This section is from the book "Amateur Work Magazine Vol6". Also available from Amazon: Amateur Work.
Two properties render magnesium a valuable metal: First, its lightness. It has even a less specific gravity than aluminum. Second, its affinity for oxygen. This fact renders it of great value in deoxidizing other metals.
Magnesium is made in the same manner as aluminum by means of the electric furnace. Chloride of magnesium is produced. The discovery of magnesium is due to Sir Humphey Davy, but Bussy, in 1830, first obtained it in the coherent condition. The price was then very high and it is only recently that the price has been reduced so that it can be economically used in the arts. Only a few years ago the price wa6 over $5.00 per pound.
Magnesium belongs to the zinc family of metals. Zinc, cadmium, magnesium, and beryllium constitute this group, as they are quite similar in their properties. For example, magnesium burns in the air like zinc, and with the formation of the oxide.
In color magnesium is much whiter than aluminum and has more of a silvery lustre. The specific gravity of aluminum is 2.56 and magnesium is 1.75. It will be seen, therefore, that magnesium is much lighter than aluminum. This very fact renders magnesium of much value in the manufacture of aluminum and magnesium alloys. Such alloys are lighter than aluminum, and are strong and stiff. There is no other metal that can be added to aluminum to harden it except magnesinm which will not increase its specific gravity.
For light alloys, magnesium opens up an entirely new field, and as alloys, lighter than aluminum and equalling brass in strength, can be made from a mixture of aluminum and magnesium, many new uses will be found for them.
The fact that magnesium has more affinity for oxygen than any other metal renders it the strongest de-oxident. It is the only deoxidizing agent that will decompose carbon monoxide when it is present in a melted metal. It entirely eliminates all gases from a molten metal, therefore, and sound castings result. In this direction it will accomplish results impossible with other deoxidizing agents.
Magnesium has such an enormous affinity for oxygen that when in a finely divided condition, it will burn with the formation of an intense light. This property has brought about its use in flash light powders used in photography.
A popular belief exists that, inasmuch as magnesium in the form of powder will burn, that large masses will likewise burn easily. This is not so and a large mass of magnesium, such as the commercial sticks cannot be made to burn any more than zinc un-. dersimilar condition. It is only the finely divided material that is combustible. In a flash light powder it is not the magnesium itself that is explosive, but the mixture of the magnesium powder and chlorate of potash. Magnesium itself, either in powder or masses, is not dangerous to use.
Heretofore, many failures in the use of magnesium occurred on account of the impurity of the commercial magnesium that was on the market. Much of the magnesium contained sodium, silicon, and other impurities, which interfered with some of its uses. It is possible at the present time, however, to obtain magnesium of great purity and in an easy form to use. It is now sold in the shape of sticks about half an inch square and a foot long. These sticks have been sawed out of a solid block and are very covenient to use.
The difficulty which has been experienced heretofore in using magnesium as a deoxidant has been in the use of too great a quantity. Only enough should be added to reduce the oxide and gases that are present. The addition of several per cent, of magnesium as frequently recommended, is not conducive to good results. The large excess of magnesium in copper, for example, renders the casting dirty. The quantity of magnesium to be added is usually about 2 oz. of magnesium to 100 pounds of metal. Frequently less will do the work and give better castings. - " The Brass World."