1.48 Average amount of gravel washed per inch water, cubic yards, The following tabular statement shows the workings of a mine on four per cent. grades, high banks, and with great hydrostatic pressure. The advantages of heavy grades and pressure, over the minimum La Grange grades, are clearly shown by the quantity of material moved, and a comparison of the work and costs will be of interest to those engaged in hydraulic mining. (See Tables IX and X.) Table IX. No. 8 Claim, North Bloomfield Gravel Mining Company.† 180 ft. 1,858,000 $74,271.77 $53,088.83 4.80 19.1 4.0 .77 2.07 260 ft. 2,919,700 192,735.73 94,823.75 4.17 27.5 6.6 .74 2.45 * Material account excludes $8807.81 on hand. † For details see Reports of the North Bloomfield Gravel Mining Company for years 1874-6. : Less cost of melting and refining. Exclusive of costs of melting and refining. The question of the yield and costs of working hydraulic claims is one of great interest to the engineer. In estimating the production of gravel mines, the calculation of a given number of cents per cubic yard refers to the entire quantity of gravel moved or to be moved, since it is impracticable to wash out the gold-bearing strata without moving the entire superincumbent mass. The yield is, therefore, apportioned to the total quantity of ground washed. Having prospected a claim, and ascertained the approximate value of the gravel per cubic yard, grade and quantity of available water being known, its yield can be estimated for a reasonable period. In discussing the question of working unexplored localities, and even those already developed, it is to be observed that there are no known means which enable one to predetermine accurate economical results. Therefore, in estimating the yield of gravel properties, even under the best of circumstances, the most careful opinion drawn from immediate facts is, owing to the nature of deposits, necessarily qualified. THE STRENGTH OF WROUGHT IRON AS AFFECTED BY ITS COMPOSITION AND BY ITS REDUCTION IN ROLLING. BY A. L. HOLLEY, PH.B., M.I.C.E., NEW YORK CITY. (Read at the Philadelphia Meeting, February, 1878.) THIS paper is an abstract and a discussion of results obtained the United States Test Board in experiments upon 14 brands of wrought iron, most of which are well known and of high repute.* The iron was all intended for chain-cables; it was tested in the form of bars, usually of nine sizes, from 1 inch to 2 inches round, and also in the forms of single links and short chains. Not less than 2000 tensile tests were made, each showing elastic limit, elongation, and reduction of area. This work was done with conspicuous intelligence and fidelity, at the Washington Navy Yard, by Commander L. A. Beardslee. Some important practical results and principles which he has developed, and others which he has confirmed, will be referred to. The chemical part of this work consists of 42 complete analyses (including slag), by Mr. Blair, chemist to the Board. EFFECTS OF COMPOSITION ON STRENGTH. Variations in the physical qualities of iron may be due to different composition, or to different treatment in manufacture, or to both these complex causes. In order to determine the specific causes of variation, one class of altering conditions should be made to vary largely, while the other classes should be kept uniform. Then another class should be varied, and so on, until the value of each is ascertained. As all the irons under consideration were intended to have that purity and refinement which was deemed indispensable in chain-cables, their chemical analyses are perhaps more important in proving that physical variations result chiefly from treatment, than in pointing out the specific effects of certain ingredients. While the subject of treatment-especially the increase of strength by greater reduction in rolling-may be the more important one, it can be best appreciated after we have familiarized ourselves with the general chemical and physical characters of the irons. The typical facts are given in the following tables. * As the present object of the Board is not to compare the products of different makers, but to discover the physical effects of various composition and treatment, the irons are designated by letters rather than by their trade names. Table I. Analyses of Irons Used in Making Chain Cables. A 2.. 0.007 B1 7-16........ C 12.. D 1............. 0.178 0.139 0.021 0.031 0.172 0.068 0.078 1.210 0.047 0.037 0.028 0.570 0.045 0.097 0.012 0.023 0.026 0.020 0.071 0.016 0.023 0.029 0.038 0.018 0.031 0.026 0.546 J1 11-16........... 0.005 J 134.. 0.003 0.223 0.295 0.035 0.029 0.213 0.303 0.051 0.007 0.011 0.004 0.154 0.257 0.033 0.053 Trace. Trace. 0.013 1.724 0.005 0.161 0.156 0.062 0.018 0.048 0.016 0.049 0.540 0.006 0.134 0.143 0.071 0.021 0.046 0.013 0.037 0.354 Trace. 0.065 0.105 0.453 0.006 0.008 Trace. 0.011 0.326 Trace. 0.073 0.098 0.328 0.005 0.008 0.013 0.013 0.192 Trace. 0.067 0.098 0.512 0.029 0.010 0.010 0.016 0.308 0.212 0.014 0.006 0.010 0.013 0.452 0.248 0.016 0.008 0.008 0.018 0.103 0.229 0.019 0.007 0.015 0.018 0.175 0.042 0.040 0.006 0.026 0.026 0.248 0.174 0.026 Trace. 0.314 0.110 0.340 1.096 0.233 0.204 0.034 0.059 0.370 0.058 0.029 0.884 0.317 0.259 0.039 0.021 0.374 0.098 0.175 1.034 0.219 0.159 0.063 0.022 0.328 0.052 0.039 0.674 0.031 0.340 0.053 0.211 0.182 0.055 Trace. 0.005 0.078 0.073 0.042 0.005 0.046 0.034 0.037 0.974 0.057 0.848 Slag and oxide of iron. |