464 



he says, certain marks of zinc. This may possibly have been 

 the case in Bishop Watson's particular specimen, but the celts 

 examined by other chemists proved destitute of zinc, and its 

 introduction into the ancient bronzes must have been a very 

 rare practice. Zinc would no doubt enhance the colour, and 

 increase the malleability of the compound, but it would lessen 

 its hardness, one of the chief qualities for which the metal was 

 valued. Add to this, the test assigned of the presence of zinc 

 is equivocal. Dr. Pearson observed a fume, to a small amount, 

 when portions of an ancient bronze, which he proved not to 

 contain zinc, were strongly heated ; and he quotes the state- 

 ments of certain assayers, who observed fumes to arise from 

 charges of lead with silver, or lead with gold and silver, when 

 much air is admitted. He also says that ' if much air be ad- 

 mitted to the alloy of copper with tin in fusion, a white smoke 

 will sometimes be seen.' 



" The specific gravity of the celt was 8*767, an indication 

 of the presence of tin, and of the absence of zinc ; but to de- 

 termine the question the following process was adopted : 



" A portion of the metal was dissolved by heat in nitric 

 acid ; a white powder separated, which, being edulcorated, 

 dried, and mixed with borax and incinerated pitch, was exposed 

 to the heat of a Russian furnace. The black mass obtained 

 from the crucible, when viewed with a strong magnifier, dis- 

 closed thousands of metallic particles disseminated through it. 

 By pulverizing and washing this matter, I obtained a portion 

 of the metal : its solution in muriatic acid, mixed with a small 

 quantity of nitric acid, afforded those appearances with solution 

 of gold which indicate tin. The nitric solution of the celt, 

 from which tin had been thus separated, was subjected to the 

 action of a bright plate of lead immersed in it ; the whole of 

 the copper was thus precipitated, as was proved by the test 

 of ammonia. The filtered liquor, now deprived of copper and 

 tin, was mixed with solution of sulphate of soda, and boiled 



