1 58 Intelligence and Miscellaneous Articles. 



of protonitrate of mercury, and a deep violet precipitate of protoxide 

 of gold is formed ; sometimes the precipitate does not separate, and 

 the oxide remains apparently dissolved ; but by heat, the precipitate 

 separates immediately ; in this operation it is essential not to use an 

 excess of the mercurial salt, for it would produce protochloride, on 

 account of the presence of the hydrochloric acid which accompanies 

 the reaction ; it is sufficient not to precipitate the whole of the gold, 

 and to stop while the solution remains slightly coloured yellow with 

 the undecomposed chloride of gold. 



2nd. The decomposition of protochloride of gold by potash is a 

 good method of preparing protoxide of gold, but there are precautions 

 which are indispensable to be observed in order to obtain a pure pro- 

 duct : evaporate a solution of chloride of gold to dryness, and heat 

 the residue on a sand-bath, the temperature of which is determined 

 by a thermometer ; the mass is to be continually agitated till it as- 

 sumes a very bright canary-yellow colour, taking care that the tem- 

 perature does not exceed 302° Fahr. ; at a higher temperature the 

 protochloride loses the greater part of its chlorine. 



If potash be then poured on the mixture, a dark violet precipitate 

 of protoxide of gold separates, and the solution has a deep yellow 

 colour, owing to the potash having dissolved a part of the protoxide 

 of gold ; after filtration nitric acid is to be added, so as very accu- 

 rately to saturate the potash, and precipitate the oxide of gold which 

 it held in solution, in the state of a gelatinous hydrate of a deep 

 violet colour ; excess of nitric acid must be avoided, for the aqua 

 regia which it would form, would dissolve the product ; it is better 

 to let the solution remain slightly alkaline ; the products of these 

 operations are to be collected on the same filter. 



3rd. If concentrated acetic acid be boiled with tritoxide of gold 

 obtained by decomposing aurate of potash with nitric acid, the fil- 

 tered liquor has a deep yellow colour, and by evaporating it nearly 

 to dryness, the separation of a very considerable quantity of protoxide 

 of gold takes place. 



4th. The tritoxide of gold (auric acid) recently prepared from the 

 aurate of magnesia or barytes, being diffused through a solution of 

 potash or soda, readily dissolves and forms a solution of a golden 

 yellow colour ; if this solution be submitted to evaporation, protoxide 

 of gold is always precipitated, whatsoever means of evaporation be 

 employed, either without the contact of air or spontaneous evapora- 

 tion. 



This precipitation is especially active at a boiling heat ; the solu- 

 tion becomes quickly turbid and deposits a greenish precipitate, pro- 

 bably the tritoxide, and this is soon followed by an abundant deposit 

 of violet protoxide of gold ; this reaction continues in a singular 

 manner, and solutions which contained only about 300 grains of 

 gold, will continue to become turbid and to deposit protoxide of gold, 

 after having boiled for nearly two days. 



5th. The neutral chloride of gold, treated with potash or soda, 

 forme, after long- continued ebullition, so considerable a quantity of 



