182 



MEDICINAL PREPARATIONS OF GOLD. 



Crvsr.a's pro- 

 duced. 



Their nature. 



Carbonate of 

 potash sepa- 

 rates copper 

 from sold. 



Too much al- 

 kali not to be 

 employed. 



The oxide to 

 be washed but 

 lightiy. 



Test of its 

 purity. 



Oxide preci- 

 pitated by tin. 



Precipitate 

 -with ir.esallic 

 fin. 



the colour will instantly appear. The same solution yields 

 by evaporation white, transparent, alkaline crystals, inter- 

 spersed with black spots. These crystals dissolve in water 

 without colouring it; and on filtering the solution it passes 

 through transparent, leaving a little gold on the filter. 

 The addition of any acid however causes its colour to re- 

 appear. 



What is the chemical nature of the crystals obtained? 

 Though this was not minutely ascertained for want of 

 time, it appears certain, that they were composed of car- 

 bonic and muriatic acid, potash, and gold : but whether ■ 

 constituting a quadruple salt, a trisule, or two salts, one the 

 triple muriate of gold and potash, the other subcarbonate 

 of potash, the authors cannot say ; nor could they form 

 any judgment from the figure of the salt. 



It may not be amiss to observe, that, in an impure 

 nitvemuriatic solution of gold, saturated carbonate of pot- 

 ash will precipitate the copper, without throwing down the 

 gold, if no heat be employed. 



As too large a quantity of alkali, added to a solution 

 of muriate of gold, will cause a portion of the precipitated 

 oxide to be redissolved ; it is necessary, to add the alkali 

 cautiously, boil the solution at every addition of alkali, 

 and separate the precipitate by filtration, whenever a sensi- 

 ble quantity appears. 



The precipitate must be washed but slightly, it being 

 partly soluble in water, as Mr. Vauquelin remarked ; and 

 it must be dried in the shade and in a cool place, otherwise 

 it will be a mixture of oxide and metallic gold. 



It may' be known whether the oxide be pure, by treating 

 it with muriatic acid, which in this case will dissolve it 

 completely; but, if it be mixed with metallic gold, part 

 will remain undissolved. 



The oxide of gold precipitated by tin, which Dr. Chres- 

 taeU also recommends, may be obtained either with metallic 

 tin, or with its solution. 



For the first, slips of tin well cleaned are to be put into an 

 aqueous solution of muriate of gold. These will soon be 

 covered with a layer of pulverulent matter, of a colour more 

 or less deep; which will be renewed several times, after being 



removed 



