Fig. 463.-Forms of Soldering Coppers and How to Tin Them.

vent it from flowing freely. The metal at the seam is heated by a very hot bit or the flame from a blowpipe so that there is a uniform flow of lead across the seam. It is sometimes necessary to add more lead to the seam by melting a strip held in the hand. A flame of some sort is the most satisfactory source of heat for the average lead burning job, because not only is the heat more uniform, but also more intense, and the lead melts at the desired point before the surrounding metal becomes sufficiently hot to soften. There are several types of blowpipe for this purpose on the market. Some employ an alcohol flame, while others make use of mixed hydrogen and air. The flame is usually small, sharp-pointed, and

very intense. Lead burning is absolutely necessary, and is insisted upon in certain classes of work for instance, in lining tanks with lead for chemical solutions, or for joining the grids and lugs of storage batteries.

Soldering Aluminum.-Many components of the modern motor car are made of aluminum and in making repairs, if these be broken or cracked, this metal is extremely difficult to solder. While many attempts have been made to solder aluminum in the ordinary way, and even with special fluxes and solders, but little success is obtained unless the conditions obtaining are fully appreciated. Aluminum is very light and melts at comparatively low temperatures, and because of its rapid oxidization it is necessary to take great care to secure bright metal to which the solder will adhere. The alloys with which the motorist has to deal vary in proportion of alloying elements, depending upon the use for which the metal is intended the substance commonly used in combination being zinc, copper, tin, manganese, magnesium and sometimes a trace of iron. The larger proportion of any alloy is aluminum, and on the whole the soldering problem will be about the same in all cases. As must be obvious because of its low melting point, aluminum will not stand prolonged heating, a condition that may be disregarded in the case of most of the other metals amenable to soldering and brazing processes. Then again, when the critical point is reached in the heating, aluminum suddenly "wilts" and every precaution must be observed to prevent the metal becoming too hot. The following table will show the relative 'melting points of the common metals:

From the foregoing it will be evident that the metals of which the average solders are composed have melting points but little lower than that of aluminum, and careful manipulation will be necessary to insure heating the metal sufficiently to melt the solder, and at the same time not weaken the aluminum or cause it to flow. To successfully solder aluminum demands considerable preparation and careful manipulation, and authorities differ as to the best methods and solders to use. All agree that the metal must be dry and absolutely clean, and while this is easily said and advised it is difficult of accomplishment. If one cleans aluminum in ordinary temperatures, no matter how carefully, and obtains a bright surface, it is impossible to retain this as new oxide forms on its surface as soon as brightened. For this reason, some skilled in the arts recommend immersing the parts to be soldered in a strong solution of hydrosulphate of soda for several hours before joining them. The best solder to be used depends to a certain extent upon the alloy of aluminum, the same as with other metals. One that has been used with good success is made as follows: Ten parts each by weight of tin, cadmium and zinc and one part of lead all of which are melted together.

Dampness or salt air are the bane of the process of aluminum soldering and the rapid oxidization makes "tinning" which is of such benefit in uniting other metals, practically impossible. As moisture will hasten oxidization, the safest method of proceeding will include the drying of the surfaces, assuming that these have been properly prepared, as well as the solder, in an oven or other suitable container at a high enough temperature to thoroughly heat all parts, but lower than that required to melt the solder. When the parts are thoroughly dry, the next thing to do is to scratch the surfaces vigorously with a metal brush, bringing out the un

tarnished metal, and removing all traces of oxide. The next step is the heating of the aluminum parts nearly to the melting point of the solder, and after applying the alloy to the surfaces, brush it into intimate relation with the surfaces, using the metal brush. If the solder does not adhere there is still some oxide on the surface, and the operation of cleaning should be repeated. When the surfaces to be joined are properly coated with solder, the rules which govern ordinary soldering work will apply, it being merely necessary to heat the surfaces, melt the solder and join the surfaces. Either a bunsen burner or blow torch can be used to heat the metal, and the important points to remember are that the work must be done quickly and that the surfaces to be joined be as clean and dry as possible, and as free from aluminum oxide as conditions will permit.

If the surface is of such a shape that it cannot be readily cleaned by scraping, it can be cleaned by dipping it into a solution of nitric acid in three times its bulk of hot water containing about 5 per cent. of commercial hydrofluoric acid. This causes a slight aetion on the surface of the metal as shown by bubbles. Rinse the metal after removing from the acid bath and dry in hot sawdust. There are various compounds on the market for soldering aluminum, but this operation depends more on the workman than on the solder and unless considerable experience has been had it is probably better to purchase solder than attempt making it. Zine can be used but does not form a very strong joint. Tin can also be used; is more nearly the color of aluminum, is stronger than zine, but is very difficult to work. A small proportion of phosphor tin added to pure tin makes it work more readily and is the basis of most aluminum solders. The chief difficulty in soldering aluminum is that the heat is dissipated so rapidly that it cools the soldering iron and furthermore aluminum oxidizes instantly upon exposure to the air. This extremely thin film effectually prevents a perfect union being made. If the parts are well heated and melted solder kept hot while the iron is allowed to stand on it, the surface can be scraped beneath the melted solder by the point of the soldering iron, thus preventing to a certain extent the oxidization. In this way the metal can be tinned. When both parts are brought to

gether and are well tinned, they can be united with some chance of success, nitrate of silver, resin, or zinc chloride being used as a flux. A soldering tool of nickel gives more satisfactory results than a copper one as the latter alloys with the tin and soon becomes rough.

Another authority advises as follows: Use zinc and Venetian turpentine for soldering small surfaces. Place the solder on the metal and heat very gently with a blowpipe until entirely melted. Another is to clean the surfaces by scraping and covering with a layer of paraffine wax as a flux then coating the surfaces by fusion, using a layer of alloy of zinc, tin and lead, preferably in the following proportions: Zinc, five parts; tin, two parts; and lead one part. Metallic surfaces thus prepared can be soldered by means of zinc or cadmium, or alloys of aluminum with these metals. Twenty-eight ounces of block tin, three and one-half ounces of lead, seven ounces of spelter, and fourteen ounces of phosphor tin, containing 10 per cent. of phosphorus, will make a good aluminum solder. Clean off all dirt and grease with benzine, apply the solder with a copper bit, and when the molten solder covers the metal, scratch through the solder with a wire scratch brush. A good solder for low grade work is composed of tin, 95 parts, and bismuth, five parts. A good flux in all cases is either stearin, vaseline, paraffine, copaiva balsam or benzine. Small tools made of aluminum or nickel should be used in the operation of soldering. These facilitate at the same time the fusion of the solder and its adhesion to the previously prepared surfaces. Copper or brass tools should be avoided as they would form colored alloys with the aluminum and the solder. To sweat aluminum to other metals, first coat the aluminum surface with a layer of zine, on top of which is melted a layer of alloy of one part aluminum to two and one-half parts of zinc. The surfaces are then placed together and heated until the alloy between them is liquefied.

How to Braze Steel and Iron.-As with soldering, it is important in brazing to clean the work thoroughly. Sand blasting is an ideal method of cleaning for brazing, although the work may be done with a file and emery cloth. The sand blast not only cleans the metal of all scale, but penetrates the pores, leaving it in condi