222 Mr. Denham Smith on the 



by Weights to 28 parts or one equivalent of iron, which is 

 equal to a deficiency of 1'74 part in three equivalents, or 24 

 parts of oxygen. This is, I submit, an approximation suffi- 

 ciently near to three equivalents of oxygen to one of iron, to 

 justify me in adopting the formula FeO 3 , as representing the 

 constitution of this acid oxide of iron ; especially when we 

 consider that the circumstances under which the experiments 

 were made would indicate the probability of some free sesqui- 

 oxide of iron being suspended in the solution, as, from the 

 unstable nature of the compound, a short period of time only 

 could be allowed for the deposition of any insoluble matter, 

 and the impossibility of subjecting it to filtration, owing to its 

 decomposition by the contact of organic substances. This 

 excess of oxide of iron varies in the different experiments 

 quoted, so that whilst Nos. 4, 5, and 6 afford 21 to 22 parts 

 oxygen to an equivalent of iron, 1, 2, 3, and 7 all exceed 22 

 of the gas to an equivalent of the metal, the last, No. 7, espe- 

 cially; and this experiment being the one upon which I am in- 

 clined to place the greatest reliance from the concentrated and 

 clear state of the solution, gives nearly 23 parts (22-85) of 

 oxygen to 28 iron. This cause, together with a certain amount 

 of decomposition during the transference from the vessel in 

 which the solution was made to the retort, affords an expla- 

 nation of the deficiency in the quantity of oxygen as indicated 

 in every experiment, in comparison with that which I theo- 

 retically assign to this compound. 



In no one case was the quantity of oxygen actually obtained 

 so small as to indicate a compound of 20 parts of oxygen to 

 28 of iron (2 Fe + 50 or F 2 + O 2 ), and I do not consider the 

 formula intermediate with this last and the constitution I 

 have assigned to the oxide, is a very probable one to exist, 

 being 3 F-f-8 O; moreover, in four out of seven experiments 

 more oxygen was obtained than such a compound could 

 evolve. 



The conclusion at which I arrived, that this ferric acid is 

 a teroxide of iron, is confirmed by the subsequent examina- 

 tion of the insoluble crimson compound it forms with barytes. 

 This salt is readily formed by adding an excess of a dilute so- 

 lution of a barytic salt to the clear amethystine solution, 

 which, prepared as I have described and dissolved in close 

 vessels, will not contain the sulphates in any marked quantity, 

 nor any carbonic acid whatever, the precipitate being washed 

 in vessels excluded from the atmosphere with freshly boiled 

 distilled water, to prevent the access of carbonic acid to the 

 alkaline solution, and drying at 212° F. It is of a dark crim- 

 son red colour, decomposable before drying by the mineral 



