Tin-plate, in addition to being used for cans, is utilized for roofing purposes; obviously glass could not be so used. Terne plate (an alloy of lead and tin) is, however, used for roofing, but could not be used for food containers as the lead in the alloy pro duces toxic effects. Collapsible tubes made of tin are extensively used as containers for tooth-paste, shaving cream and various other commodities of a creamy consistence; no satisfactory sub stitute for tin has been devised for this purpose. Tin foil is used as a wrapping for candy and chewing gum, as a lining for boxes and cartons of cigarettes and for a variety of other purposes. Aluminium foil and lead foil are, to a growing extent, substitutes for this use, but neither has the bright lustre of tin foil. Except for appearance, paraffined paper would serve this use equally well. A variety of attractive transparent, moisture-proof and dust-proof wrapping materials have been placed on the market recently and, for some purposes, they are much better than tin foil, while for other uses they are inferior. Tin when alloyed with copper produces bronze, which has a variety of uses that it best serves. For some of these uses silicon or manganese can be used as the addition agent to the copper, but for others they are not satisfactory. When manufactured for transmission wire, cadmium can be used, with better results than other substances from the transmission standpoint, although not from other con siderations. Tin is also used in. the alloys employed for bearings in machinery. These alloys are of great variety, depending on the service required of them, and a discussion of possible substi tutes would be exceedingly complex. Tin has a variety of chemi cal uses, two of the most important being for making enamels and weighting silk. In both cases the use of substitutes is possible.
For tin, therefore, various things may be used as substitutes in its various uses, with variable degrees of effectiveness, accord ing to the circumstances of each case. No one can safely prophesy that research will not reveal some substitute that will give equally good service at equal or even less cost and, on the other hand, no one can safely prophesy that it will. The whole subject of substitutes is charged with uncertainty from its very nature. In the search for substitutes several general considerations must be maintained as objectives. The first is that the substitute should be more abundant than that which it replaces ; little advantage is gained if a sufficient supply of the substitute material is not available. A second is that the substitution should be real, not fictitious; large quantities of power or of other materials should not be generally involved in making the substitution. Substitutes should, if possible, be locally available, to avoid the burden of transportation cost, and also to avoid the possibility of being de pendent on foreign countries for a source of supply. Finally, the
substitute should not impose too heavy a task in changing the habits of consumers, or the usual processes of plant operations.
The principal use of manganese is in connection with steel manufacture and for this purpose an alloy containing 8o% man ganese is usually employed. In America manganese ore of the desired quality has to be imported; domestic ores can be used to make a 20% alloy but less conveniently, as the 20% alloy has to be added while molten, although solid lumps of the 8o% alloy that can be employed are commonly used. Substitution of the lower grade alloy is made difficult by this consideration.
Substitutes for gasolene have been much discussed and alcohol is one of the various materials that have been proposed. It has the great advantage that it can be made from vegetable mate rials that are reproducible. Alcohol cannot, however, be used ef fectively in an engine built to use gasolene; it needs one specially designed for it. Its general use as a substitute would therefore involve not only the organizing of industry to produce and dis tribute the alcohol, but also the replacement of over 20,000,000 gasolene engines. Another possible substitute is gasolene made from oil shale. To mine the shale required to produce any con siderable part of the gasolene now used would require the setting up of a mining industry of approximately the same size as our present coal-mining industry, and this industry would have to be in regions that are now very sparsely inhabited because they are arid. Thus not only a shifting of population would be required, but also the provision for water and food supply, housing and other facilities. The task is thus much more complex than the working out of a process whereby gasolene can be made from oil shale.
Substitution of one product for another not only involves the various considerations outlined above, but often requires the finding of adequate markets for by-products. Much has been said about the wastefulness of buying coal in its raw state, and one of the principal subjects for research is the processing of coal to yield coke, gas and a great variety of by-products. The propor tions of these various things that can be made are definitely fixed by chemical and engineering considerations, but the markets for them are quite variable, not only from day to day, but over longer periods. The demand for gas may be greater than the demand for the coke produced, or it may be less, and these relations may shift from day to day or week to week. For a time it was difficult to find adequate outlet for the benzol made as a by-product, and it was chiefly used as a substitute for gasolene. However, develop ment of the nitro-cellulose lacquers provided a large demand for benzol at an increased price, and the present supply was in 1929 practically all used for this purpose.