142 
Manganese-bismuthide*) (MnBi). The rotation, which was negative at 
both ends of the spectrum (Fig 3), reached a positive maximum at 
530 uu. Points of inversion were found at 468 ug and 617 ue. 
Although the mirror was not very bright I was yet able to measure 
the rotation fairly accurately in spite of its small amount. 
TA Boe 
ef (2) Mn Bi (saturated) HILPERT 
N 1 (4) | £ (mm) | (min.) dà 
| 
25 | 435 | DD | — 1,65' | 013° = Ti 
25 | 450 | PEF |. Soe -| 0,076 78s 
so. |-.456 at S046) Doe 220. 
25 | 483 | + 48 | +072 | 005 —65 » 
aje 508 BA de 16 1,03, 2 Ms 
21 530 | + 90 | +148 | 003 =2 » 
21 | 567 | +63 | 4094 | 0,03 =28 » 
70 | 615 | + 03 | +0,045 |_ 0,015 =333 » 
Bp ATL A oe ee oes 
IRON COMPOUNDS. 
Iron carbide (Fe,C, Cementite). As the material contained for the 
most part cementite in needle-like crystalline layers mixed with other 
substances, the mirror was treated with sulphurous acid so that the 
cementite surfaces did not change their reflecting power while the 
other constituents were strongly darkened. Measurements carried out 
on six different parts of the surface yielded somewhat different 
results. Ail the curves however show a certain similarity viz. a very 
1) S. Huperr and Tu. Dieckmann, Chem. Ber. 44 p. 2831, 1911. E. Wepexinp 
and A. Verr, Chem. Ber. 44 p. 2665, 1911. 
