280 Atomic Weights of Iodine and Bromine. 



the whole became transparent, the liquor (about 12 ounces) 

 still continuing saturated with chlorine; but bleaching sud- 

 denly, when, on commencing the evaporation, it reached about 

 150°. Towards the end, about a drachm of nitric acid was 

 added to insure complete oxidation ; but no red fumes ap- 

 peared. The acid heated red for a quarter of an hour weighed 

 29*25 grains. Yielding to the nail when cold, it still appeared 

 to contain water ; but as a small portion of black scum lay on 

 a part of the surface, the ignition was not repeated for fear of 

 decomposition. This black substance being separated on 

 dissolving the acid, was too small to weigh. The acid dis- 

 solved in distilled water, and cautiously neutralized with bi- 

 carbonate of potassa, keeping it warm to dispel the carbonic 

 acid, was precipitated with nitrate of lead in excess. The pre- 

 cipitate was boiled in weak acetic acid, and continued digest- 

 ing in it twenty-four hours, to get rid of the excess of base so 

 constantly tantalizing in precipitated phosphates, and to show 

 the exact quantity of acid produced. In this I failed, the pre- 

 cipitated still weighing, after heating red, 130*7 grains. The 

 experiment is, however, sufficient to prove that 12*05 grains 

 of phosphorus require less than 17*2 of oxygen to form the 

 phosphoric acid of 4*5, (for if the acid thus formed had been 

 that of 3*5, the precipitate must have weighed at least 141*25 

 grains,) and 16*2 of oxygen is exactly the quantity to corre- 

 spond with Sir H. Davy's experiment, by which 12*05 grains 

 of phosphorus would produce 28*25 of phosphoric acid. The 

 views of Berzelius on the phosphates appear to me correct, 

 and the acid of 3*5 still a problem. 



The new experiments of Berzelius quoted in the Quarterly 

 Journal for September, seem to prove that the atomic weights 

 of iodine and bromine have been deduced from materials not 

 free from chlorine ; and he makes them 



iodine 789*145 bromine 489*15 



or x2 by the English system ... 1578*290 978*30 



But as he makes chlorine 221 '325, which x 2 = 442*650, and 

 as the above numbers were obtained by comparison with 

 chlorine, if the true number for that substance is nearer 4*5, 

 iodine will turn out 16*04, and bromine nearly 9.95 ; numbers 

 as near to 16* and 10* as the nature of the experiments would 

 admit, and approaching, in the case of iodine, to the result of 

 former experiments by Gay-Lussac and Prout. 



I am, Gentlemen, yours, &c. 



Plymouth, March 8, 1830. JoHN PrideauX. 



XL. Account 



