Chap. 34.] Mode of dying the Hair brown. 219 



derable quantity of lead, and then expofed on the cupel 

 in a ftate of fufion. The lead is vitrified and abibrbed 

 into the cupel, carrying with it the imperfect metals, 

 and the filver remains behind on the cupel in a pure 

 ftate. 



The vitriolic acid acts on filver as on the other me- 

 tals, with the afiiftance of heat ; it then corrodes it into 

 a white mafs, which is foluble in water, and by evapo- 

 ration affords fmall cryftals. 



The nitrous acid diflblves filver with great rapidity. 

 When the (Irong nitrous acid is diluted with an equal 

 weight of water, it is capable of difiblving about half 

 its weight of filver. If the filver employed is quite 

 pure, the folution is limpid like water; but as filver 

 commonly contains a little copper, its folutions have 

 ufually a blueifli tinge. If the filver employed con- 

 tains gold, in this cafe, as the nitrous acid is not capa- 

 ble of diffolving the gold, it feparates from the filver 

 in the form of blackifh flocks. From this difference 

 in the action of nitrous acid on filver and gold, it is 

 fuccefsfully ufed to feparate thefe metals from each 

 other. 



The folution of filver in the nitrous acid is extremely 

 bitter and cauftic, and has the property of changing 

 the Ikin or hair to a black colour, or, if very much, 

 diluted, to a brown, and formerly, when the caprice 

 of fafhion abhorred light hair as much as it at prefent 

 admires it, was employed for that purpofe. The co- 

 lour is, however, very faint when the folution is firft 

 applied, and the production of colour feems in a great 

 meafure to depend on the action of light. Dr. Lewis 

 mentions a remarkable phenomenon, which this folu- 

 tion prefents when added to chalk or any pure abfor- 

 bent earth. The chalk and folution are both at firft 

 quite white, and will continue fo if kept in a dark 



place, 



