IMPORTS INTO THE UNITED STATES.

Imports of thorium nitrate are shown in Table 8 and of thorium oxide and other thorium salts in Table 9. In 1914, 99.5 per cent of the thorium nitrate was received from Germany, 0.3 per cent from England, and 0.2 per cent from Austria-Hungary. Of the thorium oxide, 54 per cent was received from England and 46 per cent from Germany. Import statistics for cerium nitrate are not shown separately, but in 1914, 2,124 pounds, valued at $1,522, were imported from Germany.

The export statistics for thorium nitrate are not shown in Commerce and Navigation of the United States, and data compiled by the Tariff Commission can not be published without revealing confidential information. It is worth noting, however, that the export trade did not begin until 1914, although in that year considerable quantities were exported. In the following years the exports continued to increase and very appreciably exceeded the imports.

Manufacturers of thorium nitrate are able to take advantage of the drawback provision of the tariff act by which a "drawback" or refund of duty (minus 1 per cent) is paid on imported monazite sand from which thorium nitrate is manufactured for export. Thus, in 1918, 89,835 pounds of thorium nitrate were manufactured for export from $44,338 worth of monazite sand, on which a drawback of $10,973.67 was paid.

TABLE 8.-Imports of thorium nitrate for consumption in the United States, 1909-1920.

TABLE 9.-Imports of thorium oxide and other thorium salts for consumption in the

Fiscal years.

United States, 1914-1919.

PRICES.

Market quotations for thorium nitrate are not reported in the scientific and trade journals, but the following table (adapted from Bureau of Mines Technical Paper No. 110) shows the fluctuations that have occurred in the price of thorium nitrate in Europe and the United States from 1894 to 1919.

The price January 1, 1920, was $3.75 per pound.

TABLE 10.-Estimated prices of thorium nitrate in Europe and the United States, 1894–

1919.1

The prices from 1914 to 1919 were furnished the Tariff Commission by Dr. Hugo Lieber, 23 East Twentysixth Street, New York City.

F. o. b. Hamburg, charges for container to be added.

Price to April, 1916, was $4.25; from May to October, $6.50; and from October to December, $7 per pound. Prices in Germany during 1919 are reported to have varied from 80 to 110 marks per kilogram.

TARIFF CONSIDERATIONS.

The manufacture of thorium nitrate in the United States became well established during the war and considerable quantities are now being exported to Europe. It is a question whether American manufacturers will be able to hold this export trade under normal conditions, but the home market will probably be well supplied by the domestic producers.

There is, however, the possibility that the European manufacturers of thorium nitrate will secure their raw material at a lower cost than the American manufacturers who are forced to pay an import duty of 25 per cent ad valorem. If, therefore, the former arrive at lower production costs, it is obvious that they will attempt to export to America, which has always been a profitable market for this product. Gas-mantle scrap, which is dutiable at 10 per cent ad valorem, is converted into thorium nitrate, and this is its only commercial use. The conversion is a very simple process in comparison with the complicated manufacture of thorium nitrate from monazite. Gas-mantle scrap is chiefly thorium oxide and logically invites the same tariff treatment.

INCANDESCENT GAS MANTLES.

The incandescent gas mantle has developed from the research of the Austrian chemist, Dr. Karl Auer von Welsbach. About 1880 he began his study of the rare earth elements and attempted to utilize the property of thorium oxide and other rare earths of emitting an intense white light when heated in a Bunsen flame. In 1884 he patented the use, as a lighting medium, of a fibrous network composed of the oxides of certain of the rare earth metals.

It was not until about 1893, however, that Welsbach discovered that the maximum luminosity was produced by a mantle composed of 98-99 per cent of thoria and 1-2 per cent of ceria. The commercial use of the incandescent gas mantle may be said to have begun with this discovery, and when a few years later the large deposits of the raw material, monazite, were found, the commercial success was assured. A rapid spread of lighting by incandescent gas burners followed, and the gas mantle has, in a way, saved the gaslighting industry from the extremely severe competition of the electric light. The incandescent gas mantle gives the cheapest illumination wherever natural or manufactured gas is available. About 1900 the inverted mantle was invented. This form throws the light downward instead of upward and avoids a shadow, so that it is an important advance in the industry.

