58 PROCEEDINGS OF THE AMERICAN ACADEMY 



of silver,* which precipitate is in enormous mass as compared with 

 the amount of chloinde of lead ; and again, the first precipitate of 

 sulphate of lead, mixed with gold, which is obtained after evaporation 

 with sulphuric acid, occurs in so finely divided a state, that it is exceed- 

 ingly difficult to prevent loss by the passing of a portion of it through 

 the pores of the filter upon which the precipitate is collected. To one 

 unused to the process, it might seem as if the last traces of sulphuric 

 acid could hardly be removed from this precipitate by washing with 

 alcohol. We have satisfied -ourselves, however, that this is easily 

 effected, and that this seeming source of error is, in reality, entirely 

 insignificant ; at any rate, the results given in columns (a), (b), and (c) 

 are in no way influenced by this imaginary error. It may not be 

 amiss to observe, that we have been particularly scrupulous with regard 

 to the treatment of the above-mentioned precipitate, having in every 

 instance continued to wash it with alcohol long after any reaction of 

 sulphuric acid could be detected. It should also here be stated, that 

 the results in which we ourselves place the most confidence are those 

 obtained by determining the amount of sulphuric acid in the mixed pre- 

 cipitate of sulphate of lead and gold (see cols. (3), (4), and (5) of the 

 table), for columns (a), (b), and (c) contain the results of a secondary 

 process liable to all the accumulated errors of a long series of opera- 

 tions ; moreover, the final precipitate of sulphate of lead is very finely 

 divided, and, like the first precipitate, liable to pass through the pores 

 of the filter, as has been previously explained. This second series of 

 experiments has been carried out, not from any expectation that the 

 results would closely agree with those of the first series, but merely to 

 control the latter to a certain extent, and to remove any objection 

 which might be made to the indirect method by which they were 

 obtained. Since the possible inaccuracies of the process tend to a loss 

 of lead, we are confident that the amounts of lead we have obtained 

 are in no instance greater than those really existing in the coin. 



The precipitates of pure sulphate of lead (column (a) of the table) 

 were, in every instance, reduced on charcoal with carbonate of soda, 

 and the button of lead obtained carefully tested for silver, of which 

 none could be detected in any case ; nor did the metal exhibit any 

 reactions, other than those of pure lead. 



The residue of gold and filter paper left after dissolving the car- 



* Compare Mulder, op. cit., p. 217. 



