ACTION OF HEAT ON MAGNECilYSTALS. 
173 
the higher temperature. The force returns perfectly upon the restoration of a lower 
temperature. There is no permanent disturbance of the specific magnetic capacity, 
nor anything like magnetic charge. The loss is not in arithmetical progression, but 
greater for an equal number of degrees at lower than at higher temperatures ; and 
is best represented by a regular curve as the mean line. The two chief series agree 
very well together, and the third series, at low temperatures, is in near accordance 
with either. The loss of power at low temperatures, as 0°, is for the same number of 
degrees of elevation, three times as much as it is for temperatures about 270 ° or 280°. 
3409. The return of this and other crystals to their first condition by return of 
temperature, combined with the observations made with iron, nickel, &c. (3424.), 
shows that the magnet, as a source of power, remained unchanged by the variation 
of temperature from 0° to 300° in the magnetic field. 
3410. This tourmaline crystal (33/7.) being hung between the poles of the great 
electro-magnet, was raised by a spirit-lamp to a full red heat, and then set well with 
its axis equatorially, though with diminished power ; so that high temperature does 
not take away its magnecrystallic character : on cooling it returned to its first higher 
condition. On a former occasion I found that a like, short, thick, black crystal lost 
part of its power by the heat of a spirit-lamp flame, but on cooling, the tourmaline 
became very magnetic, pointed axially, and was strongly attracted. The latter 
effects were traced to a portion of peroxide of iron on one part of the crystal, which 
had been reduced to protoxide or even lower, by the vapour and heat of the spirit- 
lamp: digestion in hydrochloric acid removed this iron and restored the crystal to 
its first condition. The fact shows, that a temperature which takes away the high 
paramagnetic condition of iron or its protoxide could not destroy the peculiar con- 
dition of tourmaline as a magnecrystal. 
3411. Carbonate of iron . — The crystal of this substance before described (3379.) 
was suspended in an oil bath, and carried through temperatures varying from 4° 
to 293°. Its upsetting angle was 96°. The results are in the diagram marked F. 
In another set of experiments, results were obtained about 0° and 60°, and are added, 
being marked G. The whole forms a very consistent series of observations, showing 
progressive loss of power with elevation of temperature, the diminution being much 
greater at low than at high degrees ; and, on the whole, very great for the range of 
temperature employed. The loss of power about 0° and 32°, is four times as much 
as it is at 280° for an equal number of degrees. The whole power at 300° is 135 ; 
at 0° it is nearly tripled, being 380. 
3412. When carbonate of iron crystallized, is heated, either in air or oil, up to or 
above a certain high temperature, it is almost sure to fly to pieces like a Rupert’s 
drop. By perseverance, and by selecting the larger fragments when the breaking-up 
took place in oil, I obtained three pieces, which could be raised by the flame of a 
spirit-lamp to a red heat. Below a very dull red heat these crystals were always 
magnecrystallic; more at lower temperatures and less at higher: — regaining power 
MDCCCLVI. 2 A 
