6	TESTS OF METALS AND OTHER MATERIALS, 1900.
The most interesting results pertained to the subsequent testing of the material which was exposed to zero temperature. Specimens which remained in storage one week, one month, or three months, followed by one or more days in the open air at 70° F., were low in strength in each group. The short initial period of setting between the time of guaging and when the material reached a frozen state and the final period of thawing, necessarily afforded an opportunity for the cement to acquire a certain degree of strength. The period of 0° F. was one of partial or perhaps nearly complete suspension of chemical action, as evinced by the strength displayed when finally tested. After thawing, the material rapidly gained in strength, but the evidence of the tests leads to the deduction that the interval of exposure to low temperature was detrimental in the subsequent attainment of strength when brought under ordinary atmospheric temperatures for the period of time covered by these experiments.
On ■the other hand, while the material which set at 39° F. did not equal the strength of that exposed to 70° F. for a corresponding period of time, yet the subsequent gain in strength after having been brought to 70° F. eventually placed it in a state of equality with the material set at the latter temperature only, and with instances in which there was a superiority in strength.
There were specimens subjected to higher temperatures, and the strength determined after they had cooled to the temperature of the open air.
The strength of glass, rough, ribbed, polished plate and wired, was determined in the condition of lights set in frames and under ordinary transverse loads. The limited available information on the strength of ׳ this material enhances the interest which attaches to these experiments.
Chemical analyses were made on the different classes of material, the results of which accompany the mechanical tests to which they refer, or are presented separately in tabular form.
A list of the private parties who have availed themselves of the facilities of the testing department during the fiscal year, under provision of the law, is appended.
The testing department building has been enlarged by the addition of a wing, providing rooms in which are located the engine and accumulator pump, the machine tools for the preparation of test pieces and the fabrication of special fixtures and supplementary parts of the testing machines, and a tank and furnace room, which is also used in the preparation of cement and concrete specimens.
This modified arrangement of the accessory apparatus of the testing department has enabled separate rooms in the main building to be set apart and used for metrology, photo-micrography, and pyrometry.
Very respectfully, your obedient servant,
John G. Butler,
Lieutenant- Colonel, Ordnance Department,
TJ. S. A., Commanding.
The Chief of Ordnance, U. S. A.,
Washington, D. C.