22 Dr. Fownes on the Action of Oil of Vitriol 



the crystalline deposit, and the latter washed once or twice 

 by decantation with cold water and then transferred to a 

 paper filter. When the liquid which passes tastes no longer 

 strongly acid and astringent, the filter and its contents may 

 be spread upon a few folds of bibulous paper and placed to 

 dry over a surface of sulphuric acid in the vacuum of the air- 

 pump. 



The acid liquid from which the crystals were deposited, is 

 found on examination to contain in solution peroxide of iron 

 and the sulphates of potash- and ammonia. 



The new substance when dry presents a very beautiful ap- 

 pearance, resembling, as before remarked, thionurate of am- 

 monia ; under the microscope it is seen to consist of small 

 transparent 6-sided tables. It may be heated to above 300° 

 Ft without loss of weight or alteration of any kind ; at a red 

 heat it is slowly decomposed, leaving red oxide of iron with 

 some sulphate of potash. It is, as the mode of preparation 

 shows, insoluble in cold water, nevertheless a lengthened so- 

 journ in contact with that liquid brings about slow decompo- 

 sition ; a little free sulphuric acid prevents this change; hence 

 in preparing the substance, the necessity of avoiding pro- 

 longed washing, even with cold water, as the salt begins to 

 change and grow red as soon as the free acid has been re- 

 moved. With boiling water the change is immediate; the 

 substance assumes the colour of rust, and peroxide of iron is 

 dissolved out. Alkalies decompose it instantly, oxide of iron, 

 retaining the crystalline appearance of the new body itself is 

 separated, and the solution after filtration is found to contain 

 abundance of sulphuric acid. Carbonate of potash with the 

 aid of heat disengages ammonia; the oxide of iron is not in 

 this case separated, but remains in solution, communicating 

 to the alkali a deep red colour ; the addition of water, how- 

 ever, causes the deposition of the oxide. These characters 

 suffice to point out the general nature of the substance under 

 examination. 



A portion carefully dried in vacuo was next subjected to 

 analysis : — 



20 grs. dissolved in hot hydrochloric acid and precipitated 

 by ammonia gave 6 grs. of oxide of iron, and the filtered so- 

 lution, evaporated to dryness and ignited with the usual pre- 

 cautions, afforded 2*9 grs. of sulphate of potash, equivalent to 

 l - 58 grs. of potash. 



20 grs. of the substance, dissolved in hydrochloric acid and 

 precipitated by chloride of barium, gave 34- - 4- grs. of ignited 

 sulphate = 11*8 grs. of sulphuric acid. 



20 grs. of the substance, digested with ammonia and filtered, 



