This section is from the book "Soldering For Workshop, Farm And Home", by John Bonert. Also available from Amazon: Soldering For Workshop, Farm And Home - Information On Soft And Hard Soldering - Projects For The Workshop Explained And Illustrated.
The beginner should have some knowledge of the common metals used in soldering and metals which can be soldered. This will help him to a great extent as some metals that can be soldered melt at a low temperature. Solder is a composition of metals which melt at a lower temperature than the metals to be united. The following are approximate melting temperatures of metals which will concern the beginner.
Melts at, 420
" " 615
" " 775
One part tin-one part lead
" " 390
One part tin-two parts lead
" " 400
Two parts tin-two parts lead and one part bismuth
" " 290
It will be seen that the composition of half lead and half tin which is the solder most commonly used will melt at a lower temperature than either lead or tin separately. The Chemical Dictionary gives the definition of solder as, "an alloy consisting of two or more metals having a melting point below that of any of the metals that make up the composition and used for joining other metals together by soldering, brazing or welding." Some solder is composed of 60% lead and 40% tin, but the best solder for general work is called "half and half" which is 50% lead and 50% tin. It is false economy to use solder with less than 50% tin because solder that is rich in tin will flow and sweat more freely than solders containing less tin. If solder contains more than 50% lead it can be detected easily. Melt a few drops of solder with the hot soldering copper, about the size of a dime, on the surface of an ordinary building brick. When these drops cool, if the solder is half and half the surface will appear bright all over. If the solder contains more than 50% lead, only some of the surface will be bright. Part of the surface will have a chalky appearance. Solder may be purchased in a number of forms. Bars weighing about one pound each, solid wire in thicknesses from 3/32" to 1/8", wire with a core of rosin and wire with a core of acid flux.
Tin is a white metal the color of silver. At this time it might be well to explain that many people have the mistaken idea that ordinary cans used as containers for vegetables and meats are made of tin. These are really only "tinned" cans. They are made of sheet iron or sheet steel covered with a coating of tin. If the so-called tin can is placed in the fire this coating of tin burns up and only the iron or steel is left just as a soldering copper which has become red hot will lose its tinning.
Tin is used for many purposes such as tinfoil, tin squids used on fish hooks, and pipes used at beverage fountains. It is used for tinning copper and iron cooking utensils. It is used in composition with other metals to make bronze and Babbit metal. Cooking utensils that are tinned should never be placed on the fire without some liquid in them as the tinning would be burned off. Tin takes a very bright polish.
Tin is a very difficult metal to solder on account of its low melting temperature. A special solder is required which is called, "Woods metal." This is a composition of lead, tin and bismuth. There would be a very small margin between the melting point of half and half solder and the melting point of tin. If one tried to solder tin with half and half solder the heat required to bring the solder to the proper temperature would surely melt the tin and ruin the work. By adding bismuth to the solder the melting point is lowered to about 290 degrees, Fahrenheit. The soldering copper cannot be as hot as for other metals.
Lead is known and recognized by most craftsmen and does not need much explaining. It has a blue silver color and is quite bright when the surface is newly cleaned or cut. It turns a dull gray after long exposure to the air. It was one of the most used metals when all plumbing was lead but very little is used in plumbing today. Iron, brass and copper have taken its place. Sheet lead is still used very extensively for acid containers, roof flashings, trays for acid overflows and many other purposes. Storage battery plates are made of lead. The covering for telephone and electric wires known as cables is made with a small percentage of antimony in the lead. Antimony is a white metal similar to tin. It is used as a hardening ingredient. Lead is one of the easiest metals to solder if certain precautions are taken which will be fully explained further on in the lessons. Lead can be worked to most any shape by bending and hammering as it is very malleable.
Zinc is used a great deal in sheet form. It is used for lining some forms of ice boxes such as fish are displayed in at fish stores, to cover counters where water and ice are used. It does not corrode. Galvanized iron is coated with zinc to retard corrosion. Zinc is used as a casing for dry-cell batteries and for the negative element of sal-ammoniac batteries. The most important use for zinc is in composition with other metals. Zinc tins very easy but as it melts at quite a low temperature great care must be taken not to melt it when soldering.