These facts show that the lead resources of the United States will be drawn on heavily in the future. The production of the United States increased from about 70,000 tons in 1880 to 365,000 tons seventeen years later, and if continued the yearly production by 1920 will amount to 580,000 tons, or more than a billion pounds.

The princ.i.p.al lead-producing states are Missouri, Idaho, Utah, and Colorado. In Missouri it is probable that the present rate of increase could be kept up for at least fifty years. The other states could keep up the present production for many years but could not greatly increase it without exhausting the supply.

As with most mineral resources in the United States, it is only the richest ores that are now drawn upon (except where lead is a by-product extracted with some other ore). If prices would advance, so as to make the low-grade ores profitable, the amount of our resources would be greatly increased.

There is little waste in the mining or smelting of lead ores, and the slag, the waste, is always ready to be used again. In the refining and concentrating of lead the loss often amounts to as much as fifteen per cent. or twenty per cent. The best way to prevent final loss is to store all refuse until such time as the reworking becomes profitable.

Improvement in methods has been great in the last fifteen years but more economical methods everywhere will be one of the necessities of the future. We can see that the lead resources of the United States are not large and that when our own supply is exhausted we can not turn to the rest of the world.

The waste in mining is not large, and most of it can not be avoided at present prices; so that for the conservation, which we see is so important, we must turn to the uses of lead. The most necessary of these is for lead pipes in plumbing. Another use is for war supplies, which not only makes heavy drains on our stores of coal and iron, but also on lead, which is much less plentiful.

One ton out of every three produced in the United States is used in the manufacture of white lead and consumed as paint. This, of course, is entirely lost, and it seems that some other material might be used, instead of so valuable a mineral, especially when the resource is not abundant. White lead is used more than any other substance for paint, although zinc white has come into considerable use in the last few years. No other nation uses lead paint to such an extent as does the United States, partly because no other nation could afford so general a use of such an expensive material, and partly because so many wooden buildings are erected. By using brick, stone, or cement, of which we have practically an unending supply, to take the place of wood, our store of which is rapidly disappearing, we could avoid much of the drain on our mineral resources which are used for paint.

As production and price advance a greater quant.i.ty of lead is remelted.

About 25,000 tons are returned to use each year.

ZINC

Zinc is a whitish metal. It is used in galvanizing iron to prevent its rusting. It is used also in the manufacture of white paint, which consumes about one ton out of every six tons mined. This, of course, is permanently lost, but the price and its value as a resource is much lower than lead. This takes more than half of the entire product. The remainder of the output is about equally divided between bra.s.s and sheet zinc. All these uses are extremely necessary and it is believed that the production of zinc will rapidly increase for many years.

The United States is the largest producer, Germany ranks second. Large amounts are mined in Australia, and very large deposits, entirely undeveloped, are said to exist in Africa. In 1880, the United States produced 23,000 tons of zinc; in 1907, 280,000 tons. This indicates the rapid rate at which we are increasing our use of zinc.

If the same rate should continue, in 1920 we should be using 475,000 tons, or almost a billion pounds, and if zinc oxide should take the place of white lead in painting to the extent that now seems probable, the quant.i.ty would be still further increased.

Missouri is by far the heaviest producer of zinc, having a little more than half of the output. New Jersey ranks next, then Colorado, Wisconsin and Kansas. Some of the other western states each produce small amounts.

Most of the pure zinc ore is mined at a depth of from one hundred and fifty to two hundred and fifty feet and occurs in sheets, but a large part of the ore is a by-product obtained from the reduction of other ores. In New Jersey the zinc alone is found in a single region, where it was estimated a few years ago that there were eight million tons, of which two and a half million tons have been mined since 1904. The zinc in Missouri, Wisconsin and Kansas is found alone or underlying lead deposits, while that of the western states is almost always found in limestone, and is mixed with silver, copper, lead, and, more rarely, gold. In these states there has been little attempt to discover zinc; in fact, ores containing zinc have been rather shunned because of the difficulty in extracting them.

It is thought that our resources of zinc, especially in the West, have just begun to be developed, and that the supply, even at the present rate of increase and at present prices, will last many years. However, with increasing use for the product, we can not be sure of supplies for more than a generation; and in view of the importance of zinc it becomes necessary to inquire into its wastes.

In no mineral is the waste more startling than in zinc. In Missouri it is necessary to leave supporting pillars as in coal mining. This can not be remedied, as the use of timbers is too expensive, but it causes a heavy loss. In the West, owing to the expensive treatment and shipment, much of the low-grade ore is left in the ground. In refining the loss is enormous, often as much as forty per cent. In order to produce zinc at a low cost there must be a heavy loss of metal. Better plants and equipment for refining, and the saving of all refuse for later use will be necessary if we are to conserve the zinc supply for future generations.

