24-G Chemistry. [Lecture 32. 



sheet of tin is immersed in a solution of gold, 

 the oxide of gold is precipitated of a purple co- 

 lour, and when scraped off forms the beautiful 

 purple powder of Gassius much employed in 

 enamelling. 



2d. Platinum was not known as a distinct 

 metal before the year 1752. Its specific gravity, 

 when pure, exceeds that of gold, and it is there- 

 fore the heaviest substance in nature. In duc- 

 tility and malleability it is far inferior to gold : 

 as it is also the most infusible of metals, it is be- 

 come of the most material use to chemists, in 

 forming crucibles and other vessels which can 

 endure the strongest heat of a common furnace, 

 as well as the action of all simple acids, without 

 injury. It seems, however, not capable of a high 

 polish, and its dull white colour will probably 

 prevent its use as an ornamental metal. 



Platinum unites well with iron: and I have 

 heard that the Spaniards find it of great im- 

 portance, combined with iron, in the manu- 

 facture of musket barrels, which it preserves 

 from rust (for, like gold, it cannot be oxidized 

 by any ordinary means), and at the same time 

 it gives them additional strength and tenacity. 



3d. Silver, in beauty, scarcity, and malleabi- 

 lity, ranks next to gold. Its uses in the arts and 

 in commerce are well known. In medicine and 

 chemistry it is of considerable importance. Dis- 

 solved in nitric acid, it serves the chemist as a 

 test to detect the smallest quantity of muriatic 

 acid contained in any fluid. For as it forms 



