INVESTIGATIONS OF THE BUREAU OF STANDARDS
The January Technical News Bulletin issued by the Bureau of Standards, Department of Commerce, contains a number of interesting items on recent investigations by that bureau, among which are the following:
Accuracy of Electrical Measuring Instruments.
An exhaustive paper on “The Accuracy of Commercial Electrical Measurements,” requested by the Instruments Measurements Committee of the American Institute of Electrical Engineers has been finished and submitted to the chairman of the committee. This paper is scheduled to be given at the convention in February, in the hope of arousing interest in the further standardization of electrical instruments.
The paper discusses the accuracy required in commerical electrical measurements and the means of obtaining it, namely, proper choice, installation, use, and maintenance of instruments. Conditions of use, external disturbing influence, and features of design and construction affecting the accuracy for measuring voltage and current are mentioned. The sources of error in electrodynamic wattmeters are discussed, including the effect of instrument transformer errors. The principal factors affecting the accuracy of watt-hour meters are given. In conclusion, some improvements which should be soon forthcoming are mentioned.
Service Tests of Concrete-Floor Treatments.
A number of surface treatments for concrete floors have now been under test for 18 months. Some of the surface coating materials which appeared to be in good condition at the end of one year of service are now wearing away in places where they have been subjected to the greatest use. The panels which were treated with the chemical hardeners, such as magnesium fluosilicate, sodium silicate, and zinc sulphate solutions still appear to be in very good condition. The panels treated with a solution of aluminum sulphate have now been in use for about nine months and so far the results are very satisfactory.
A Substitute for Jute Burlap for Sand Bags Used in Military Work.
Preliminary laboratory tests have been completed in the investigation of substitutes for the jute burlap ordinarily used for sand bags by the Army. It has been shown that while paper does not equal burlap in tensile or bursting strength, it may, nevertheless, be made up into bags which will be of value for this purpose. Further tests are to be made on four types of paper, as well as on burlap and cotton fabrics, and all these materials will be subjected to weathering tests to determine their deterioration under service conditions.
Deterioration in the Strength of Paper After Storage.
As a result of tests upon approximately 150 samples of paper, stored since March, 1909, it is noticed that bonds and ledgers containing 100 per cent, rag did not deteriorate in bursting strength as much as printing, writing, and similar paper containing wood pulp. The loss in bursting strength for the first class of papers tested was about 11.9 per cent., while the bursting strength for the second class of papers tested was 20.4 per cent, less than when tested 10 years ago. While these conclusions have been derived from tests on about 150 samples, as noted above, a large number of additional samples will be tested soon, and the results studied to determine, if possible, the cause and amount of the deterioration of paper in storage.
Investigation of Chilled-Iron Car Wheels.
For over half a century the majority of the freight cars in use in the United States have been carried by chilled cast-iron wheels. These wheels have given general satisfaction even under the greatly increased stresses due to the heavy rolling stock now in use. It has been noted for several years, however, that failures of freight-car wheels occur quite frequently at the foot of long and steep grades. The cause of such failure appears to be the heating of the wheel produced by the prolonged application of the brakeshoes, this rise in temperature causing complicated stresses in the structure of the wheel. The stresses thus produced may be sufficient to cause cracking and failure and in all probability a derailment of the car under which the wheel is placed. In order to determine the exact temperatures in different portions of the wheel, after prologed heating of the rim, the Bureau has instituted a complete investigation of this subject. It is obvious that temperature measurements can not readily be made upon a wheel in service, and considerable ingenuity has been shown in perfecting a laboratory apparatus capable of producing conditions analogous to those met with on the road.