Preparations of Gold lately employed medicinally. 101 



turated solution of gold by murialic acid, a yellow precipi- 

 tate is formed*, which, when collected on a filter, does 

 not amount to more than 40 grs. of oxide from 72 grs. of 

 the metal in the solutipn. The remaining liquid is of a 

 very deep colour, and contains a triple muriate of gold and 

 potash. A fresh quantity of the caustic alkali will cause 

 no further precipitation, unless the liquid be kept several 

 hours in a gentle heat : but in this case, a new precipitate 

 will fall down, extremely bulky, and of a deeper colour 

 than the former, and apparently at a different degree of 

 oxidation. Several weeks are necessary to complete th« 

 precipitation; and even at last a certain portioii of gold 

 will remain, which must be thrown down by a slip of tin, 

 if we would lose nothing. 



If the solution of gold be very acid, there will be scarcely 

 any perceptible precipitation ; and this might be expected, 

 as 'the alkali finds a sufficient quantity of free acid, to form 

 muriate of potash enough for the production of the triple 

 salt. Indeed, no precipitation at all ought to take place, 

 when the solution is extremely acid ; but here, experience 

 does not entirely agree with theory, for a very siTiall quan- 

 tity, of oxide of gold is always produced. 



The causticity of the potash is of great importance; for 

 if the neutral carbonate be employed", no change will take 

 place without the assistance of heat. This, expelling a 

 considerable portion of carbonic acid gas, will alter the 

 colour of the solution from yellow to greenish. If it be 

 then filtered, traces of the purple oxide of gold will be 

 found; and it will effervesce with acids, having its fine 

 golden colour restored. A few drops added to a glass of 

 water will not cdluur it; but, if the water be acidulated, 

 the colour will instantly appear. The same solution yields 

 by evaporation white, transparent, alkaline crystals, inter- 

 spersed with black spots. The^e crystals dissolve \n water 

 without colouring it ; and on filtering the solution it passes 

 tranjpavent, leaving a littk gold on the filter. The ad- 

 dition of any acid, however, causes its colour to re-ap- 

 ptar. 



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 carbonic 

 and muriatic acid, potash, and golii ; but whether consti- 

 tuting a quadruple salt, a triple, or two salts, one the 

 triple muriate of gold and p,)tash, the other subcarbonate 



• It U a«cei»arv to emplov heat. 



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