206 Mr. R. W. Pearson on the Determination of Bismuth 



tity of well-washed chroraate of bismuth in these liquors for 

 twelve hours with frequent agitation of the mixture. To deter- 

 mine the quantity of bismuth dissolved from the tints produced 

 in the several solutions by sulphuretted hydrogen, I prepared 

 dilute standard solutions of nitrate of bismuth, containing re- 

 spectively known quantities of metallic bismuth. Through 

 each of these solutions I passed sulphuretted hydrogen gas, and 

 in this M'ay obtained " comparison tests " of bismuth. When 

 examined by this method I found the following to be the — 



Per-centage Solubility of Chromate of Bismuth in water , acetic 

 add, nitric acid, and potash. 



In nitric acid, In potash, 

 .' In water. In acetic acid. sp. gr. 1'03. sp. gr. r33. 



Chromate of bismuth -00008 -00021 -00024 -00016 



I found by experiment that the following reaction takes place 

 with bichromate of potash and nitrate of bismuth : — 



70,000dth gr. of bismuth : precipitate immediate. 

 lOOjOOOdth ... opalescence produced. 



150,000dth .#. reaction ceases. 



The characteristic colour of chromic acid is possessed in a 

 remarkable degree by the chromates of potash. Thompson 

 states that one part of chromate of potash may be recognized in 

 40,000 parts of water. I found that bichromate of potash, when 

 diluted 70,000 times, may be detected by its yellow colour. 



Estimation of Bismuth by Weight. 



Previous to precipitating the bismuth in solution, as chromate, 

 it is necessary, as when precipitating by carbonate of ammonia, 

 to ascertain the absence of lead. This may be effected, and, if 

 present, its removal accomplished, by processes to be indicated 

 further on. Nitric acid is the most convenient solvent for ores, 

 &c. of bismuth, taking care to remove any large excess of acid 

 in solution by evaporation. In the absence of lead the solution 

 is supersaturated with bichromate of potash, and the mixture 

 warmed to aggregate the precipitate, which is collected upon a 

 filter and thoroughly washed with water. When washed, the 

 precipitate and filter are di-ied. The chromate of bismuth may 

 now be estimated after combustion of the filter, or weighed in a 

 filter of known weight ; deducting the latter from the total ob- 

 tained, 1 grain of bismuth is contained in 1 '49074 gi-ain of the 

 chromate of the oxide. 



Separation of Bismuth from Lead and Baryta. — I include 

 baryta, since on the removal of lead and baryta, bismuth may be 



