Intelligence and Miscellaneous Articles. 325 



When sufficient chlorine has been added to decompose the whole 

 of the alkaline bromide, the paper immersed is not immediately- 

 coloured, for then the iodine exists in the liquor in the state of bro- 

 mide, and no longer acts upon the starch ; but this remarkable cir- 

 cumstance occurs, that the paper being withdrawn from the liquor 

 and exposed to the air, the moistened part assumes a reddish tint in 

 about two minutes, then becomes violet, and afterwards blue; the 

 same reaction occurs, but in a longer time, when the starched paper 

 is left to macerate in the liquor. 



This effect, unquestionably owing to the decomposition of the 

 bromide of iodine by the organic matter of the paper, or perhaps 

 even of the starch itself, admits of detecting minute quantities of 

 iodine in the alkaline bromides. — Journal de Chim. Medicate, Sep- 

 tembre 1842. 



PREPARATION OF FERROCYANIC ACID. BY M. POSSELT. 



This acid, now sometimes also termed hydroferrocyanic acid, was 

 discovered by Porret, and called by him ferrochyazic acid. According 

 to M.Posselt the following is an improved process for obtaining it : — 

 agitate with aether a concentrated aqueous solution of ferrocyanic 

 acid as obtained by the decomposition of ferrocyanide of lead by 

 means of sulphuric or hydrosulphuric acid, the acid separates imme- 

 diately and may be obtained by filtration ; this remarkable separa- 

 tion of the acid from the water which holds it in solution, requires 

 but little aether. If the solution is moderately concentrated, the 

 whole forms a thick mass by agitation, and after some time the fer- 

 rocyanic acid suspended in the aether, separates from the water sa- 

 turated with aether, and swims on the surface. The water is to be 

 removed by a pipette ; the thick mass is to be put on a filter and 

 washed repeatedly with a mixture of alcohol and aether, containing 

 a considerable portion of the latter ; it is then to be passed between 

 folds of absorbent paper to remove the moisture, and afterwards to be 

 perfectly dried over sulphuric acid in the air-pump. 



In order to avoid preparing ferrocyanide of lead and the aqueous 

 solution of ferrocyanic acid, a concentrated solution of ferrocy- 

 anide of potassium may be prepared in boiled water, and it is to 

 be allowed to cool, entirely excluded from the air ; it is then to 'be 

 mixed with an excess of hydrochloric acid, also deprived of air, and 

 this mixture is to be shaken with aether in the manner described. 

 The acid separates in the same manner, and is to be dissolved in al- 

 cohol, to which a little sulphuric acid is to be added to combine 

 with the potash which it may still contain ; the liquor is to be filter- 

 ed if it is not clear, and this alcoholic solution is to be agitated 

 with aether ; this again separates the acid, which is to be dried as 

 before described. 



This substance possesses all the properties of an acid, and presents 

 a complete analogy with other hydracids. It has a very sour taste, 

 an acid reaction, decomposing the carbonates with effervescence ; it 

 also decomposes with the greatest facility the acetates, tartrates and 



