62 PROCEEDINGS OF THE AMERICAN ACADEMY 



of the recorded analyses of ancient silver coins to which we have had 

 access have we been able to find that any one has detected so large 

 an amount of lead in these coins, as we have shown to occur in Ameri- 

 can fine silver of the year 1860, if we except a single analysis by 

 Professor Draper, who found neai'ly 3 per cent of lead in a silver 

 coin of Hadrian. The greatest percentage of lead observed by Briiel 

 (the author of the remark just quoted) was only 0.12. It is probable, 

 however, that the methods of analysis — none of which are recorded 

 — employed for separating lead from silver by the chemists to whose 

 labors we have referred, were less delicate than the process which we 

 have ourselves made use of. 



It is interesting also in this connection to observe, that the Ameri- 

 can system of amalgamation, which at one time — before its peculiar 

 fitness for the circumstances of the case in which it is employed had 

 been recognized — was so frequently criticised by European metal- 

 lurgists, affords silver which is less strongly contaminated with lead, 

 and is probably purer in other respects, than is produced by any other 

 process of manufacture. 



11. On the extreme Difficulty of Re7noving the last Traces 

 of Carbonic Acid from large Quantities of Air. 



In the course of our research upon the impurities of zinc, we insti- 

 tuted a series of experiments, in order to ascertain whether the dis- 

 agreeable odor of hydrogen gas, as generated from common zinc by 

 means of sulphuric acid, could be attributed to the presence of any 

 gaseous compound of carbon, — an apocryphal doctrine which seems 

 to be quite generally credited. 



The results of these experiments were entirely negative, in so far as 

 they related to the point in question, and we should not have thought 

 of publishing them, had it not been proved to us, by a memoir recently 

 printed in Poggendorff*'s Annalen, that one of the phenomena Avhich 

 we then observed had not been sufficiently dwelt upon by chemists. 



In our experiments above referred to, a jet of hydrogen was burned 

 in a glass globe thirty centimetres in diameter, through which was 

 drawn, by means of an aspirator, a steady current of air. Before 

 entering the globe, this air had passed through an apparatus, described 

 in full below, which was intended to deprive it of all its carbonic acid, 

 and on leaving the globe it was drawn through a bottle containing 



