.50

concrete practically waterproof is a long step toward a still wider use. The use of cement concrete on the farm seems to have almost unlimited possibilities. Mining work is requiring increased quantities of cement.

Dollars

3.00

2.75

2.50

2.25

2.00

1.75

1.50

1.25

1.00

.75

FIG. 8.-Range in average price per barrel of Portland cement, 1880-1913.

and concrete for surface structures, shaft linings, and roof supports, where it replaces wood. In the rapid development of concrete construction utility has naturally received greatest attention. The

artistic possibilities of concrete are now beginning to receive a fair share of attention.

Although Portland cement was invented early in the nineteenth century by Joseph Apsdin, of Leeds, England, the greatest development in methods of manufacture and quality of product has really taken place in the United States since 1890. To-day the superiority of practically all the American Portland cements is recognized throughout the world. In part this recognition is an outcome of the United States Government specifications that practically all cements must pass, as they are used on Government works.

One of the present needs of the cement industry is for a comprehensive survey of available supplies of sand and gravel for use with Portland cement for concrete construction-especially for concrete roads. These are materials the distribution of which counts for most in determining their economic value.

ASPHALT AND ALLIED BITUMENS.

The marketed production of natural asphaltic material in the United States in 1913 aggregated 93,000 short tons, valued at $751,000. In 1882 the entire output of asphaltic material in the United States came from a single locality in California and amounted to about 3,000 tons, valued at $10,500.

Imports of natural asphalt for consumption in the United States are at present almost wholly from Trinidad and Venezuela, the quantity brought in during the fiscal year ending June 30, 1914, aggregating 181,000 long tons, valued at $918,000.

Exports of asphalt (largely oil asphalt) from the United States in the same period amounted to 50,000 long tons, valued at $1,131,000, and in addition asphalt products manufactured in the United States, amounting in value to $362,000, were exported. Exports of crude asphalt were chiefly to Canada, Germany, West Indies, Great Britain, Argentina, and Brazil.

Oil asphalt is manufactured from petroleums produced in the Gulf coast fields and in California, as well as from petroleum of the same general type imported from Mexico. In 1913 some 437,000 short tons of oil asphalt, valued at $4,500,000, were manufactured in the United States from petroleum of domestic origin, and in addition some 114,000 tons, valued at $1,700,000, were manufactured from petroleum of Mexican origin. The utilization of the Mexican petroleum for this purpose is purely a matter of convenience in refining the petroleum, since ample supplies of suitable petroleum are available in the Gulf coast, Illinois, Wyoming, and California fields. Natural asphaltic rock occurs in the United States in western Kentucky, southern Oklahoma, western Texas, California, and Utah, and has recently been discovered in large quantities in the Philip

pine Islands. Solid bitumens occur in West Virginia and Oklahoma, but the most important deposits are in Utah and western Colorado.

Natural asphalt, as suitable for paving purposes as that from Trinidad and Venezuela, is not found in the United States; but by adding asphaltic residues from petroleum the natural hard asphalts and solid bitumens available in this country can be made into efficient substitutes, which guarantee the independence of the domestic paving industry should the foreign supply of asphalt be cut off.

Manjak is imported from Barbados for use in the varnish industry. No deposits of manjak of commercial importance are known in the United States, but efficient substitutes are available in the high grade gilsonite and elaterite deposits of Utah.

Ozokerite, a native paraffin wax that has been imported for many years from Galicia, occurs in Utah, but because of the cost of extracting the mineral and of transporting it to eastern markets the deposits have remained undeveloped. For all practical purposes paraffin wax prepared as a by-product of petroleum refining is an acceptable substitute for refined ozokerite.

ASBESTOS.

The United States is not a large producer of asbestos, but there are asbestos deposits in Georgia, Arizona, California, Virginia, and Vermont. The domestic production amounted to 7,600 tons in 1911, while the imports, largely from Canada, amounted to ten times this quantity. The Canadian asbestos mines at Thetford, Quebec, are the largest in the world, and the United States absorbs nearly three-fourths of their output. This country exports considerable quantities of articles manufactured from asbestos.

