143 
strong negative rotation having a numerical maximum in the violet 
and indicating a decrease towards the ultra-violet. It falls steeply in 
the blue region until the green or yellow-green is reached and then 
increases again towards the red. The carbon atom of the carbide 
accordingly produces a considerable change in the dispersion curve, 
compared with that of pure iron (table 12). Four of the curves are 
represented in fig. 4 and tab. 6 to 9. The two other places gave a 
smaller rotation. A consideration of the etched figures on the surface 
show that a better agreement for such a complicated structure can 
hardly be expected. On this account the investigation of alloys appears 
altogether more difficult than in the case of well defined compounds. 
550 
Fig. 4. 
TABLE 6 
e=f(*) Iron carbide (saturated) HILPERT 
N | 2m) 4 (mm) ¢(min.) =e ae 
30 435 | —201,9 | —30,28’ | 0,05'=0,17/, 
25 450 | —200,0 | —30,00 0,03 = 0,10., 
20 466 |4—4 196.3. |= 20.42 | 0,02 = O0, 
20 dese 180.8.) = 28,48 | 2602-10075, 
20 BUB es fee |: — 27,13 0,02 = 0,07,, 
20 | 530 | —176,3 | — 26,45 0,01 =004,, 
20 567 | —176,0 | —26,40 | 0,02=0,08,, 
20 615 | —177,7 |. —26,66 | 0,01=—0,04,, 
20 675 | —180,1 | — 27,01 0,03 = 0,11 ,, 