The world's consumption of gas mantles according to Kithil's estimate in 1915 amounted to about 300,000,000 mantles each year. V. B. Lewis, an English authority, gives the following estimate of the prewar consumption (1912):

The war to some extent indirectly caused an increased use of gas mantles. The demand for toluol for the manufacture of the important explosive, T. N. T., was so great and the supplies so much below the estimated requirement, that every possible means of increasing the supply had to be exploited. Much toluol could be obtained by removing it from illuminating gas, and plants for its recovery from this source were installed in many large cities. These "stripping" plants, as they are called, seriously damage the lightgiving power of gas when used in open-flame burners, but do not materially decrease the value of the gas for use with incandescent gas mantles or for cooking or heating purposes. This recovery of toluol for military uses indirectly stimulated the demand for mantles.

METHOD OF MANUFACTURE.

The fabrics used in the manufacture of mantles are cotton, ramie, and artificial silk (collodion). Ramie fiber gives the best quality, but is more expensive than cotton fabric, and the greatest number of mantles in this country are probably made from cotton. It is said that in Europe before the war 90 per cent of the mantles were made from ramie. The use of artificial silk is a more recent practice and very satisfactory results are obtained. Its ash is claimed to have a greater elasticity and there is the additional advantage that it does not require washing before impregnation.

The fiber is woven into the form of a hose or tube, bleached in an acid or alkaline bath, and very thoroughly washed in distilled water in order to decrease the quantity of mineral matter and to remove grease and other foreign substances.

After drying in a current of hot air, the fabric is then treated with the "lighting fluid," which is a solution containing from 25 to 50 per cent of thorium and cerium nitrates in the proportion of about 99 parts of thorium nitrate to 1 part of cerium nitrate. Small quantities of beryllium nitrate and magnesium nitrate are also added to the fluid in order to strengthen the ash skeleton. The fabric is then cut into suitable lengths and one end closed and sewed with asbestos thread, which afterwards forms the support for the mantle.

The next step, which is known as the "fixing" process, consists in strengthening the parts of the mantle which are to be subjected to the greatest strain. This is accomplished by treating these portions with a thorium solution containing a considerable proportion of alumina and the alkaline earths. If desired, the mantle may then be branded with the manufacturer's trade-mark by the use of a mixture containing didymium nitrate, which is a by-product in the manufacture of cerium nitrate. After the fabric is dried and shaped it is "burned off" and the nitrates converted into the oxides by an intense flame. This operation requires considerable skill and 2 or 3 per cent of the total number of upright mantles are usually damaged in the process. In the case of the inverted mantle the loss may run as high as 10 to 20 per cent. This gives rise to the material known as gas-mantle scrap which is saved and returned to the thorium-nitrate manufacturer for the recovery of the thoria and ceria. Practically 90 per cent of the gas-mantle scrap is obtained in this way and the remainder consists of worn-out mantles collected from the gas companies and other large consumers. The mantles which are not damaged in the heating process and have passed inspection for size, shape, and material defects are dipped into a solution of collodion, in order to give them the necessary strength to withstand the shocks of shipping.

This description refers chiefly to the cotton or ramie mantles. The types used for lighting railway cars and all artificial silk mantles require different methods of manufacture, although the same general principles are involved.

The number of mantles manufactured from a pound of thorium nitrate varies with the shape, quality, and size of the product. Johnstone states that in English practice 500 to 600 of the best quality upright mantles of the "C" size are made from a kilo (225 to 275

mantles per pound), and 1,000 per kilo of the cheaper quality (450 per pound). In American practice the number of mantles per pound of thorium nitrate averages about 325.

INTERNATIONAL TRADE IN GAS MANTLES.

Following the invention of the gas mantle the German and Austrian industries grew extensively and for a time supplied the demands of Europe and America. In 1906 Germany exported gas mantles to the value of $2,240,000, but since that time there has been a considerable decrease in her exportations, for a number of factories have been erected in almost every country. The exports of gas mantles from Germany, 1911-1913, are shown in Table 11.

TABLE 11.-Exports of gas mantles from Germany, 1911-1913.1

Source: Vierteljahrshefte zur Statistik des deustschen Reichs (1914).

The Austrian industry even before the war was no longer an important factor in the export trade, as may be seen by Table 12, in which her imports and exports of gas mantles are compared. The imports, which came principally from Germany, considerably exceeded the exports.

TABLE 12.—Imports and exports of gas mantles for Austria-Hungary, 1909–1913.

Source: Statistik des Auswärtigen Handels des Oster. Hungar. Monachie (1913).

24,251

$44,572

220

7,716

14, 182

2,205

$365

3,647

661

6,173

1,093

11,346

221

365

38, 140

70,100

3,307

5,470