MISCELLANEOUS

The supplies of many of the materials used in buildings and bridges, such as stone, gravel, clay, cement and lime are so great that they appear inexhaustible, and need of care in their use is not so much to be considered as is their development to take the place of other resources.

In the past they have not been used freely because wooden buildings have been so much cheaper; but cement, concrete and brick are now manufactured much more cheaply, on account of improved methods, while the price of lumber has been increasing rapidly. Within the last ten years, the value of cement manufactures has increased nearly six times.

In 1900 we used seventy pounds of cement for each person; in 1907, two hundred and twenty-eight pounds. The value of brick and other products made from clay has doubled in the same period and is now $160,000,000, while the value of building-stone quarries is three times as great as it was ten years ago. There are many reasons why these materials should take the place of wood; as they are stronger, more durable, do not require paint, and are so much less liable to loss by fire.

The waste of minerals used in building is due to improper and reckless methods of taking them from the ground and preparing them for market and in careless methods in manufacturing.

Of such minerals as quartz, grindstone, millstone, emery stone, mineral paints, talc and salt, there seems to be enough to meet the needs of the future as well as the present. Such supplies as sulphur, asphalt, magnesia, borax, and asbestos, as well as coal and iron, are not very plentiful. If used carelessly, they will be exhausted in a few years; if wisely, they may be expected to last beyond the limits of the present century.

Our supplies of quicksilver, antimony, graphite, mica, tin, nickel, platinum, and many minerals less well known, as well as our petroleum, natural gas, copper, gold, silver, lead, zinc, and phosphate rock will be almost exhausted well within the present century unless large new deposits are discovered.

REFERENCES

Report of National Conservation Commission.

The Conservation of Mineral Resources. U. S. Government Reports.

Report of the U. S. Geological Survey.

Production of Gold in 1908. U. S. Government Reports.

Production of Silver in 1908.

Production of Lead in 1908.

Production of Zinc in 1908.

Production of Structural Materials.

About twenty pamphlets on other minerals.

CHAPTER IX

ANIMAL FOODS

GRAZING

Food is of two cla.s.ses: vegetable, which comes directly from the earth, and animal, which has fed on vegetable life. This is, of course, a more concentrated form of food, and much less of it is needed to sustain life.

For the plentiful supply of vegetable food we must depend upon the fertility of the soil, as we have seen. Our animal food can not be cla.s.sed among our natural resources, but as a product of them, and requires the same care and wise use.

In the early history of our country natural animal food was abundant.

Fishes swarmed in the sea, lakes, and streams. Wild turkeys and other game birds, deer, and bison formed a large part of the food of our forefathers. But these have been gradually disappearing. We have caught and destroyed so many fish that we have only a fraction of our former number. The game birds have disappeared either because they have been killed in great numbers or because their nesting-places have been destroyed. Of the big game nothing is now left except in a few remote regions, and it is growing less plentiful each year.

Although large quant.i.ties of fish and game are marketed every year at certain seasons, they form a small fraction of the animal food required in the country, and we must now depend for most of our animal food, not on that which was at first given us for a natural resource but on that raised by man.

The poultry--the chickens, ducks, geese and turkeys; the cattle, beef and dairy, the hogs and the sheep that are raised in such vast numbers have taken the place of wild game. The cultivated varieties have higher food value, and are far more satisfactory, since they are ready for use at any time.

The conservation of our animal food resources presents a different problem from any other. It is true that we have wasted and exhausted our natural food supplies, but we must remember that to a certain extent their preservation was neither possible nor desirable. They have been driven out by advancing civilization.

Wild birds and animals leave as the forests are cut out, destroying their natural homes. Many of them can not be kept in captivity, so this supply never could have been regulated. It was necessary to destroy some of them to insure man's safety, and others were needed for his use.

But we can take their places with other animals which are better fitted for our food, and it is the task of keeping up a sufficient supply of these on the most suitable land and under conditions that will yield the best results, that const.i.tutes the problem of the conservation of our animal food resources.

The raising of poultry and live stock on a large scale is a separate occupation, usually followed in a scientific manner and it is not of that industry that we need to speak, but rather of the benefit to every farmer and to the dwellers in small communities, of raising at least a part of the animal food used by the family.

Every farm has some bits of unoccupied land that can be fenced off for poultry. The gleanings from the fields will supply their food, and they will furnish meat and eggs for the family throughout the year, with enough left to sell to provide other comforts.

Live stock, cattle, sheep and hogs, as well as goats, horses and mules, are profitable to every farmer. Many farms have woodland; land that overflows at some seasons, and so is unfit for raising crops; or some rocky unproductive land where stock can be raised more profitably than anything else, and if every farmer would use all the land not suitable for farm crops for pasture land the problem of an abundant meat supply, of dairy products and of fertilizers to enrich the soil would be largely solved. Some farming experts advocate letting each field in turn be used for pasture every five years, because the stock raised on it is equal in value to any other farm crop, and because the rest and fertilization almost double the value of the succeeding year's crop.