Soft Solder.—When two or more pieces of metal are joined together with a metallic cement, they are said to be soldered.

Sheet tin, of which cans are constructed, is always soldered with soft solder, a mixture of lead and tin, usually 50 per cent. lead and 50 per cent. tin.

This solder is usually supplied in wire or bar form at any hardware or electrical supply house.

Copper, brass, bronze, iron, silver, gold, and practically any metal except aluminum may be soldered with soft solder.

Sheet Tin.—Sheet tin, so-called, really consists of a thin sheet of iron coated on both sides with tin. This coating of tin serves several purposes. It enables the solder to adhere easily; it prevents the iron from rusting; and when the sheet tin is made up into can form, the tin coating protects the contents of the can from chemical action on the iron.

The Process of Soldering.—Soft solder is applied to the metal to be soldered in a molten state and this operation requires considerable heat. When heat is applied to metal it usually oxidizes that metal; that is, dirties it.

Solder will not adhere to oxidized metal. The metal must be protected with a coating called a flux while being soldered. Soldering paste, soldering fluid or “killed acid,” resin, paraffin, heavy oils, and vaseline all serve as fluxes, some better than others. The soldering paste is by far the best, as will be shown later.

Soft solder is applied to the tin, on the point of a hot soldering copper, often wrongly called a “soldering iron.” A soldering copper consists of a pointed bar of copper suitably fixed to an iron shank which is firmly set in a wooden handle. The point of the copper must be well coated with solder or “tinned,” so that when it is heated it will pick up the solder and convey it to the joint to be soldered.

The hot copper, charged with solder, is passed slowly along the joint and as the tin to be soldered receives enough heat from the copper, the solder leaves the copper and adheres to the tin, firmly uniting it.

Heating Apparatus.—Some form of heating apparatus is necessary to heat and maintain the soldering copper at the melting or flowing point of the solder. The copper may be heated in a gas furnace especially made for soldering coppers, or over an ordinary gas stove burner or a common blue flame oil stove, or a charcoal fire, a wood fire burned down to embers, or a plumbers’ gasoline torch, but never in a coal fire. Coal contains too much sulphur which oxidizes the copper and renders it useless for soldering purposes.

The Blue Flame Oil Stove.—For heating the coppers in my country shop, I use a blue flame oil stove, one of the less expensive sort, with the asbestos ring wick and the short removable chimneys. The stove has two burners and will heat from four to six coppers at once. The flames may be regulated nicely so as to give just the required amount of heat and this stove consumes very little kerosene, and, therefore, costs little to operate. In Fig. 16, it will be noticed that there is a curved hood over each stove hole. These hoods may be easily made from part of a large can or of a piece of tin or sheet iron bent into shape. These hoods conserve the heat and throw it about the coppers. I also place a piece of heavy wire netting over the grating of the stove holes to support the coppers and to permit their being laid to one side, out of the intense heat, when not immediately needed.

The blue flame oil stove forms the most satisfactory arrangement for heating coppers that I have ever used in the country. These stoves are easily taken care of and are understood by almost everyone. The directions should be nailed up alongside the stove and carefully followed, particularly as to cleaning the burners once or twice each season.

The Gasoline Torch.—The plumbers’ gasoline torch is often used by experienced metal workers for heating coppers. In inexperienced hands, this torch is rather a dangerous affair. Only one copper may be heated at a time and it is difficult not to overheat the copper in the fierce roaring flame. The cost of the torch and the cost of operating it are both greater than the blue flame kerosene stove. However, in experienced hands, it is safe enough and very useful about the shop. In using such a torch the directions should be most carefully followed; all joints, filler openings, etc., must be airtight when operating or a disastrous fire or explosion may result. The tiny jet opening in the burner must be kept clean.

The Gas Furnace.—In my winter shop in the city where gas is available, I use the gas furnace shown in Fig. 16. This is a most satisfactory and widely used heater for soldering coppers, as it gives an intense blue flame that may be easily regulated.

