Chemical Science. 183 



21. On the Detection of small quantities of Mercury. — Mr. Smithson, 

 some time since, described a very sensible test of the presence of 

 mercury in solution, consisting in the immersion of a gold ring or 

 plate into the solution, a piece of tin foil having been previously 

 rolled round it, and a few drops of muriatic acid being added to 

 the liquid. This small voltaic pile caused a deposition of any 

 mercury present upon the gold, which became white in con- 

 sequence. If, on applying heat to the ring or plate, the gold re- 

 sumed its yellow appearance, the proof was considered perfect. 

 M. Orfila, in applying this test, found some preparations gave all 

 these appearances, and yet contained no mercury ; and led by this 

 to make various trials, he found that the tin foil might be dissolved 

 by the acid, and then precipitated on the gold, giving the white 

 appearance, wiiich disappeared on the action of heat. He found 

 that the gold and tin, if put separately into a mercurial solution, 

 would not indicate the mercury by a white appearance on the gold. 

 He found also that gold, whitened by the deposition of tin and of 

 mercury, might be distinguished by pure strong muriatic acid, 

 which dissolved the tin but not the mercury, and therefore restored 

 the yellow colour of the gold in the former, but not in the latter 

 case ; but he thinks, that, though with this precaution and addi- 

 tional trial, the presence of mercury may be almost certainly ascer- 

 tained in solution, yet still that the proof is not complete except 

 the gold plate is put into a little glass tube, and the mercury driven 

 off by heat, and being condensed above, is recognized as mercury 

 in the metallic state. With these precautions, he admits that the 

 use of Mr. Smithson's small voltaic pile affords the most delicate 

 test known for small portions of mercury in solution. — Ann. de 

 Chimie, xli. 92. 



22. On the Coloration of Golden Articles of Jewellery, by M. 

 Castellani. — The two best mixtures, according to M. Castellani, for 

 the purpose of giving a good gold colour to articles of jewellery, are 

 as follows : — 



Muriatic acid at 22° ... 10 parts 



Oil of vitriol .... 4 



Crystallized boracic acid . . 2 



Water 150 



Or, ..... 



Acid muriate of alumina (liquid) . . 13 parts 



Crystallized sulphate of soda . ... 4 

 Crystallized boracic acid . . , . 3 



Water 150 



Either of these mixtures, with twenty grains of neutral muriate of 

 gold, constitutes the bath, which is Jo be us^ed in the following 

 manner : — A large glass matrass, carefully luted at the bottom, is 

 placed over a circular furnace, so as to have heat readily applied to 

 it ; the solution is to be put into it, and when at the boiling point, 

 the pieces of jewellery, previously cleaned and picked, are to be 



