Chemical Science. 393 



anomalies, and serves to show how difficult it is to judge of the true 

 intensity of chemical action exerted upon a substance by liquids in 

 contact with it *. 



19. CRYSTALLIZATION OF BISMUTH. 



M. Quesneville, fiU, says, that by the following process, magnificent 

 crystals of this metal may be obtained. Bismuth is to be fused in a 

 crucible, fragments of nitre added from time to time, and the heat raised 

 so as to decompose the nitre, and the whole mixed by agitation. Con- 

 tinuing the heat and the addition of nitre in this way for some hours, 

 a time arrives when a little of the metal agitated in the air exhibits 

 magnificent green and golden-yellow colours, which it retains when 

 cold. If the metal displays only rose, violet, or indigo colours, and 

 when cold is a white mass without colour, it is certain that good 

 crystallization will not occur. When the metal is in right condition, 

 it is to be poured into a ladle previously heated ; and to prevent the 

 surface cooling faster than the bottom, it should be covered, or a hot 

 shovel held near it. The cooling should not be too slow, for then 

 the metal crystallizes layer by layer, and offers no fine forms ; it is 

 necessary that the cooling be rather sudden. When the upper crust 

 has formed, it should be pierced by a hot coal, and not by percus- 

 sion (which disturbs the crystals), and the remaining liquid metal 

 decanted. In about half an hour longer the rest of the crust may 

 be broken, and the interior will be found magnificently crystallized, 

 the crystals being more beautiful as the above conditions have been 

 more carefully followed f. 



20. ON DISCOLOURED CHLORIDE OF SILVER. (M. Cavalier.') 



Chloride of silver blackened by sun-light is perfectly well known. 

 M. Cavalier obtains it in a similar state by dissolving the recent 

 chloride in ammonia, and passing chlorine gas into the solution; 

 the usual decomposition of ammonia with elevation of temperature, 

 evolution of azote, &c., takes place, and ultimately the liquid becomes 

 turbid, and the chloride of silver appears first as a grey, and then, 

 when the ammonia is entirely decomposed, as a violet precipitate. 



This precipitate dissolves entirely in ammonia, and is precipitated 

 in a perfectly white state by pure nitric acid. If 20 grains of it be 

 decomposed by zinc in dilute sulphuric acid, it yields 15 grains of 

 silver, exactly the quantity yielded by similar treatment from 20 grains 

 of white chloride. Hence the difference of the chloride in these two 

 states cannot be referred to difference of composition, but solely to 

 some variation in molecular arrangement J. 



* Bib. Univ. 1830, p. 391. t Jour, de Pharmacie, 1830, p. 534. 



J Jour, de Pharmacie, 1830, p. 553. 