Asbestos is the most important fireproofing material known. Its fibrous structure adapts it to a wide range of applications from woven fabrics, such as theater curtains and articles of clothing, to various forms of asbestos board and paper, pipe covering, shingles, plaster, etc. For a few purposes asbestos finds a competitor in magnesite, which is also a refractory material, but for most of the purposes to which it is applied it is practically without a rival.

CHEMICAL MATERIALS.

PHOSPHATE ROCK.

Thirty-five years ago the production of phosphate rock in the United States was 211,000 long tons. During 1913, production amounted to 3,111,000 long tons and exports to 1,366,000 long tons, or nearly 44 per cent of the total production marketed. Thus it will be seen that in 34 years the production of phosphate rock in the

United States has increased nearly fifteenfold. The accompanying curve, fig. 9, shows graphically the marketed production and the exports of phosphate rock during the past 10 years.

FIG. 9.-Curve showing production and exportation of phosphate rock, 19041913. (Note that exports tend to diminish compared with production.)

As the figure shows, a very large part of the phosphate rock is shipped abroad, but the amount exported, compared with the total quantity marketed, shows a tendency to diminish. The quantity of phosphate rock or phosphate-bearing compounds imported into the United States for use as fertilizer is exceedingly small.

The known phosphate producing areas in the United States are as follows: (1) In middle Tennessee; (2) along the western side of the Florida peninsula, extending 25 miles inland; (3) on the South Carolina coast, chiefly near Charleston; (4) a large area in Utah, Idaho, Wyoming, and Montana. In addition, there are important deposits in the Blue Grass region of Kentucky, and less well-known areas in Arkansas and elsewhere. Thus it will be seen that the important phosphate-bearing areas are not confined to any one district of the country but are widely scattered and are available to all parts of the United States. Most of the rock exported has been produced in Florida and Tennessee.

Phosphate rock is used chiefly in the manufacture of fertilizers, especially the so-called complete fertilizers. For this reason it is a commodity of vital concern to the farming industry in the United States and hence to all the people. There are no substitutes for it. Consequently the quantity of phosphate rock available for future

8161°-INT 1915-VOL 1-13

generations and the efficient utilization of this supply are of paramount interest and importance.

Calculations of the probable future life of our phosphate reserves have been made, but these calculations are subject to change as new factors arise for consideration. Among the more important of the new factors, that will tend to prolong the life of the deposits, especially those in the East, is the extensive introduction of improved mining and milling methods, by which deposits that were thought to have been worked out and tailings dumps and waste ponds from old phosphate mills are being reworked, and lower-grade rock is being mined at a profit.

Through the introduction of such methods deposits in Tennessee will yield rock for many years to come and the experience gained in Tennessee will be applied in the practically virgin central Kentucky field.

Nearly all the "hard rock" mined in Florida is shipped abroad. The life of the hard-rock field has been estimated at 25 to 100 years, depending on the rate of production. Very few new deposits are now being discovered and many of the old ones are now worked out. In washing the phosphate rock there have been large losses. In time some of the refuse will be retreated and losses will be greatly reduced. The mining of pebble rock in Florida has grown rapidly and in 1913 the output exceeded 2,000,000 tons. The deposits of this rock are so large that their end is not in sight.

A recent estimate of the phosphate rock in the South Carolina field indicates the presence of 5,000,000 tons of 60 per cent rock in the ground which will become workable when improved machinery is devised. Other estimates have been larger. The output of South Carolina rock in the past two years has been slightly in excess of 100,000 tons, and at this rate the field may be expected to last at least 50 years.

The known extent of the western phosphate reserves has been greatly increased in the past few years through the work of the United States Geological Survey which has resulted in including more than 2,660,000 acres of land in the phosphate reserves of the United States. Most of this land is in Idaho and Wyoming; some in Montana and Utah, and some in Florida. The work of surveying the western phosphate lands is still going on. Clearly, however, the United States is independent of the rest of the world as regard phosphate rock, and can produce enough for its own needs for an unknown number of years to come.

Phosphate rock is relatively insoluble, and the phosphoric acid it contains is converted into the easily soluble form, and thereby made readily available as plant food by treating the rock with acid. A cheap powerful acid is needed, and thus it happens that an