Composition of an Acid Oxide of Iron. 223 



acids, including carbonic acid, but less readily by sulphuric 

 acid than by the others. When strongly heated it evolves 

 water and oxygen gas. As diluted nitric acid appeared to de- 

 compose this salt without the formation and evolution of any 

 but oxygen gas, I selected this acid as the agent of analysis. 



Having procured a very thin light flask with a long narrow 

 neck of the capacity of about four fluid ounces, it was about 

 half filled with dilute nitric acid, which, together with the 

 flask, weighed 1862'05grs., to this 33*16 grs. of the red bary- 

 tic salt were gradually added, a rapid evolution of oxygen en- 

 sued with every addition of the barytic ferrate; at the expira- 

 tion of twenty-four hours the flask and contents were weighed 

 = 1891*94' grs., which indicates a loss of 3*27 grs. of oxygen 

 gas ; the solution was of a light pink colour, showing that 

 decomposition was not wholly effected; but this entirely dis- 

 appeared, and the solution became colourless on the addition 

 of two drops of weak hydrochloric acid to the warm solution, 

 evidencing so small an amount of the undecomposed salt as 

 not to be worth considering : this solution evaporated to dry- 

 ness, redissolved, and filtered, gave 2*78 grs. of silica and sul- 

 phate of barytes. On the addition of sulphate of soda to the 

 solution sulphate of barytes was precipitated, which, washed, 

 dried and ignited, weighed, exclusive of ash of filter, 24*64 

 grs.; the oxide of iron precipitated by ammonia gave 8*88 

 grs., leaving 2 "09 for water and loss. 



A second experiment upon a portion of this salt, prepared 

 at a subsequent period to that used in the first experiment, 

 and adapting a tube containing chloride of calcium to the 

 flask, gave from 47*47 grs. of the compound, 4*31 grs. of oxy- 

 gen, and, exclusive of ash of filters, 0'48 grs. of silica, &c, 

 37*82 grs. sulphate of barytes, and 15*27 grs. of sesquioxide 

 of iron, leaving 2*63 grs. for water and loss. 



A third experiment gave 3*06 grs. oxygen, *69 grs. of silica, 

 &c, 27*163 grs. sulphate of barytes, and 10*86 of oxide of iron 

 from 34*47 grs. of the red barytic salt. 



To obtain the water, I merely heated the ferrate gradually 

 and gently on a sand heat till it assumed a greenish colour, 

 rejecting those experiments which were partially converted 

 into a light drab colour, which is an evidence of loss of oxy- 

 gen. 64*48 grs. of ferrate lost 4*93 grs., and 44*41 lost 2*91 

 grs. ; by ignition this green residue was converted into a drab- 

 coloured powder, apparently with the loss of half an equiva- 

 lent of oxygen, which residue, treated with dilute nitric acid, 

 evolved oxygen gas. Now, estimating the loss sustained in 

 these experiments as water and taking the mean, ferrate of 

 barytes when pure will contain 7'2 per cent, of water, and 