When using a heater of this sort, one must be sure that it is lighted correctly or a smoky yellow flame will result. To produce a blue flame, air must be mixed with the gas; just as it is in a bunsen burner or an ordinary gas stove, for that matter. Gas is admitted to the furnace through a small nozzle at the end of the mixing flue near the rubber hose connection. Air is admitted in the slot under the gas nozzle; a movable slide encircles the mixing flue over the slot to control the amount of air admitted. This slide must be tightly closed over the air vent when the gas is first turned on.

To light the heater, close the air inlet tightly, turn the gas on full and apply a lighted match to the burner. A yellow flame will result. Now open the air vent slowly, by pushing the slide forward a little way. The flame will change from yellow to blue and purple as air is admitted. When the flame is blue, it is giving out the most heat and is in the best condition to heat the copper.

If the flame fires back and lights the gas at the brass nozzle over the air inlet, the gas should be turned off until the flame disappears. The air inlet is then closed, and the gas turned on and lighted, and then the air inlet is slowly opened until the flame turns blue. When the furnace is in use, it should be looked at occasionally to see that the flame has not fired back to the nozzle. Once satisfactorily lighted, the heater may be turned up or down as needed. If the flame is turned down very low the air inlet may have to be closed a bit to prevent the flame from firing back. The copper is placed on the rest provided for it over the flame. After the copper is heated to the flowing point of solder, the flame may be turned down or the copper placed to one side of the flame, so that it does not get too hot.

Charcoal and Wood Fires.—When using a charcoal or a wood fire, the copper should be placed at the bottom among the embers. Small charcoal furnaces used for heating soldering coppers may be bought from the dealer in plumbers’ supplies. Charcoal should not be burned in a closed room as the fumes are deadly unless allowed plenty of constantly changing air. These furnaces may be connected with a chimney or burned in a room with windows opened, without danger.

A soldering copper may be heated in the glowing embers of a camp fire or in the embers in a fireplace.

Electrical Soldering Coppers.—The electrically heated copper is ideal for soldering as the heating coil is enclosed within the copper itself, the wire running out through the handle and connecting with an ordinary electric light socket. The heat is maintained at a proper degree for melting the solder; hence it is an ideal equipment for those who can afford it and where electric current is available. The doctors of certain hospitals have recommended electrical coppers for the use of patients in making tin can toys.

An electric soldering copper costs about $7.50 at the present time.

The Common Soldering Copper.—A suitable soldering copper or “iron” may be purchased at any good tool dealer’s or hardware store; it should weigh about one pound for work with the tin cans.

Almost everyone has purchased a small soldering outfit at one time or another and tried to solder the family wash-boiler or some leaky tinware; usually without success. Such outfits are invariably too small for large work or for the tin can toys.

It must be well remembered that the heat flows from the copper into the work, and that the copper has to heat up the work to the melting point of the solder; hence a large copper weighing several pounds is used to solder wash-boilers, tin roofs, etc., and a small copper weighing a few ounces is used for soldering jewelry, etc.

A large copper in expert hands may be used to solder very small work but a small copper may never be used to solder large work together, because the copper not only has to keep the solder melted to the flowing point, but also has to heat the work itself at the joint to the flowing point of the solder before the solder will leave the copper and adhere to the work.

In actual practice, it has been found that a copper weighing one pound is best. After one gets more adept with the copper, it will be found advantageous to have several coppers of different weights. A half pound and also a four ounce copper will be found very convenient for extremely small work. But, do not begin to solder with a copper weighing less than one pound.

Soldering coppers are usually sold in pairs at the large tool dealers, and coppers listed at two pounds really weigh one pound each; when sending in a written order be sure that you specify that the copper is to weigh one pound singly.

A wooden handle especially made for soldering coppers should be purchased at the same time as the copper; these wooden handles are made large to protect the hand from the heat of the iron shank. The handle is usually furnished with a hole of the proper size drilled in it to permit the pointed end of the shank to be driven in the handle easily with a wooden mallet. If the hole is too small, it should be drilled out so that it is nearly as large as the diameter of the shank. The wooden handle must not be split when driven on with the mallet.

Fluxes.—Before tinning the point of the copper, some flux must be obtained, either a soldering paste or soldering fluid “killed acid.”

