102 Preparations of Gold lately employed medicinally > 



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

 any judgement from the figure of the salt. 



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

 muriatic solution of gold, saturated carbonate of potash 

 will precipitate the copper, without throwing down the gold, 

 if no heat be employed. 



As too larsre 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, to boil the solution at every additicm of a'kali, and 

 to separate the precipitate by filtration, whenever a sensible 

 quantity appears. 



The precipitate must be washed but slij^htiy, it being 

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

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

 wise it will be a iTiixture of oxide and metallic gold. 



It may be known whether the oxide be pure, bv treating 

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

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

 will remain undissolved. 



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

 tien also recommends, may be obtained either wiih 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. When this ceases to be re- produced, 

 the liquor is to be filtered, and the precipitate washed in 

 distilled water, dried in the shade, and powdered. This is 

 the purple powder of Cassius. 



If the oxide of gold be precipitated bv a solution of tin, 

 It is of imp' rtance that the tin be in a fixed stale of oxida- 

 tion, otherwise the product will vary both in its nature and 

 quantity. A uniform solution may always be obtained bv 

 dissolving slips of tin in muriatic acid at 12° [I"089]» fil- 

 tering, evaporating to the point of crystallization, dissolving 

 the crystals in pure water, and filtering again. Part of this 

 solution should immediately be mixed with the liquid mu- 

 riate of gold ; and the I'uion of the two salts produces a 

 precipitate, which should be increased by adding fresh quan- 

 tities of the muriate of tin, as long as any thing is thrown 

 down ; after which the precipitate is to be washed, dried, 

 and powdered. 1 he quantity obtained, appears to depend 

 on the quantity of water added to the solutions of gold and 

 tin. The more they are diluted, the more the tin is thrown 



down. 



