by Weight and by Volume. 207 



estimated without further manipulation in presence of all other 

 - metals or earths. In systematic analysis we should have to deal 

 with lead only. I have found three methods available for the 

 separation of lead and baryta from bismuth. 



I. Add to the solution containing, amongst other substances, 

 lead, bismuth, and baryta, dilute sulphuric acid in excess. Sul- 

 phates of baryta and lead will precipitate, the mixture is filtered 

 and the insoluble sulphates drenched with water. The filtrate 

 which contains the bismuth in solution as soluble sulphate is 

 evaporated to expel excess of acid, bichromate of potash is added 

 in excess, and the experiment proceeded with as above. 



II. If necessary, add a slight excess of nitric acid to the solu- 

 tion containing lead, bismuth, baryta, &c., and precipitate with 

 bichromate of potash ; on filtering, baryta will remain in solution 

 soluble in nitric acid. The precipitated chromates of lead and 

 bismuth are now treated with caustic potash of spec. grav. 1'33. 

 Chromate of lead is readily and completely dissolved by caustic 

 alkali, while chromate of bismuth is comparatively insoluble. By 

 treating the chromates of lead and bismuth with potash, there- 

 fore, we obtain the lead chromate in solution, and by filtration 

 separate it from the bismuth chromate which is insoluble. From 

 the amount of chromate of bismuth obtained, the metal is cal- 

 culated as in I. 



III. That oxalic acid and neutral oxalates, on addition to so- 

 lutions of bismuth, precipitate oxalate of bismuth, is a fact long 

 known. On adding an excess of oxalic acid with a slight ele- 

 vation of temperature, I have observed that the precipitate pro- 

 duced on the first addition of acid is readily redissolved. This 

 circumstance has not hitherto been noticed, I believe. Oxalate 

 of lead is completely insoluble in excess of acid, even in a hot 

 solution. If, therefore, we supersaturate a solution containing 

 lead and bismuth with oxalic acid, and heat to ebullition, the 

 bismuth remains in solution, while the lead remains as an inso- 

 luble compound. By means of oxalic acid, I find that lead and 

 bismuth may be separated with facility and accuracy. 



Of these three methods the first is generally applicable, espe- 

 cially when the bismuth alone is to be estimated. The second 

 method is particularly adapted when the lead or baryta are to be 

 estimated also. The third process enables us to separate lead 

 and bismuth with great accuracy. Circumstances will suggest 

 a preference. 



Separation of Cadmium from Bismuth. — These two metals when 

 associated cannot be separated by any known method with facility. 

 By the use of bichromate of potash, bismuth may be precipitated 

 perfectly free from cadmium when the two metals are in so- 

 lution. 



