25-i Magnetic At fraction of Oxides of Iron. 



any magnetic cfi'ect. The mixture was then put into AM* 

 bacco-pipc, and placed in the clear red heat of a common 

 fire : as soon as the pipe had acquired a red heat, it was 

 taken out. The mixture was put on a glazed tile to cool^ 

 and proved highly magnetic. 



I rubbed a portion of the original oxide in a glass mortar 

 with a variety of substances, as sulphur, charcoal, caitiphor, 

 Klher, alcohol, &c., and found that no effect was produced 

 •wuhout the assistance of heat. The heat of boiling water, 

 moreover, was not sufficient 3 bul bv the heat of melting 

 lend I procured magnetism. Small quantities of any in- 

 •flanmiablc matter in a red heat have an evident effect oa 

 the oxide. Hydrogen, aided by a red heat, renders the 

 oxide magnetic. Alcohol has the same effect. But if the 

 alcohol be diluted with water, though it may flame in the 

 iire, it will be incftectual, as it is driven 03" before the oxide 

 tjeco'mes sufficicnllv heated to receive its action. 



Such combustible substances as do not very readily part 

 with their carbonic element,, require rather longer conti- 

 nuance of heat than others ; for example, charcoal and cin- 

 ders, well burnt, must be longer in the fire to have their 

 full cfi'ect on the oxide, than dry wood, coal, or sulphur. \ 



But such substances as may be sublimed with facility, 

 will gradually quit the oxide, by a contmued application 

 fven of a low heat, leaving it nnmagnetic, as at first. 



How very small a portion of inflammable matter is re- 

 quisite to render a considerable quantity of oxide magnetic 

 is evident, since one grain of camphor dissolved in an ade- 

 quate portion of alcohol, and mixed with a hundred grains 

 of the oxide in a glass mortar, will, by a red heat, lender 

 all the particles of the oxide magnetic. 



As oxides of iron, therefore, are rendered magnetic by 

 Iieat, when mixed with inflammable matter, it may be un- 

 derstood why Prassian blue, su'phurets, and ores of iron 

 containing inflammable matter, become magnetic by the 

 agency of fire ; while at the same time it is observable that 

 these same ores revert to their nnmagnetic state, when the 

 heat has been continued sufiicientlv long to drive oiF the 

 whole of the inflammable matter : thus we find among the 

 cinders of a common fire calcined sulphurets of iron, di- 

 stinguishable by their red colour, unuKignctic when all the 

 sulphur is sublniied. 



My intention in this communication is to prove generally 

 that n)ere oxides of iron are not magnetic; that any inflam- 

 mable substances mixed with them do not render them . 

 magnetic until they are by heat chemically combined vvitk 



the 



