The problems involved in considering substitutes for things which are the result of life processes are even more complex. Citing clothing as an example, changes in human habits and con siderations of style are extremely important. Only a few years ago wool and cotton were the principal materials from which arti cles of clothing were made, but in recent years demands have been transferred so largely to silk and fur that the woollen and cotton textile industries have been seriously affected. Straw, ribbon and other materials were formerly used extensively in making women's hats, but now felt hats are almost universal. To what extent de mands for materials may be affected by a change in styles which may be brought about by skilful advertising and merchandising is exceedingly difficult to prophesy. Such changes have some limits imposed by physical conditions; thus wool is used for men's outer garments, because they keep their shape better.
In food products the tendency has been steadily to increase the number, variety and quality over a long period of years, with the result that people are now better nourished than at any previous period in human history. Fruit, for example, instead of being available to only the wealthier class outside the growing season is now a regular article of diet in almost every home all the year round ; its greater consumption, it is believed, has led to a decline in the per capita consumption of meat. Sugar and chocolate are also used much more extensively than formerly; these, like most other food products, seem capable of being pro duced in any amounts that are required. Chewing gum, though not a food, is, however, an example of an organic product for which it may be necessary to find a substitute, as its increasing use bids fair to outstrip the present supply of chicle gum (the principal ingredient), which is the only gum that at the tem perature of the mouth is neither too soft nor too hard, and is also free from any objectionable flavour. Rubber illustrates the
manner in which public concern over supply of raw materials varies. The demand for rubber was easily met, until the introduc tion of the automobile forecast a great increase. This caused much concern for future supply and many chemists have worked to discover substitutes. The great increase in rubber production in Malaya shifted attention to schemes to maintain the price of the raw material in the face of production that had increased faster than consumption. If anything equally serviceable can be produced and sold at less cost it will be adopted, but the world can produce what is needed without necessity for any substitutes. Raw material for paper manufacture has long been a source of concern. Different materials are used to produce the various grades of paper, but newsprint, which is the largest in demand, is made from wood pulp. For the purpose soft woods are re quired, and these woods are also the principal kind needed for lumber purposes. Neither newsprint nor lumber has much sal vage value and they are largely destroyed by their first use. Some progress has been made in decreasing the demands on lumber for packages, and it has also been found possible to remove the ink from newspapers, though not sufficiently to permit the re-use of the stock for the same purpose. It seems probable that wood and all the other raw materials that are produced as a result of growth can, with care, always be produced in sufficient amounts to meet human needs, so that the problem is really one of pro ducing them at a cost which will not produce some economic shift that disturbs the complex equilibrium in modern industry. Shifts of this sort result from so many other causes in addition to shortage of essential raw materials and human ingenuity has been so successful in meeting them thus far that while the study of substitutes is proper for the engineer and chemist, it does not at present need to be a matter of great public concern.
(T. T. R.)