CALCULATING ANALYSES OF MIXTURES. 257
The total of i.oo parts giving* us 200.95 of silicon, one part will equal about 2.00 per cent, of silicon, the same as obtained by the methods shown in Table 39, and shows one method to be an excellent check for the other. It is true Table 39 only deals with the silicon, but it can be seen by Table 41 that its principles will .also hold good for figuring the percentages of any of the metalloids. It will be noticed that in obtaining the average percentages of the silicon, manganese, and carbon they are figured to the second decimal, and the sulphur and phosphorus to the third.
The grade of scrap iron used is judged by the appearance of its fracture after the plan described in Chapter XLIL, and the change which takes place in remelting the iron to reduce the silicon and manganese and increase the sulphur and phosphorus of the mixture charged is described in Chapter XLIV. This change is such that, with a mixture as per Table 41 and charged into a cupola, the resulting castings would contain about 1.70 to i.So silicon, .05 to .06 sulphur, .45 to .55 manganese, .48 to .55 phosphorus, and 3.75 to 3.90 total carbon.
While for definite calculations Tables 39 to 42 are presented, there are cases where one may utilize different percentages of silicon, sulphur, etc., by mere mental calculation, after the ideas seen on page 141, that may answer all practical purposes. While the rules of Tables 39 to 42 may appear, at first, complicated, to those unaccustomed to such computations, they would, with a little practice, soon find the methods very simple.ABLE 39.