VI. METALS.~SuB-sALT8. 243 



COBALT. 



Cobalt black, Oxide of cobalt. Boil powdered bright-white 

 cobalt ore. found in Cornwall, in nitric acid ; dilute with a large 

 quantity of water ; add subcarbonate of potash water, in small 

 successive portions, letting the solution settle, and decanting off 

 the clear each time until it becomes of a rose colour : then add 

 subcarbonate of potash water as long as any sediment falls, which 

 wash and dry : used to make blue colours for painters and 

 potters. 



2. Dissolve cobalt in muriatic acid, and add subcarb. of potash 

 water; filter and wash : used in rheumatism. 



METALLIC SUB-SALTS. 



GOLD. 



AuEUM FULMiNANs, Oxiclum auri ammoniatum. Dissolve a 

 few grains of grain-gold in aqua regia made with common salt, or 

 by the mixture of the acids, and add liquid ammonia, to preci- 

 pitate the gold. 



^. Dis>solve gold in aqua regia made with sal ammoniac, and 

 precipitate the gold with subcarb. of potash water ; requires much 

 care, as it explodes with the utmost violence on the least friction, 

 or a very slight heat : its fulminating quahty may be destroyed, 

 and the gold recovered, by boiling it in oil of vitriol or oil of tar- 

 tar, as also by mixing it with sulphur, and exposing it to a gentle 

 fire, which burns the sulphur away ; it first becomes purple, and 

 then appears in its metallic form. Aurum fulminans is sedative, 

 antispasmodic, and carminative ; used in spasmodic colic, in doses 

 ofgr. iij— vj. 



SILVER. 



Fulminating silver, Bruf/Jifddirs fulminatijig powder. Dis- 

 ■olve silver gr. xl, in nitric acid 3ij, or lunar caustic 3j, in dis- 

 tilled water ."^ij ; to this solution add spirit of wine ."^ij, and boil 

 the mixture in a retort, or flask, so that the condensed steam may 

 run back into the boihng liquid ; a white crystalline powder forms 

 at the bottom ; when no more seems to form, let it cool ; wash 

 • the fulminating silver with river water, and dry it between bibu- 

 lous paper, but without heat. Explodes with the slightest friction : 

 a small portion, alxnit l-.jd of a grain, being put in the middle of 

 • bit of silver pajTer, the edge of which is smeared with ])aste, a 

 bubble of gla.s3 is then wrapj)c'd up in this paper ; the bubble thus 

 loaded will explode, if thrown upon the ground or trml upon ; is 

 a ^ood alarm, if put in places where it may be trodden upon by 

 thieies, &c. 



