which are developed under certain circumstances by the contact of two different metallic substances;[5] 3rd, the very powerful reaction which a number of chemical agents exert on alloys of lead and tin, though not upon lead alone; 4th, the extreme fragility of these alloys, which, particularly when heated, often break on the slightest blow; 5th, the difficulty of making the solder adhere to the surface of the lead;[6] 6th, the use of rosin, which frequently conceals fractures for a time.
All of these objections are removed by a new method of soldering, invented by M. E. Desbassays de Richemont, who has recently obtained, at the National Exhibition of Arts at Paris, a gold medal for his invention. The committee on whose recommendation the medal was awarded, included some of the most distinguished chemists and men of science in France; and in their report on the subject, they say:—“We consider this invention of the highest importance; it is applicable to many branches of industry, and will render great service to a large number of manufactures. Its efficacy has not only been proved by experiment, but is confirmed by the fact, that most of our eminent manufacturers and tradesmen have taken out licences for the use of it.”
This invention (which is patented in France, Great Britain, and Ireland) is called autogenous soldering, and consists of a method of uniting two pieces of metal without the use of solder. The parts to be joined are united by the fusion of the metal at the points or lines of junction; so that the pieces when joined form one homogeneous mass, no part of which can be distinguished from the rest. This result is obtained by means of jets of flame, produced by the combustion of hydrogen gas, mixed with atmospheric air; these jets are so ingeniously managed, that they can be used and directed with as much, or even more facility, than the common tools of the solderer.
The apparatus employed in this new process consists of a peculiarly constructed vessel for producing hydrogen gas, to which vessel a variety of tubes and jets can be attached, so as to meet the various demands of the solderer.
A section of the gas-producer is shown in fig. 1: a is a leaden tank, for containing dilute sulphuric acid; b, a pipe which passes from the acid vessel to another similar leaden vessel, c, which is to contain cuttings of zinc; d is a conical plug, with a stalk and handle covered with lead, by the opening of which the acid is allowed to flow through the pipe b, to the zinc cuttings, and thus hydrogen gas is produced; e is an opening by which zinc is put into the vessel c. The opening, e, has a cover furnished with screws and nuts, by which it may be firmly secured; f is an opening by which acid and water are poured into the vessel a. When the hydrogen gas is produced, it has to pass through the safety chamber g; h is a bent tube or pipe, which conducts the gas from the vessel c to the bottom of the safety chamber, the mouth of the pipe dipping into an inch or two of water in the safety chamber. This water is introduced by the pipe i, which is furnished with a stopple. The cock, k, cuts off the flow of gas from the vessel c, to the safety chamber, g. A flexible tube, m, is screwed to the top of the safety chamber, and conveys the gas to the working instrument, or jet, in the hands of the solderer.
As long as the dilute acid is allowed to flow upon the zinc, hydrogen gas will be produced: the gas will also be formed as long as the cock is open, which allows the gas to issue as it is produced; but as soon as the cock is shut, a small quantity of gas accumulates, and interferes with the further action of the liquid on the zinc. Consequently there is no danger of an explosion, because the production of the gas is never more than is required for working; and when the work ceases, the production of the gas ceases also. When the dilute acid has become saturated with oxide of zinc, and gas ceases to be produced, the discharging pipe is opened, and the liquid withdrawn. By spontaneous evaporation, this liquid furnishes sulphate of zinc (white vitriol), which may be sold at a price which will more than cover the first and daily cost of the apparatus.