OXIDATIONS OF IRON. 275 



experiment with two equal quantities of distilled water, from 

 ftne of which the air was completely expelled, while the other 

 was saturated with it artificially, and the results were the 

 same with both. If the crystals of sulphate I used were white, 

 no deposition took place; but if they were green, a precipitate 

 fell down, which was equally bulky in both solutions : so 

 that Scheele's process is calculated rather to show the aci- 

 dity of the green salts of iron to a certain point, than the 

 quantity of air in the water. 



It may be objected to me, that, from the experiments of The quantity 

 Dr, Carradori, boiled water always retains a little air: but, ^ ^^£* 

 beside that I have lately repeated the experiment with water mustbefartoo 

 freed from air by Dr. Carradori's method with the saine™^^ 

 success, the experiments of Henry*, Humboldt, Gay Lus- 

 sac, and more especially of Daltonf , on the absorption of 

 gasses by water, completely terminate the controversy. Ac- 

 cording to Dalton, to whom I refer because he more directly 

 turned his attention to this point, water saturated with at- 

 mospheric- air contains only 2*01-2 per cent of its bulk, of 

 which *778 are oxigen gas, and 1*234 nitrogen. Conse- 

 quently 100 ci^bic inches of water contain about 4- of an inch 

 of pxigen. Now if we consider, that the greater part of this 

 gas is expelled by boiling; and if besides we make a correc- 

 tion for the heterogeneous substances, which according to 

 Lambert and Saussure the air always contains, we shall rind 

 the influence of the oxigen contained in the water, even sup- 

 posing it saturated with it, must be nothing; for if a green 

 salt of iron with excess of oxide be thrown into 100 cubic 

 inches of water at 60° [l6?° F.], a precipitate of at least 15 

 or 20 grains of red oxide will be formed, which cannotbe 

 attributed to the oxigen of the air contained in the water, un- 

 less the experiments of the learned natural philosophers I 

 have quoted be altogether futile. 



Beside this experiment; beside the ammoniacal solution Proofs that the 

 of green sulphate, which passes to red without the possibi- oxigeiiate°so- 

 lity of suspecting the presence of oxigen ; beside the precipi- lutions of iror. 

 tate, which did not increase its oxigenation 1 per cent by 



* Philosophical Transactions for 1803, or our Journal, Vol V. p. 220. 

 J j- Manchester Mem. N, S. Vol. I, "Journal. Vol. XIII. p. 291. 



exposure 



