for some Pure Metals. 225 



Metals Used. 



Lead. — This was very pure, and was specially prepared for 

 me by the method of Stas, by Mr. N. T. M. Wilsmore, 

 M.Sc, F.C.S. Lead acetate was dissolved in water and 

 digested for a week with sheet lead. The solution was 

 filtered into hot dilute sulphuric acid, and the precipitated 

 sulphate treated with water, dilute sulphuric acid, and again 

 with water till perfectly free from acid. The sulphate was 

 then stirred for some days in a beaker with solution of large 

 excess of ammonium sesquicarbonate and ammonia, and washed 

 till free from soluble ammonium sulphate. This treatment 

 was repeated till the lead sulphate was nearly all converted 

 into carbonate. A little of this was converted into monoxide 

 by heating in a platinum dish, and the remainder nearly dis- 

 solved in dilute nitric acid, and the oxide added little by little, 

 thus precipitating any iron which might be present. The 

 solution was again filtered and added to solution of excess of 

 pure ammonium sesquicarbonate and stirred, thus forming 

 pure lead carbonate. This was dried and reduced under 

 potassium cyanide in an unglazed porcelain crucible, the 

 contents of which were poured into a polished steel mould. 

 The lead button was washed with water, alcohol, and ether, 

 and immediately placed in a glass tube with a narrow tube 

 sealed on to the end. This was alternately exhausted and 

 filled with pure hydrogen about a dozen times, and finally 

 exhausted with a Sprengel and hermetically sealed. The 

 lead was again melted and run into the narrow tube, a com- 

 pact rod being thus obtained, which was drawn through 

 draw-plates down to a wire of the desired size. All the 

 reagents used were as pure as could be obtained, and were 

 tested for impurities, especially metallic impurities, and when 

 necessary were repurified. Mr. Wilsmore considered that 

 the lead was free from all other metals, and from impurities 

 of all kinds except perhaps a- trace of oxide formed during the 

 washing in water. 



Silver. — This was prepared by Mr. W. Percy Wilkinson, 

 Government Analyst, and considered by him to be " fairly 

 pure."" Silver chloride was reduced with wood charcoal and 

 pure sodium carbonate. The ingot was washed with boiling 

 water slightly acidulated with hydrochloric acid, and finally 

 scrubbed with clean sand. This was re-dissolved in pure 

 nitric acid, largely diluted, precipitated with dilute hydro- 

 chloric acid, washed with water, boiled with nitric acid, 



