After many years of experience, we have developed the following method of manufacture. The lead is first melted at a temperature which does not cause too rapid fusion. After the dross has had a chance to rise to the surface, it is carefullv skimmed off before the required amount of tin is added, and slowly reduced to the liquid state. From the moment the tin is added, the solder is stirred by hand for 3 hours to 4 hours. A scavenger is then added and thoroughly worked for another 3 hours to 4 hours ; the resulting dross is again skimmed, and the solder is cast into pigs of approximately 80 lb. each. These pigs are then re-melted in smaller kettles at a temperature which just causes free fluidity, and the solder is then cast into the desired shapes. During the entire operation of final casting, the caster stirs every time he takes a ladlefu! from the pot.

This work could be done much more rapidly at higher temperatures, and much more economically by the use of mechanical mixers, but the resulting solder would not be so thoroughly mixed, nor would it be so fluid. Mechanical mixing has a tendency to drive the oxide and dross back into the metals, thus diminishing the holding power of the solder. The scavenger must be chosen with great care, and the amount must be very accurately gauged ; otherwise the scavenger becomes a constituent of the finished product, and, instead of being beneficial, is a detriment. We have found that in the grades of solder containing 46 per cent, and less of tin, the addition of 1/2 per cent, to 3/4 per cent, of the best grades of antimony increases the fluidity and holding strength of the solder for working tin plate.

Next to its use for containers the largest consumption of solder has been on gasolene motor radiators. The hand work on these radiators requires merely a free-flowing clean solder, but on the dipping work where most of the solder is used, the greatest abuse has been practised. As these radiators are composed of copper low brass, or ordinary brass, no antimony whatever should be added to the solder used for this purpose. Also the affinity of tin and lead for zinc and copper will draw both of these metals from the radiators into the baths, and as both copper and zinc make solder sluggish, it does not take long (unless proper methods are employed for cleansing the baths) for the solder to become deteriorated.

These baths can be thoroughly cleaned by a mixture of rosin and sulphur, but as this operation produces very disagreeable black smoke throughout the plant, some method should be devised for disposing of it. When sulphur is used for removing zinc and copper, a sufficiently high temperature should be employed to insure the complete combustion of the sulphur. The baths should then be allowed to settie for at least half an hour after such heating, and the top carefully skimmed to remove any sulphides present. It is important to note that the presence of any non-metallic substance is injurious to solder, whether it has been added as a scavenger or is liberated from the original metals.

The question is frequently asked, what is the strongest solder that can be made ? Numerous experiments have been made, but the results are confusing. Tests of tensile strength, based upon wires and cast bars, indicate that the higher the tin, up to 75 per cent, tin, 25 per cent, lead, the greater the breaking strength ; in the case of two pieces of tin plate soldered together, the maximum strength is given by a solder containing around 42 per cent. tin. Other tests were made on square 5-gallon cans, completely filled with water and then capped; when dropped from a height of about 100 ft., the cans soldered with 46 per cent. tin. 54 per cent, lead, in no case broke at the seams, although the tin plate was ruptured. This was the only mixture that gave this result. Cans soldered with 47 per cent, or more of tin, 53 per cent, or less ot lead, and with 45 per cent, or less of tin, 55 per cent, or more of lead, occasionally ruptured at the seams. These experiments were made most carefully and were afterwards confirmed by subjecting the cans to air pressure.

I am thus inclined to believe that, in round figures, 46 per cent, tin, 54 per cent, lead, is the strongest mixture than can be used for general soldering purposes, particularly if 1/4 per cent, to 1/2 per cent, of antimony be added to the mixture. The Bureau of Standards, with the approval of the War Industries Board, suggests that the highest grade of solder permitted should be 45 per cent, tin, 55 per cent. lead. For mechanical soldering, 40 per cent, should be the highest tin ratio, and for most bath work it has been demonstrated that tin from 35 per cent, to 38 per cent., according to the nature of the work, will give ample satisfaction, provided the solder is made properly. (Engineering.)

A Useful Solder

Copper dust is prepared by precipitation of a sulphate of copper solution by using zinc in a suitable crucible and mixing with strong sulphuric acid. Use 30 parts of the copper dust, and add 70 parts of mercury, stir well while adding. Wash the amalgam well with warm water, and allow to cool. When required for use, heat it well and pound in a crucible until it becomes as soft as wax, then spread it over the surfaces to be united, when cold and hard it is very effective.

Soldering Small Articles

It is sometimes very difficult to solder very small articles together without disturbing their position. The binding together with ordinary wire etc. is not satisfactory, as this wire gets soldered also, but if fine aluminium wire be used the trouble disappears, as the aluminium will not take the solder. The objection that may be raised is that such wire is seldom to hand when required, but generally there can be found either a sheet of thin aluminium, or a tube, pot, or vessel from which a very narrow strip can be cut wilh a pair of ordinary scissors, making a very efficient substitute for a wire, and for some operations it is even better. To Solder Small Delicate Articles.

-Bury the part not required to be got at while soldering, in a small box of wet sand, or cut a juicy potato in halves and place the portion of the article between the two halves, tie the two halves together in some convenient way.