74 
Proceedings of the Royal Society of Edinburgh. [Sess. 
The magnetic property acquired by heating in air persists when the bar 
is cooled, and under further heat testing the bar gives a heating curve which 
resembles that for natural magnetite. 
The set of Curves 3 is for three bars of Lucinena ore which had been 
previously heated for various periods in the gas furnace in air, and were 
then passed through heat cycles in the electric furnace. 
Lucinena No. 1 was heated for 100 minutes at 850° in the gas furnace, 
Lucinena No. 2 for 30 minutes at 600° (with little effect) and then an 
additional 10 minutes at 850°, and Lucinena No. 4 for 10 minutes at 850°, 
- Heat Cycles in Air. - 
the heat cycle being made thirteen days after the heating in the gas 
furnace. The slight maximum in Luc. 2 at 230° is no doubt of the same 
nature as that in Curve 2, R.S. 1, at 630°, and that referred to later on in 
other curves. It appears to be characteristic of the magnetic change in 
ferric oxide. 
The curves coincide to a remarkable extent ; they follow the heating 
curve of natural magnetite * up to 600°. It may therefore be concluded 
that haematite ore, even when containing a considerable amount of impurity 
(pure haematite contains 70 per cent, of iron), exhibits, after being heated 
to a high temperature in air, the magnetic characteristics of magnetite. 
2. Constant High Temperature. (See Curve 4.) 
The full line in the curve begins when the bar had reached a tempera- 
ture of 500°. 
When heated in air at 500° C., the ferric oxide, in the form of powder 
held in a copper tube, did not exhibit uniform behaviour ; but in each of 
the three specimens tested there was considerable gain in magnetic quality 
with time. In one case the deflection dropped to zero after about 2J hours’ 
heating. The average curve given for the three specimens is similar in 
* See Phil. Mag., Jan. 1904, curve 15. 
