Autogenous soldering is accomplished by the fusion of the edges of the two metallic articles without the employment of another metallic alloy as a band of union. This is done by the direction of a jet of burning hydro-gas from a little movable beak, upon the two edges or surfaces which it is desired to solder together. There is less liability of metals thus joined cracking asunder at the line of union from strain, temperature, etc., than when the ordinary solder process is used. This system of soldering is quite advantageous in chemical establishments for joining the edges of sheet-zinc for concentrated pans and sulphuric acid chambers, as the speedy corrosion of soldering containing tin is inevitable.
When it is necessary to solder brass to cast-iron, the part of the iron to be soldered should be polished on an emery wheel until it becomes clean and bright. It should then be dipped in potash water, after which it is filtered for a moment in clean water and washed rapidly with ordinary undiluted hydro-chloric acid. It is then gone over with powdered resin and a solder made of 50 per cent. lead and 50 per cent. tin. This step must be taken before the surface drys.
(2) Another method is to file the surface clean, wash same and wipe it with a flux made by the dissolution of sheet-zinc in hydro-chloric acid until the latter is surcharged. That is. when it becomes a saturated solution and has been diluted with its own quantity of water. Then powdered sal-ammoniac is to be sprinkled on it and the mass is to be heated on a charcoal fire until the sal-ammoniac commences to smoke. It is then to be dipped in melted tin and on its removal the surplus tin is to be knocked off.
When it is desired to solder bright copper and to have the solder the same color as the copper surface, it may be done this way: Moisten the solder with a saturated solution of vitriol of copper and then, touching the solder with an iron or steel wire, a thin skin of copper is precipitated, which can be thickened by repeating the process several times.
To make the solder brass-colored, if it is desired to gild the soldered spot, it is first coated with copper in the manner indicated above, and then with gum or isinglass and powdered with bronze powder. The surface thus obtained may, after drying, be brightly polished.
To solder together cast-iron articles, first clean same and then brush with a scratch-brush until they are covered with a dry coat of brass, imparted by said brush. The surface thus covered with brass is then tinned just as brass itself is tinned and the parts are soldered as customary.
To make soldering fat, there should be melted in a pot over a hard coal fire 1 lb. tallow and 1 lb. olive oil, into which is stirred 8 ounces of pulverized colophony and the mass allowed to boil. After the mixture is cooled, add, with constant stirring, 1/4 pint of water which has been saturated with pulverized ammonia.