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These test briquettes are inserted between the grips of the testing machine, shown in Cuts Nos. 8 and 9, and by the application of strain at the rate of 400 pounds per minute, give the results within the limits above mentioned.

For the tests for constancy of volume, small pats are made of the neat cement. One pat is kept in water and the other is kept in air and at the end of 28 days they are to show no disintegration, checking or cracking.

The range of specifications in this country is very broad, and no general system has been adopted, such as has been in Germany, and the variations between the requirements of specification causes no little trouble to the manufacturer. Generally speaking, however, American Portland cements, as contrasted with those made abroad, are showing not only as good but better results, and in this country, as well as in the export trade, are meeting the most exacting of requirements.

Growth of the Industry.-In view of the fact that Portland cement has been for the past thirty (30) years the main binding ingredient of the heaviest masonry in the largest pieces of construction in the world, it can readily be understood the difficulties that were met with in the introduction of American Portland cement.

In the early days of the industry, where the change from the well-known brands of foreign Portland cements to the American product meant but the saving of $2,000 or $3,000 in a building involving the cost of $1,000,000 or more, it was difficult for the American cement, which was at that time considered a doubtful experiment, to obtain a foothold. The prejudice was hard to overcome, but owing to the quality of the American product and the perseverance of the American manufacturer, American Portland cement was gradually forced into the market and by degrees won the laurels which it now wears.

Twenty years ago, the production of American Portland cement. amounted to 85,000 barrels per annum. The United States Geological Survey figures for the year 1901, show a production of over 12,700,000 barrels, and this enormous increase in the output of Port

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land cement has been made without diminishing the 8,000,000 or 9,000,000 barrels of natural cement which are still being produced. Practically the same amount of the latter grade of cement has been produced for the last five years.

Without going into the statistics of the production of natural cement at this time, the figures of the U. S. Geological Survey on the production of Portland cement in the United States for the last twenty years are as follows:

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It will be noted by the above table that up to the year 1889 that estimates of production merely were given by the U. S. Geological Survey, but since that period, the number of works has been included together with the actual figures covered by the report of the survey. The following diagram shows the domestic production, importation and total consumption of Portland cement in the United States in the last twelve years:

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GRAPHIC REPRESENTATION OF THE PRODUCTION, IMPORTATION AND TOTAL CONSUMPTION OF PORTLAND CEMENT IN THE UNITED STATES

FROM 1890 To 1901.

These figures show that the imports of cement, with some small variations, have remained constant since 1890, but the production of American Portland cement, which in that year amounted to only 335,500 barrels, or 15 per cent of the total amount consumed, has increased in eleven years thirty-five times and now supplies about 95 per cent of the demand.

The production and annual increase of the production for the past. twelve years is as follows:

The following table shows the products, imports, exports and consumption of all grades of cement, natural and Portland, for the past five years for "Mineral Industry of the United States." The figures vary from those of the United States Geological Survey, as all

1896

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