An excellent soldering paste called “Nokorode” is by far the best flux obtainable. It is inexpensive, a little goes a long way, and it will not rust or corrode the work as is the case with killed acid and some soldering pastes. It may be easily cleaned from the work after soldering and it makes soldering much easier and simpler for the beginner. Nokorode soldering paste may be obtained at any good electrical supply house or hardware store. If they do not stock it, they will get it for you. There is nothing else just as good on the market, but if for any reason you cannot obtain this particular brand, be sure that any soldering paste you buy is plainly labelled that it will not corrode the work.

Soldering fluid or killed acid is made of muriatic acid in which is dissolved all the pure zinc that it will hold in solution. This fluid is much used by tinners and is certainly an excellent soldering flux, but not nearly as good as the soldering paste for our purposes. However, it is very useful in the shop to dip the tinned point of the hot copper into it to remove the oxide or dirt formed after the copper has been in use for some time. The solder will stick to the point much better after the copper has been cleaned in this manner.

Directions for making the killed acid and the use of other soldering fluxes will be found on page 68.

Tinning the Copper.—Having procured the soldering copper and handle, some flux and soft solder, and having fixed up some sort of heating apparatus, the next step toward soldering is to coat the point of the copper with solder: this is called tinning the copper.

Fix the copper firmly in a vise if one is at hand, as illustrated in Fig. 17. Then file each of the four faces of the point of the copper bright and clean with a flat file. It is better to use an old file for this purpose—one with rather coarse teeth. It will be observed that the copper is placed slantwise in the vise so as to bring one face of the square pyramid parallel with the vise jaws; this position permits filing in a natural horizontal position.

Each face of the point should be rounded slightly toward the point.

If a vise is not available, the copper may be held against the edge of the bench with one hand and the point filed clean and bright with the file held in the other, or a coarse sheet of emery cloth may be placed flat on the table and each face of the point rubbed bright on it. A file is by far the best for this purpose, however, and if it is chalked before using, the copper filed away will not clog it.

When the copper is clean and bright at the point each face should be thoroughly covered with a thin film of soldering paste or dipped into the soldering acid.

The copper should then be placed in the fire and heated to the melting point of the solder.

Heating.—While the copper is heating get ready a piece of tin about 2 by 4 inches—any clean flat scrap or part of a can will do. Spread a little soldering paste into the center of the tin and lay it on the bench near the heating apparatus. A few drops of killed acid may be placed on the tin instead of the paste, if the acid is to be used.

After a few minutes heating the copper should be removed from the fire and the end of a strip of solder touched to the point. If the solder melts quickly and easily against the point the copper is ready to tin; if it melts very slowly, “slushy”, the copper should be returned to the fire and heated a bit more. The copper should never be heated red hot under any circumstances; this must be borne in mind. If the copper is heated to a red heat, the soldering paste will be burned off and its action destroyed, for a red hot copper will not pick up solder, nor may it be tinned again until the copper is cool and refiled bright and clean, recoated with flux and reheated. If the copper is heated red hot after the point is tinned, the tinning is burned from the point and solder will not stick to it until it has been cooled, refiled and retinned.

This is the most important point to remember about soldering and is the cause of many failures. Remember that soldering is impossible without a flux to keep the metal clean when it is hot; too much heat will burn soldering paste or killed acid away; the tinning and the solder adhering to the point will be burned or oxidized and rendered brittle and useless.

A heat that will melt the solder almost instantly and cause it to flow with a brilliant glistening color should be maintained at all times when the copper is employed for soldering. This is never a red heat.

When the copper is first heated to be tinned, it should be removed from the fire when it melts the solder easily, and several large drops of solder should then be melted from the bar or strip of solder onto the piece of tin placed by the fire and on which some soldering paste or acid has been spread. Rub each face of the point of the copper into the solder on the tin until each face is thoroughly covered with a bright coating of solder. Hold each face flatly down against the solder on the tin during the rubbing process. The copper may have to be heated once or twice by the beginner, as it may get too cool to melt the solder easily. As soon as the solder begins to work stiffly, “slushy,” and looks gray instead of glistening, it is time to reheat the copper.

