250 ON PREPARATIONS OF GOLD. 



soda, nearly like that of Stahl's alkaline martial tincture. 

 !No change in the limpidity of these mixtures takes place on 

 standing. : ,• 



Barytes and lime do not produce the same colour in the 

 solution of gold, no doubt on account of the great quantity" 

 of water employed in their solution. 

 «n!e*5 as-isfed ^^> after the acid of the solution of gold has been corn- 

 by hear, pletely satui-ated by potash,- the mixture be heated, a red 

 substance separates in a very bulky flocculent form, much 

 resembling in appearance oxide of iron at a maximum. 

 P/eeiuitate If an excess of caustic alkali, even though very trifling, 

 with excess of be put into the mixture, and it be boiled, the bulk of the 

 precipitate will diminish greatly, and it will appear of a 

 brown colovir, when seen in a body; though it is in reality 

 lilue, for the particles of matter suspended in the liquor, 

 vihich of itself is sUghth/ yeUoiCi make it appear green*. 

 The m on- '^ '''^ liquid, from wiiich I had precipitated the matter 

 >:r'uirn ^ti'.lre- abovemenlioned by means of potash, was colourless; but, 

 ffold^ *°"'^ '^^ soon as it 'was 5;aturated with muriatic acid, it suddenly 

 assumed a yellow hue, li1te that of the common solution of 

 gold, and sulphate of iron threw down metallic gold from 

 It. 

 Thr precipi- ^^^ *^^6 washings of the precipitate, to the last, gave wgns 

 latesiightiy of the presence of gold ; which seems to indicate, that this 

 niatter is slightly soluble in water. The last washings how- 

 ever contained less than the first. 

 A i" n f I- When the liquors contain a certain quantity of gold, the 

 phateofiron precipitate formed in them by sulphate ''of iron presently 

 d^FercHr T(v" "^'^""^^*^ ^ brown colour; but when they contain only a 

 jjortioiis. little of this metal, no precipitate is formed immediately, 

 the liquid only becoming of a fine transparent indigo blue. 

 At length however, a black powder is deposited, leaving the 

 liquid colourless. 



_, , r , . This observation seems to prove, that when gold is in a 

 Colourof gold. . . . ' ' ? , . 



state of minute division, it appears blue; and that it as- 



* Two thihgs are hare taken for granted ; that the precipitate is ho- 

 moge!ieo\is„aiid that the suspended particles are precisely the sadie ■with 

 it. Frora the next paraj^raph too it would appear, that the "slightly 

 yeliow'* liquid is calourlobS. C. 



suraes 



