318 PROCEEDINGS OF SECTION B. 



The powder is still attracted by the magnet when hot, but 

 more strongly on cooling, as in the case of metallic iron. 



M. Sarzeau's' results wei-e confirmed by converting pre- 

 cipitated ferrous carbonate into the acid soluble carbonate by 

 passing carbon dioxide through water containing ferrous 

 carbonate in suspension. On warming this solution or 

 exposing it to the air the carbon dioxide escaped, and a dark 

 coloured precipitate was thrown down. Usually this was 

 found to be attracted by the magnet, but not always. On 

 further warming and longer exposure it gradually acquires a 

 buff colour and becomes magnetic, although not strongly so, 

 but seen by acting upon it with the magnet under water. A 

 temperature of about 70° C. seemed to be the best. At 

 from 270° to 290° C. the colour became red, the magnetic 

 properties being retained even after ignition ; the solution in 

 hydrochloric acid showed no trace of ferrous salt with 

 potassium ferri cyanide. 



There is sometimes a little difficulty in obtaining the 

 magnetic sesquioxide by this process. The cause is not quite 

 clear, but is probably due to the ferrous carbonate not having 

 in all cases been thoroughly washed free from other salts. 



Dr. F. Grace Calvert, in a paper on the " Oxidation of 

 Iron," (Journal Chemical Society ^ 1871, p. 198, and Chemical 

 News, 1871, vol. 23, p. 98), gives the following analysis of 

 rust : — 



Conway Bridge. Llangollen. 



" Iron sesquioxide 93-094 92*900 



Iron protoxide 5-810 6-177 



Iron carbonate -900 -617 



Silica.... -196 -121 



Ammonia - — 



Calcium carbonate — -295" 



No remark is made as to whether the rust was magnetic 

 or not, although it probably was ; and the same remark 

 doubtless applies equally to the rust described by Mr. Cowper 

 and Dr. F. Muck, as follows : — 



" Oxidised Iron from the condenser of H.M.S. Spartan" 



by Richard Cowper, A.R.S.M. (Journal Chemical 



Society, 1882, vol. h., p. 256.) 



The specimen was found in part of the tank of a surface 



condenser, and which in use had been constantly subjected 



to the action of sea water at a temperature not exceeding 



100° F. 