An old piece of soft cotton cloth, such as a stocking, on which is sprinkled a little powdered sal-ammoniac is an excellent thing to keep handy when soldering or tinning. The tin coating of the point of the copper should be rubbed on this cloth where the sal-ammoniac is sprinkled, when the copper is hot. This will be found to keep the copper in excellent condition. The sal-ammoniac removes the oxide from the tinning and brightens it up generally about the point.

The tinning will last much longer on the copper if it is dipped occasionally into the soldering paste or acid while hot. This is particularly true if the copper has been a bit overheated.

When the tinning shows signs of wearing off and the copper does not pick up solder readily, it must be retinned, filed, fluxed, heated, and rubbed on the solder which has been put on the tin first used for this purpose. This piece of tin should be kept about the bench, as the copper will have to be retinned frequently. Always remember that the copper will not carry solder to the work unless it is well tinned.

If an electrical soldering copper is used it is usually furnished already tinned at the point, so that it is ready for use as soon as it is connected to a suitable electric socket and the current turned on. The heating coil inside the copper will soon heat it up to the melting point of the solder. After heating, it may be treated as a common copper, wiped occasionally on the cotton cloth and retinned when the tinning is worn away. An electrical copper should never be placed in a vise for filing, but should be held against the bench and filed carefully. A vise is apt to crush the hollow copper and injure the heating coil inside. These coppers should never be placed in a fire or heated in any way except by the electric current.

Electrical coppers do not need as much attention as an ordinary copper for the even heat supplied by the current keeps the copper heated to the flowing point of the solder and is incapable of heating beyond this temperature.

How to Make Soldering Fluid or “Killed Acid”

Soldering fluid may be very simply made as follows: Pure zinc is dissolved in muriatic acid until the acid will not dissolve any more of the zinc. The solution thus obtained is then allowed to stand for a time and is then strained through a cloth and poured into a bottle which is kept tightly corked when not in use.

First purchase about six ounces of muriatic acid from a druggist. Take care not to spill any of this acid on the hands or clothes. Next get some pure sheet zinc. The sheet zinc employed for stove mats as it is sold in the plumbers’ shops is not suitable for making soldering fluid, as this form of zinc is alloyed with other metals. Pure zinc may be very easily obtained from old dry batteries which may be found anywhere.

Remove the paper covering from the battery and crack it open with a hammer—remove the carbon from the center of the battery and dump out all the powdered material. Soak the zinc covering of the battery in warm water to remove any paper or material adhering to the zinc and then cut the zinc into pieces about ¼ inch square.

Find an old tea cup or earthen-ware marmalade jar and pour into it about half a teacupful of the muriatic acid. Set the vessel containing the acid out of doors or near an open window and away from all steel tools, so that the fumes of the acid may escape and not be breathed into the lungs or rust any tools.

Pour a small handful of the zinc cuttings into the acid. The acid will attack them at once and a strong bubbling action will result. When the bubbling action dies down add more zinc cuttings—about every fifteen minutes. When the acid shows no sign of attacking the zinc as it is added, the acid is said to be “killed” and the soldering fluid is made. It may be used at once if necessary, but it will be much better if it is allowed to stand over night with the zinc residue left in it. It is then strained through a piece of muslin cloth into another cup or jar and the fluid is ready for use.

Soldering fluid may be kept in a wide-mouthed glass bottle or a marmalade jar; either vessel must be tightly corked when not in use. This soldering fluid may be used as a flux for any soft soldering operation in place of the soldering paste, but it is not as satisfactory a flux for the tin can work as the paste. The best use for it in connection with the tin can toys is to keep it to dip the point of the hot copper in occasionally to clean the tinning at the point of the copper.

While the prepared soldering paste is best for all soldering operations connected with the tin work, other fluxes may be used if nothing better is at hand. These are resin, olive oil, cottonseed oil, automobile lubricating oil, and paraffin; but these fluxes are not very satisfactory in inexperienced hands. The soldering paste is best for all soldering operations.