Composition of an Acid Oxide of Iron. 



221 



withdrawing it by a tube and mixing with a large quantity of 

 distilled or of lime water (which latter seems to possess the 

 property of checking the rapidity of the decomposition of this 

 potash salt when very dilute), to ascertain whether the subsi- 

 dence of the uncombined oxide of iron was so complete that 

 an apparently inappreciable quantity was held in suspension ; 

 a certain quantity of this clear amethystine solution was trans- 

 ferred to a retort of a known capacity — leaving, of course, a 

 portion of atmospheric air in the upper part of the body and 

 in the neck of the retort ; this quantity of air was accurately 

 determined by previous measurements and graduation of the 

 retort; heat was then applied, and the contents of the retort 

 raised to violent ebullition which was continued so long as 

 any gas was evolved ; these gaseous products were collected 

 over water, and when no more gas was. liberated absorption 

 was allowed to take place by withdrawing the lamp from the 

 retort; any air which the retort then contained was added to 

 that already collected, and when the gas had acquired the 

 temperature of the surrounding atmosphere, it was measured, 

 the known bulk of atmospheric air originally contained in the 

 neck and upper part of the retort subtracted from it, and the 

 residue, oxygen, corrected for temperature and pressure. 



The oxide of iron deposited during the boiling was dis- 

 solved in hydrochloric acid and estimated in the usual way. 

 I subjoin the detail of an analysis as an example*. The results 

 of several successive experiments are contained in the follow- 

 ing table : — 



The mean of these experiments gives 22*27 parts of oxygen 



* A retort filled to a certain limit with the solution left 13*75 cub. in. of 

 atmospheric air in the body and neck of the retort, and gave 26 cub. in. of 

 gas at a temperature of 58°, and barometer at 29-9 26 — 13-75 air== 12-25 

 oxygen corrected, weighs 4-2 grs. The oxide of iron freed from silica by 

 hydrochloric acid and ammonia, gave 16"4 grs. of sesquioxide= 11*48 iron, 

 and 4*92 oxygen + 4-2 = 9* 12 oxygen combined with 11-48 iron. 



