270 OXIDATIONS OF IRON. 



by a siphon, which is the surer way; and a few drops of 

 water be afterward added, to take up the alkali, that ad- 

 heres to the surface of the precipitate and the sides of the 

 glass ; a mass of sulphate of iron will remain, gveat part of 

 which will dissolve in water, and exhibit all the properties 

 I have just mentioned. I have left this precipitate for 

 twenty-four hours macerating in potash, and at the expira* 

 tion of that time have still obtained soluble sulphate of 

 iron. 

 Ammonia In a concentrated solution of ammonia, the result is still 



more* striking- mo;e striking; because, as the density of the precipitated 

 ly. sulphate of iron greatly exceeds that of the ammonia, the 



precipitate falls quite to the bottom of the glass, and great 

 part of it sticking to this, escapes the subsequent action of 

 the alkali ; which does not happen with the concentrated 

 fixed alkalis, the density of which is greater t! an that of 

 the ammonia, and in consequence they envelope it on all 

 sides. 

 Why a gveen This is the reason why these solutions, which when con»> 

 throwndown cen trated throw down a white precipitate, throw down a 

 green precipitate when they are diluted with water freed 

 from air by long boiling. For this reason, limewater never 

 gives a white precipitate, even with the most concentrated 

 solutions. Lastly, for this reason I suspected before hand, 

 that the muriates and nitrates, which give white precipitates 

 with the alkalis, would be precipitated green by barytes 

 Not from addi- and strontian water, which in fact is always the case. T^e 

 poiiu 9 % l & m ' green colour cannot be attributed to a superoxidation occa- 

 sioned by the air in the lime, barytes, or strontian water; 

 for, beside that the rapidity of the operation, and the quan- 

 tity of air that so small a bulk of distilled water could con- 

 tain, would not justify such an idea, 1 took the precaution 

 to boi! the water in which I dissolved the three earths for an, 

 ]ipur, and half, 

 The same If di- If, instead of diluting the solution with water, it be di- 

 ' ute ^ evenw ?'° luted with sulphuretted hidrofifen, in which the ra-esence of 



m I pn i netted n ^ i 



n, oxigen cannot be suspected, the result will be still the same ; 

 the precipitates formed by alkalis will be green or black, 

 and never white. It is true Mr. Thenard says', that, on pour- 

 ing sulphuretted hidrogen on a red solution of iron, this will 



yield 



