───────────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬───── Cubic │ │ │ │ │ │ │ │ │ │ centimeters│ 0.0.│ 0.1.│ 0.2.│ 0.3.│ 0.4.│ 0.5.│ 0.6.│ 0.7.│ 0.8.│ 0.9. of soap │ │ │ │ │ │ │ │ │ │ solution. │ │ │ │ │ │ │ │ │ │ ───────────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼───── 0.0│ │ │ │ │ │ │ │ 0.0│ 1.6│ 3.2 1.0│ 4.8│ 6.3│ 7.9│ 9.5│ 11.1│ 12.7│ 14.3│ 15.6│ 16.9│ 18.2 2.0│ 19.5│ 20.8│ 22.1│ 23.4│ 24.7│ 26.0│ 27.3│ 28.6│ 29.9│ 31.2 │ │ │ │ │ │ │ │ │ │ 3.0│ 32.5│ 33.8│ 35.1│ 36.4│ 37.7│ 38.0│ 40.3│ 41.6│ 42.9│ 44.3 4.0│ 45.7│ 47.1│ 48.6│ 50.0│ 51.4│ 52.9│ 54.3│ 55.7│ 57.1│ 58.6 5.0│ 60.0│ 61.4│ 62.9│ 64.3│ 65.7│ 67.1│ 68.6│ 70.0│ 71.4│ 72.9 │ │ │ │ │ │ │ │ │ │ 6.0│ 74.3│ 75.7│ 77.1│ 78.6│ 80.0│ 81.4│ 82.9│ 84.3│ 85.7│ 87.1 7.0│ 88.6│ 90.0│ 91.4│ 92.9│ 94.3│ 95.7│ 97.1│ 98.6│100.0│101.5 ───────────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴───── This table does not provide for the use of so large volume of soap solution for a single determination as former ones because the end-point becomes somewhat obscured in the presence of magnesium if more than 7 cc. is used. _Second method of standardization._—Dilute 100 cc. of the stock soap solution to 1 liter with 70 per cent alcohol. This dilute solution should be of such strength that approximately 6.4 cc. of it will give a permanent lather when 20 cc. of standard calcium chloride solution diluted to 50 cc. with distilled water is titrated with it. Determine the amount of soap solution required to give a permanent lather with 50 cc. of distilled water and with 5, 10, 15, and 20 cc. of standard calcium chloride solution diluted to 50 cc. with distilled water. Finally plot on cross-section paper a curve showing the relation of various quantities of soap solution to corresponding quantities of standard calcium carbonate solution and therefore to parts per million of hardness. _Procedure._—Measure 50 cc. of the water into a 250 cc. bottle and add to it soap solution in small quantities in precisely the same manner as described under the standardization of the soap solution. From the number of cubic centimeters of soap solution used obtain from Table 6 or from the plotted curve the total hardness of the water in parts per million of calcium carbonate.