156 Intelligence and Miscellaneous Articles. 



from this that the presence of certain fixed acids is favourable to the 

 combination of alumina with oxide of cobalt. These observations 

 explain the cause of failure which chemists occasionally incur, in 

 attempting to prepare Thenard's blue without employing phosphate 

 or arseniate of cobalt. — L'Institut, Juin 27, 1849. 



DETECTION OF IODINE AND BROMINE. 

 BY M. ALVARO REYNOSO. 



The method employed to ascertain the presence of these bodies, 

 when they exist as iodides or bromides, the author remarks, consists 

 in dissolving them in water, to add starch in the state of paste, or 

 aether and a few drops of solution of chlorine. The chlorine seizes 

 the metal combined with the iodine or bromine, and these bodies 

 colour the starch blue, or dissolve in the aether ; but iodine and 

 bromine having the property of combining directly with chlorine, 

 and of forming a chloride of iodine or of bromine, the chlorine, 

 in order to detect the presence of these bodies, ought not to be em- 

 ployed in excess ; because the chlorides of iodine or bromine are 

 decomposed by contact with water and produce hydrochloric acid, 

 and iodic or bromic acid without acting on the starch or the aether. 



This experiment was very difficult to perform ; often, indeed, 

 these bodies could not be discovered, and this was supposed to be 

 owing to the above-described difficulty. Then the quantity of chlo- 

 rine was diminished, from the fear of exceeding the requisite pro- 

 portions, and it happened that the quantity of chlorine was not suf- 

 ficient to set the iodine at liberty. The manner in which the chlo- 

 rine was employed also increased this error ; in fact, it is well known 

 that a solution of chlorine is weakened by keeping, and that even- 

 tually its power is lost, in spite of every possible precaution. Thus 

 on pouring into a solution of an iodide or bromide a very small 

 quantity of aqueous solution of chlorine, it happened that the iodine 

 was not see free, and that all the chlorine was employed in forming 

 hydrochloric acid. This method, then, was not applicable to the 

 detection of small quantities of iodine or bromine, especially when 

 these bodies are mixed with substances capable of seizing the chlo- 

 rine. It was therefore desirable that the iodine or bromine should 

 be isolated by means of a body incapable of acting upon them, what- 

 ever might be its excess. Oxygenated water fulfills these conditions ; 

 it decomposes hydriodic or hydrobromic acid without at all acting 

 upon the iodine or bromine set free by it. 



The following is the method of proceeding for iodine : a bit of 

 binoxide of barium is to be put into a small glass tube closed at one 

 end ; then are to be added to it distilled water, pure hydrochloric 

 acid, and paste of starch ; the operator is to wait till bubbles arise 

 to the surface, and then the iodide is to be added. A rose-blue 

 colour is immediately procured if the quantity of iodine is but small, 

 but of a deep blue if the quantity of iodine is considerable. 



It is more convenient to operate on these conditions ; not only 

 considering them as manipulations which become very easy, but also 

 with regard to the success of the experiment. On this plan, the 



