320 PROCEEDINGS OF SECTION B. 



note upon the preceding paper, " Occurrence of Magnetite 

 in certain Minerals and Rocks," it appears — 



1. That native sesquioxide of iron and its hydrates, such 

 as haematite, goethite, hmonite, &:c. are themselves non- 

 magnetic, i.e. to an ordinary bar magnet, but' may contain 

 some magnetite. 



2. That sesquioxide of iron obtained by precipitation from 

 the acid carbonate of iron and probably from other salts of 

 iron is magnetic, or may be rendered magnetic by long 

 boiling or by heating at various temperatures up to redness, 

 and that such magnetic sesquioxide is free from any 

 monoxide. 



3. That magnetic sesquioxide of iron free from monoxide 

 can be obtained by heating the magnetic oxide, as first shown 

 by Robbins. 



4. That ordinary rust produced by the oxidation of metallic 

 iron is usually magnetic, and often polar. Magnetic rust 

 usually contains more or less ferrous oxide, and may accord- 

 ingly be regarded as x FeO, y Fe^Og, i.e., varying mixtures 

 of FeO and Fe.^Og, and of their hydrates, being well known 

 to possess magnetic properties, although in other cases the 

 rust may be quite free from monoxide and yet be magnetic. 



