316 Intelligence and Miscellaneous Articles. 



chloride of gold at a boiling heat with bicarbonate of potash, till 

 effervescence ceases : 2nd, by precipitation with magnesia, as recom- 

 mended by Pelletier. The first of these processes, as it is generally 

 effected in the laboratory, yields but a very small quantity of the 

 oxide, for an excess of the alkaline salt readily redissolves the oxide 

 of gold precipitated, forming a double chloride of gold and potassium 

 and aurate of potash. The magnesia process succeeds much better, 

 though it is tedious, and a considerable quantity of the metal is con- 

 verted into chloride of gold and magnesium. 



M. Figuier prefers the following process :— precipitate the solution 

 of gold by carbonate of soda, and convert afterwards the small quan- 

 tity of gold which remains in the liquors, into aurate of soda, which 

 is to be afterwards decomposed by sulphuric acid, so as to set the 

 auric acid free : the following is M. Figuier's description of the pro- 

 cess : — 



Evaporate the common solution of gold nearly to dryness, redis- 

 solving with a few drops of aqua regia the light deposit of proto- 

 chloride of gold, which always remains by the action of the heat. 

 Dissolve the chloride in water, and saturate the brown solution which 

 remains very accurately with carbonate of soda, either dissolved or 

 solid, and as free as possible from chloride, to prevent the formation 

 of the double chloride of sodium and gold. The liquor is to be made 

 to boil, preserving its neutrality very exactly. It is to be boiled for 

 half an hour, or rather till heat ceases to occasion precipitation. 



By this process the greater part of the gold is precipitated of a 

 fawn colour. In operating on about 460 grains of gold, only about 

 63 remained in the liquor separated from the precipitate ; and this 

 may be converted into auric acid by a process stated by M. Figuier, 



The teroxide of gold prepared by means of magnesia, contains 

 after drying in vacuo or by exposure to the air, 29 per cent, or 10 

 equivalents of water ; and this is also the case when it is prepared 

 by precipitating the aurate of potash with nitric acid ; but the ter- 

 oxide obtained by means of carbonate of soda contains only 24 per 

 cent, or 8 equivalents of water. If it be attempted to deprive these 

 oxides of the water which they contain by means of the water-bath, 

 they do not lose it without a portion being reduced by the heat ; so 

 that when auric acid is required quite free from reduced gold, it must 

 be dried either in vacuo or by exposure to the air ; this oxide is reduced 

 at 473° F. ; at common temperatures hydrogen has no effect upon 

 it, but when the temperature is slightly raised, it reduces it very 

 quickly ; when a current of this gas, dried by chloride of calcium is 

 directed upon auric acid contained in a small glass tube, and a part 

 of the oxide is very gently heated, it bums directly and vividly, and 

 a beautiful flame, which is at first green and then red, pervades the 

 train of oxide. The gold remains in the metallic state. 



Iodine, when moderately heated, in the presence of water with 

 auric acid, yields a milky liquid, which soon deposits a bright yellow 

 powder. If the mixture be boiled, the iodide is reduced and deposits 

 the gold ; M. Figuier has not analysed this compound, but supposes 

 it to be periodide of gold, which has not hitherto been isolated. Al- 

 cohol when cold has no action on auric acid, obtained by the satu- 



