REPORT Oy MINERAL AND THERMAL WATERS. 51 



and bromine come over together, Osann proposes to stop the 

 distillation, exactly at the point at Avhicli the precipitate is an 

 equal mixtiu-e of the two acids. The deficiency of bromine in 

 the solution is thus compensated for by the chlorine obtained. 

 It is evident, however, that a very practised eye would be re- 

 quired, in order to obtain correct quantitative results by such 

 a method as the above. 



The same author proposes to separate iodine from chlorine, 

 by causing the mixture to pass over in a state of vapour into a 

 solution of potass, and then precipitating it with arsenious acid 

 or arseniate of ammonia. 



The iodine unites with the arsenic, which latter is precipi- 

 tated by sulphuretted hydrogen. This being got rid of by 

 oxide of lead, the iodine is obtained by uniting it with silver. 



Henry Rose * has proposed a new method of distinguishing Oxides of 

 between the protoxide and peroxide of iron. """"• 



When muriatic acid is added to a mixture containing both 

 these oxides, the protoxide is converted into a protochloride, the 

 peroxide into a perchloride. 



Now metallic silver robs the latter of its half-atom of chlorine, 

 converting it into the protochloride, and hence the increase of 

 weight in the silver added, enables us to calculate the amount of 

 peroxide of iron originally present. 



Another method for the same object has been proposed by 

 Fuchs f. It consists in digesting the solution of protoxide and 

 peroxide in an acid, with carbonate of lime or of magnesia, by 

 either of which the peroxide is precipitated, whilst the protoxide 

 remains untouched. 



This peroxide is obtained in a state of mixture with the earth 

 and acid employed, and must be separated from both by the 

 ordinary means. 



The only difficulty consists, in preventing the weight of the 

 precipitate from being increased during filtration, in consequence 

 of the conversion of some of the protoxide into peroxide. 



In order to prevent this as much as possible, the precipitate 

 should be washed repeatedly with warm water, before the super- 

 natant liquor is thrown upon the filter. 



For the detection of organic matter in mineral waters, Dr. Organic 

 Davy has suggested the employment of a solution of nitrate of ""'"'er. 

 silver J. The blackening, which usually takes place in this fluid 

 upon exposure to light, is attributable to the presence of organic 

 matter ; for if care be taken to purify the water, light produccb 

 no change. 



* Berzelius, Jahresberichf, 1832, p. 164. 

 t Jahiesbericht. 1832, p. lG4. 

 X Edinburgh New Phil. Journal, 1828, p. 129. 

 E 2 



