78 
Proceedings of the Royal Society of Edinburgh. [Sess. 
other respects the behaviour of the natural oxide was similar to that of the 
artificial material. Little or no effect was observed in these at temperatures 
below 275° C. Practically no magnetic effect was observed in a bar of 
Double 
Deflection . 
20 
mm 
Alcohol -Paste Bars of Ferric Oxide dried a<?d 
Constant Temperature ig Hydrogen. 
400 ®c . 
K X * X ft- 
275 *C 
■*— *300 "c. 
(K 
2S0 °C. 
•H 
2 
Seated cat 
2^ Pours 
hsematite ore which was heated in hydrogen at 275° for 3J hours ; whereas, 
at the same temperature, a notable amount appeared in the bars of ferric 
oxide, and in a much shorter time than the above interval. 
A great change of volume and of colour takes place at temperatures above 
500° C. in a bar of ferric oxide as the effect of heating in hydrogen, alcohol 
vapour, or air. The bars contracted in some cases to less than half their 
60 ' 
SO 
30 ' 
20 
10 
'z 
,^x>o \ 
200°, 250°, 275 °C. 
Haematite Bars heated at Coqstarit 
Temper hi ure it? H jdroyer? . 
I Hz 2 2 -, 3 
Constant High Te^pcrature in Hydrogen. 
4 Hours. 
initial volume, and hardened into compact, rigid bars. At the same time 
their dark red colour changed to a dark grey-black. 
Discussion of Results. 
The observed numbers, from which the curves have been drawn, are 
liable to be affected by certain causes, the chief of which are : (a) coil effect, 
( b ) shortening of the bar as a result of heating, and (c) errors of temperature 
measurement. 
(a) Coil Effect . — Errors of observation may arise through displacement 
of the magnetising or compensating coil during the course of a prolonged 
heating and after compensation has been effected. We have called the 
deflection thus introduced the coil effect. It makes its appearance on a 
very slight motion of either coil, since these coils have to be set as close to 
