Improvements in Science. 303 



wards burnished ; their weight is diminished about ^. 

 The sauce takes up some copper, silver, and -a certain 

 quantity of gold ; it is preserved for the purpose of extract- 

 ing these metals. After it has been used, it takes the name 

 of colour water. When allowed to stand at rest, it becomes 

 limped, and a white deposit separates, called deposit of the 

 colour waters, and the supernatant liquor is termed clear 

 waters. Sulphate of iron is added to the clear waters, and 

 then bars of iron are plunged into them. A precipitate 

 containing gold falls down, called black matters. The 

 white deposit, consists of water 108 ; soluble salts 48*8 ; 

 insoluble matter 39-8 = 99-4. The insoluble portion con- 

 tains, sub-alum 71*8; proto-chloride of copper 5"0; chloride 

 of silver 8*5 ; oxide of iron 14* ; metallic gold - 776 = 

 100 - 076. The black matters consist of, water 13" 1 ; soluble 

 salts 44*5; insoluble matter 41 # 8. The insoluble matter 

 contained oxide of iron 64" ; oxide of copper 26* ; metallic 

 gold 5*08; metallic silver 1*12 = 96*2. The assayers fuse 

 the black matters with a mixture of potash, pearlash and 

 borax to extract the gold and silver. The composition of 

 the deposit from the colour waters, shews that in the action 

 which the mixture of salts exercises upon the alloy plunged 

 in the boiling sauce, the alum is decomposed, and aban- 

 dons sulphate of potash and a great part of its sulphuric 

 acid, to be transformed into a double insoluble sub-salt. 

 The sulphuric acid which the potash loses, is taken up by 

 the potash of the nitre, and by the sodium of the sea-salt, 

 converted into soda by the agency of the nitric acid set at 

 liberty. 



By the process described then, the concentrated colour- 

 water dissolves a portion of the gold at the temperature of 

 ebullition ; the metal remains in the liquid in the state of 

 chloride, and a deposit of sub-alum takes place. The silver 

 is still more strongly attached and is converted into chloride, 

 and if the proportion of marine salt is sufficient, this chlo- 

 ride dissolves like the gold, but on cooling, a portion 

 separates, and if the liquor is much diluted with water, the 

 remainder precipitates and the solution only retains slight 

 traces.* 



Pyruric acid. — This acid was obtained by distilling tar- 



* Ann. de Cliim. lx. 



