TABLE 27. Sil. Sul. Phos. Mang. C. C. G. C. T. C. Variation I ............ TO 028 029 J9 •34 .82 48 Variation 2 ................ 21 .015 .031 .23 •59 1.09 Those making* a study of the reasons for such differences in results as shown by Table 27, will find that it is due to the fact that chemists are unable to know positively the correctness of their results without checking them by some known standard. Almost every trade possesses some standard by which its artisans can tell wliether their labors have been productive of the perfection desired. The appearance of the finished casting* indicates to the furnaceman or founder the result obtained from his iron. A trial of a machine or an engine demonstrates to the machinist or engineer the perfection lie has attained, but the completion of an analysis by a chemist presents no tangible evidence of the accuracy of his results. The only way a chemist can know the correctness of his results, or give others any assurance that his work is correct, is by having them checked by others, or by analyzing standardized drillings that have been determined by competent chemists to find whether results agree. The latter method of checking is similar to the use of standard weights to test the accuracy of scales. No laboratory is complete without its standardized drillings, any more than would be a furnace or foundry without standard weights for occasional testing of scales. This necessity has led many chemists heretofore to make their own standards. An observing person having- the opportunity to visit chemical labor- most close grained iron giving a slightly softer casting than the open iron, after the principles presented in Chapter 47, pages 337 to 339. However, there is no reason why any one should make it a point to insist on accepting only open or close grained iron in connection with exacting any certain specified analyses from blast furnaces, as the slight difference possible in the most radical cases of open and close grained iron can be regulated by a slight variation in silicon when making a mixture, and which anyone can easily do, if they so desire, "