CHEMICAL AND PHYSICAL PROPERTIES, ETC. 207
Total carbon is that composing the combined and graphitic carbon united. Where the total is known and only the combined is stated, the balance necessary to make the total would be the graphite, and the reverse where the graphite is only known.*
Woolwich's experiments have proved that variations in the percentage of combined carbon are more effective in changing the grade of an iron than equal variations in graphite carbon. A slight increase in graphite, with the combined carbon remaining constant, creates very little effect in changing the grade to make a softer iron, but if a like change should be made in the combined carbon, having the graphite remain constant, the ratio would be greatly changed or the '' grade '' of the iron would be very much altered.
Silicon's chief office is to soften iron and aid the founder to regulate or cheapen his mixture. This was first suggested by Dr. Percy in the year 1850, but it awaited experiments in 1885 by Mr. Charles Wood, a founder of Middlesbrough, assisted by Mr. John C. Stead, the expert chemist, both of England, to first practically demonstrate the value and utility of silicon as a softener and its application to founding, a work which, it should be said, had its foundation laid in experiments conducted by Prof. Thomas Turner, at Mason College, Birmingham, Eng., the same being presented a few months later at the Glasgow meeting of the Iron and Steel Institute. The extensive publication of this paper is really responsible for the universal adoption of silicon as a softener in making mixtures of iron. The next to take up
*For further information regarding the "total carbon," see Chapter XXXIII, iron, and the larger the grain. For characteristic determinations of combined carbon in a fluid state, see Chapter LX, and the carbons, etc., in iron, as