Intelligence and Miscellaneous Articles. 157 



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oxalate. The salts of chromium however behave differently towards 

 ammonia, which does not throw down the oxide of chromium, even 

 when the barytes has been separated by sulphuric acid. 



The iron salts are decomposed by the solar rays, with an abundant 

 disengagement of carbonic acid, even when the crystals are dry. 



I shall conclude this summary of my investigations by drawing 

 attention to the importance of these salts in analysis ; the more so a* 

 it was with this view I undertook them. 



I think that I have succeeded in explaining the fact, long 9ince 

 known, of the solubility of the oxalate of lime in solutions of the 

 sesquioxides. Iron, aluminum and chromium are always separated 

 from their ores as sesquioxides ; lime and strontia, in the state of 

 oxalates; but we know that lime cannot be separated from the solu- 

 tion of the sesquioxide ; this circumstance is owing to the formation 

 of a double salt, of which the oxalate of lime forms a part. It is 

 therefore necessary to precipitate the sesquioxide by ammonia, which 

 leaves the lime free in the solution, and it is therefore difficult to pre- 

 vent its being thrown down by the carbonic acid of the atmosphere, 

 and thus affecting the weight of the sesquioxide. 



It is especially in the case of alumina and oxide of chromium, 

 that the error may be the greatest. This difficulty is easily avoided 

 by the following process : — I will select as an instance a mineral con- 

 taining iron and lime. It is dissolved in hydrochloric acid ; then 

 a suitable quantity of oxalic acid added, which, if the liquor is diluted, 

 will not produce any precipitate; I now add some oxalate of am- 

 monia in excess, which will precipitate the whole of the lime, which 

 is separated by filtration, oxide of iron remaining in solution entirely 

 free from lime ; this is precipitated, in the ordinary manner, by am- 

 monia. — Comptes Rendus, Nov. 17, 1845. 



REACTION FOR THE DISCOVERY OF SULPHUROUS ACID. 

 BY M. HEINTZ. 



The substance to be examined, dissolved in water or hydrochloric 

 acid, is to be heated with a solution of protochloride of tin in dilute 

 hydrochloric acid to ebullition. If the liquid contains much sulphu- 

 rous acid, sulphuret of tin is precipitated ; but if the quantity be 

 small, no precipitation occurs ; the liquid becomes yellow and ex- 

 hales the odour of sulphuretted hydrogen. It is then requisite only 

 to add a few drops of solution of sulphate of copper to obtain an 

 immediate precipitate of the brown sulphuret of this metal. 



This method of detecting sulphurous acid, it will be observed, is 

 merely a modification of that proposed more than fifty years ago by 

 Pelletier, and since recommended by M. Gerard. 



It is preferable to the process of MM. Fordos and Gelis, which is 

 based on the formation of sulphuretted hydrogen by the contact of 

 metallic zinc and sulphurous gas, inasmuch as it does not require 

 the use of an apparatus to disengage the gas. — Journ. de Pharm. et 

 de Ch., Janvier 1846. 



