Dr THOMAS THOMSON on some Experiments on Gold. 27 



had been converted into peroxide, and had, therefore, united 

 with 3 grains of oxygen. I consider it demonstrated, therefore, 

 that peroxide of gold is composed of 



1 atom of gold, 25 



3 atoms of oxygen, 3 



28 



3. I was curious to know the composition of muriate of gold. 

 It was exceedingly probable, from the facts stated in the " At- 

 " tempt," vol. i. p. 440, that muriate of gold is a compound of 

 two atoms muriatic acid, and one atom peroxide of gold. But 

 a direct analysis seemed more satisfactory. It was executed in 

 the following manner. 



Twenty-five grains of pure gold were dissolved in nitro-mu- 

 riatic acid ; the solution was cautiously evaporated, till it as- 

 sumed a brownish-red colour. It was then allowed to cool. 

 When cold, it was solid, had a most disagreeable, astringent, 

 and metallic taste, and possessed the usual corrosive qualities 

 which characterize muriate of gold. It weighed 42'8 grains. 

 When this salt was dissolved in water, a small quantity of mat- 

 ter remained, which had a dirty-greenish colour, was easily re- 

 duced to metallic gold, by the application of the heat of a spi- 

 rit lamp, and weighed, when thus reduced, O8 grain. Thus a 

 quantity of muriate of gold, containing 24.2 grains of gold, 

 weighed 42 grains. 



To determine the quantity of muriatic acid in this salt, it 

 was necessary, in the first place, to get rid of the gold. For, 

 when nitrate of silver is dropt into the undecomposed salt, both 

 the gold and the muriatic acid precipitate along with the silver. 

 I therefore put a clear plate of copper into the solution, and left 

 it till the whole gold had been precipitated in the metallic state. 

 The copper was then precipitated by caustic potash, and after 



D 3 



