Possible Error Due to Density of Solution.-A source of error that may in certain circumstances assume more than negligible proportions lies in the fact that, in most of the calculations of slime density, the specific gravity of the solution is taken to be 1, as it would be if it were pure water, but it is obvious that the various substances in solution, such as lime, cyanide, zinc, and soluble constituents derived from the ore, will raise the specific gravity above that of water. In the case of simple clean ores, which require only weak solutions of cyanide and lime, the error due to this cause may be neglected but when dealing with more complex ores and more concentrated solutions it may materially modify the monthly ore tonnage as determined by this method. An article by G. H. Clevenger, H. W. Young, and T. N. Turner, in the Engineering and Mining Journal of December 19, 1914, deals with this subject in considerable detail. A list is there given of the specific gravities of the solution from a number of mills, showing a variation between 1.002 and 1.01, and two instances are cited to show the difference due to this cause. "Taking the specific gravity of the dry slime as 2.66 and the weight of a litre of the wet pulp as 1260 grams (sp. gr. 1.26). (a) If sp. gr. of solution 1.008, then the percentage of dry slime Showing a percentage of difference of 2.63. = = Again, taking sp. gr. of dry slime as 2.66 and the weight of one litre of the wet pulp as 1100 grams (sp. gr. 1.1). (a) Taking the sp. gr. of the solution as 1, the percentage of dry slime= 14.56%. (b) Taking the sp. gr. of the solution as 1.008, the percentage of dry slime = 13.47%. The percentage of difference in this case would be 7.49." So, when the stock solution contains an unusually large quantity of soluble salts, thus raising its specific gravity considerably above that of water, the error due to this cause should not be over looked. The above-named article gives the following table for ascertaining the correction to be made in each determination on account of the specific gravity of the solution in the pulp. The authors thus describe its use: = = "Let the specific gravity of the dry slime 2.66; the weight of one litre of pulp 1150 grams; the specific gravity of solution = 1.005. Required: The number of cubic feet of pulp to 1 ton of dry slime in the charge. In Table 9, at the intersection of the vertical column headed 2.66 and the horizontal column headed 1150, is found 133.3, the number of cubic feet of pulp to make one ton of dry slime when the specific gravity of the solution is 1. In the adjoining column opposite 133.3 is found 0.87, the number of cubic feet to be added to 133.3 for each increase of 0.001 in the specific gravity of the solution: 0.87 × 5 = 4.35 (total correction): 133.3 + 4.35 137.65 cu. ft. of the pulp specified necessary to make one ton of dry slime." = Moisture Determination Preferred in Certain Cases.—When a thick pulp is aerated by compressed air it often happens that the amount of air entrapped in the form of minute bubbles renders the Specific Gravity determination quite unreliable. By allowing the flask of pulp to stand for a few hours the level may fall from 1 to 2 inches, due to the escaping air, but a large proportion of the entrapped air will be held permanently thus increasing the volume to that extent. In such cases the only remedy seems to be to make a moisture determination by evaporation. It is not enough, however, to determine the relative weight of ore and moisture in a sample of given weight, because the contents of the tank are to be estimated by volume and that volume is occupied by a mixture of ore, moisture, and air, so the weight of pulp taken for the moisture sample should have its volume also determined in terms of cu. ft. in order that the weight of ore in a cubic foot may be accurately determined. For instance: 1 Litre = 61.031 cu. inches or 0.03531 cu. ft. 1 Cu. ft. 28.3174 litres So if 1 litre of pulp be weighed and dried the weight of ore and water in a cu. ft. of capacity can be found. Weight in Grams of One Litre of Wet Pulp 1.12 148.7 9.35 388.5 .96 138.8 9.50 394.3 9.55 1020 961.4 94.9 966.3 95.4 971.4 95.9 976.4 96.4 981.2 96.9 985.8 97.3 3.35 9.40 390.5 2.54 217.0 9.45 392.4 2.58 2.02 195.3 2.03 196.2 2.06 1.64 177.5 1.65 178.4 1.66 179.2 1.67 1.36 162.7 1.14 150.2 .57 396.2 330.1 283.0 9.60 398.0 9.65 399.9 6.43 334.7 4.56 286.9 1981 990.6 1017 100.5 97.8 995.2 98.3 999.8 98.8 1004 99.3 1009 99.7 1013 100.1 660.3 32.42 663.4 32.58 666.5 32.73 669.5 32.89 672.4 33.10 675.3 33.2 678.2 33.30 495.2 16.11 497.5 16. 19 499.8 16.27 502.116.35 504.3 16.43 506.4 16.50 508.5 16.58 9.69 401.7 9.74 403.4 9.79 405.1 9.84 406.8 9.88 6.46 336.1 2.11 201.7 141.5 1.00 142.2 1.00 142.8 1.01 143.5 1.71 183.4 6.49 337.6 1.73 1.43 1.20 1.03 145.3 1.03 4.66 293.1 4.68 294.3 4.70 295.5 3.48 256.4 3.50 257.5 3.51 258.5 1022 100.9 1026 101.4 1030 101.8 1034 102.3 1038 102.7 1042 103.1 1046 103.5 681.1 33.5 683.9 33.6 686.7 33.7 689.4 33.9 692.0 34.1694.6 34.2 697.2 34.3 510.7 16.65 512.8 16.72 514.9 16.79 516.9 16.87 518.9 16.94 520.9 17.00 522.9 17.07 408.6 9.92 410.3 9.97 411.9 10.02 413.5 10.07 415.1 10.11 416.7 10.14 418.3 10.18 340.5 6.58 341.9 6.61 343.2 6.64 344.6 6.67 345.9 6.70 347.2 6.73 348.6 6.75 291.9 255.4 4.77 298.8 4.79 3.56 261.5 3.58 2.76 232.4 2.77 2.19 209.22.20 1.79 190.2 1.79 1.48 174.3 1.48 1.24 160.9 1.24 4.72 296.6 4.75 297.7 1.06 149.4 1.06 |