V 



CHEMISTKY. 225 



prisms, with a square base 8 or 10 centimetres in the side, and 12 or 16 centi- 

 metres high. The edges are rounded, and a hole is made in one end of a con- 

 venient size. Sometimes an inner crucible is used, each having its own cover. 

 When the substance to be heated is very refractory, only one crucible is used? 

 and the walls of this are made 3 or 4 centimetres thick. The base of the cru- 

 cible must be 5 or 6 centimetres below the bottom of the cavity. The space 

 between the crucible and the walls of the cylinder must be 5 or 6 centimetres. 

 In using a lime crucible, charcoal is first to be introduced, little by little, till 

 the crucible is covered ; the heat is then very gradually increased till the cru- 

 cible becomes red, when the coals are removed to make sure that the crucible 

 is not cracked, after which the heat may be urged to the utmost. The second 

 kind of crucible is of carbon. The author uses gas-retort carbon, and fashions 

 it on a lathe. To free the material from impurities, it may then be strongly 

 heated in a current of chlorine, by which process it loses weight. These cruci- 

 bles are placed within crucibles of lime, the intervening space being filled with 

 calcined alumina. The third species of crucible is made of alumina, obtained 

 by calcining ammonia-alum. Thus prepared, it is plastic, but shrinks much on 

 drying. To prevent this, the author mixes the mass with a calcined mix- 

 ture of alumina and marble. A mixture of plastic and alumina, calcined 

 alumina, and aluminate of lime, in equal parts, gives a very hard and 

 infusible mass, which softens a little at the melting point of platinum. Once 

 backed, these crucibles resist all tests ; even sodium has no action on them. 

 The lime crucibles may be used whenever the alkali is not injurious ; the car- 

 bon crucibles have a more limited use hi consequence of their reducing 

 agencj r . The alumina crucibles may be used almost always when lime will not 

 answer. With respect to the heat produced by this furnace, the author gives 

 the following details : Platinum fuses in a crucible of lime into a single well 

 united button. This platinum possesses properties very diflerent from those of 

 ordinary platinum condensed from the sponge. When copper is plated with 

 the fused platinum rolled out into a very thin sheet, nitric acid has no action 

 whatever, as it does not penetrate the leaf of metal. A plate made from fused 

 platinum does not cause the union of oxygen and hydrogen even after several 

 hours. Fused platinum possesses a perfect softness and malleability. In a cru- 

 cible of carbon, platinum melts easily but yields a brittle alloy of platinum, car- 

 bon, and silicon. By raising the heat above the temperature required for fusion, 

 Deville succeeded in volatilizing the metal with remarkable ease, so that it con- 

 densed hi small globules. Pure peroxyd of manganese heated with carbon from 

 sugar hi quantity less than sufficient to reduce the oxyd, gave fused metallic 

 manganese as a brittle mass, having a rose reflection like bismuth, and as 

 easily reduced to powder. Its power decomposed water at a little above the 

 ordinary temperature. Chromium as prepared in a similar manner was weD 

 fused, but not into a button, at the temperature at which platinum volatilizes. 

 The metal is brittle and cuts glass like a diamond. It is easily attacked by 

 chlorhydric acid, but little by sulphuric acid, and not at ah 1 by nitric acid, either" 

 strong or weak. Metallic nickel fuses to a homogeneous button which may 

 be forged with great facility. It has a ductility almost without limit, and is 

 more tenacious than iron in the ratio of 90 to 60, according to Wortheim's ex- 



