Contribution towards the assaying of Coins. 257 



consequence of these observations I made my docimasllc 

 researches in the following manner: 



1st. After freeing the coin from its ruit, the ceriigo nolilisy 

 I poured over it in a phial moderately strong nitric acid, and 

 left it to spontaneous solution. Next day 1 poured the so- 

 lution from the remaining part of the coin, and, having 

 supplied its place by a new quantity of acid, repeated the 

 5ame process till the coin was completely dissolved. 



If it contained tin, which was the case with all the Greek 

 coins, but only with some of the Romany it remained be- 

 hind in the form' of a grayish white calx, and was collected 

 on filtering paper. In regard to Roman coins which con- 

 tained no tin, its absence was indicated by the perfect clear- 

 ness of the nitric solution. A counter-experiment, in which 

 I employed a mixture of copper with a quantity of tin ex- 

 actly weighed, showed that 100 parts of the above calx of 

 tin might be estimated as equal to 7 H parts of metallic tin. 

 In order that I might convert the calx of tin separated from 

 the coin into a metallic form, I boiled it with a quantity of 

 muriatic acid sufficient for its solution, diluted the solution 

 with two parts of water, and immersed in it a rod of zinc, 

 by which means the metallic tin was precipitated. 



But when the solution of copper containing tin was de- 

 composed by nitric acid, the calx of tin was by these means 

 combined with a greater proportion of oxygen, and thereby 

 rendered unsusceptible of solution in muriatic acid. In this 

 case I found the diy way more convenient, and eflected the 

 revivification of the metal in a well-closed charcoal crucible 

 over a stroi^g fire maintained by a pair of bellows. Of the 

 gold supposed to be contained in the earlier antient coins, 

 and which must have been found as a residuum in the nitric 

 solution, I could discover no traces. 



2d. I first examined the nitric solution which contained 

 no tin, to find whetlier it contained silver. I mixed a por- 

 tion of it with a saturated solution of nmriate of soda^ and 

 put into another a plate of copper which I had weighed : 1, 

 however, found no certain traces of that metal, except in a 

 coin of the Mamertlnes. 



3d. To effect a separation of the lead, I decomposed the 

 nitric solution with a saturated solution 'of sulphate of soda, 

 collected the sulphate of lead separated from the mixture, 

 reduced to a small quantity by evaporation, and either re- 

 duced it hx a crucil)le with charred tartar, or calculated the 

 quantity by counter-experiments. According to which, 

 100 parts of sulphate of lead might be estimated as equal 

 to 7o part? of metallic lead. 



Vox.. XVII, No. ()7. R lefllctod 



