one-sixth of the total carbon is left undissolved in the case of the
hardened disk. The authors then give a _resume_ of previous work on the
subject. In the second part they have investigated the action of
bichromate solutions of various strengths on thin sheet-steel, about
0.098 inch thick, which was cold-rolled and contained: Carbon, 1.144 per
cent.; silica, 0.166 per cent.; manganese, 0.104 per cent. Four
solutions were used. The first contained about 10 per cent. of
bichromate and 9 per cent. of H_{2}SO_{4} by weight; the second was
eight-tenths as strong, the third about half as strong, the fourth about
one and a half times as strong. In all cases the amount of solution
employed was considerably in excess of the amount required to dissolve
the steel used. A residue was obtained as before. With solution 1, the
residue contained, C, 1.021; sol. 2, C, 0.969; sol. 3, C 1.049 the
atomic ratio of iron to carbon was Fe 2.694: C, 1; Fe, 2.65: C, 1; Fe),
2.867 C, 1): sol. 4. C, 0.266 per 100 of steel. The authors conclude
that the carbon in cold rolled steel exists not simply diffused
mechanically through the mass of steel but in the form of an iron
carbide, Fe_{3}C, a definite product, capable of resisting the action of
an oxidizing solution (if the latter is not too strong), which exerts a
rapid solvent action upon the iron through which the carbide is
distributed.

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APPARATUS FOR EXTRACTING STARCH FROM POTATOES.