340 ON TWO NEW CRYSTALLINE COMPOUNDS 



memoir, do not appear to have been included in any of these investigations. The pre- 

 vious knowledge in regard to them is given by Gmelin in his text-book in the follow- 

 ing words: "These two metals fuse together with facility, and, according to Gehlen 

 and A. Vogel, without emission of light, and form a hard, brittle, steel-colored alloy, 

 Avhose density is less than the medium density of its elements (Gellert)." * 



It will be the object of the present memoir to show, first, that zinc and antimony 

 fonn with each other two, and probably only two, definite compounds ; secondly, 

 that these compounds are capable of a very large variation in composition without any 

 change in the crystalline form ; and lastly, that this variation can only be explained by 

 admitting an actual perturbation in the law of definite proportions produced by the 

 influence of mass. The two compounds are 



I. Terantimonide of Zinc, or Stibiotrizinci/le, SbZn^. 



This may be best prepared by melting together 57 per cent of antimony and 43 per 

 cent of zinc,f and allowing the liquid mass when thoroughly mixed to cool until a 

 crust forms on the surface. On piercing through this crust, and turning out the still 

 liquid alloy, the crucible, if broken open when cold, will be found filled with the most 

 beautiful prismatic ciystals. These crystals are obtained in their greatest perfection 

 by employing eight or ten pounds of the alloy, and cooling the crucible very slowly in 

 sand. In order to insure a constant composition of the alloy, it is best to melt the 

 antimony first, and afterwards add the zinc in small portions, removing the crucible 

 from the fire as soon as the whole is melted, and stirring with a heated earthenware 

 rod. Moreover, in order to prevent oxidation of the crystals, it is important that the 

 hole pierced through the crust should be quite small, and it requires a little practice 

 to catch the exact moment when the crust is thick enough to support the mass of 

 melted metal in the crucible. 



The crystals thus obtained present the following properties. They have a very 

 brilliant metallic lustre and a silver-white color; (the surfaces are often, however, 

 iridescent, owing to a slight oxidation, and the true color is then only seen on the 

 fracture.) They are very brittle, and can readily be reduced to a grayish- white powder. 

 Their hardness = 3.5. The Sp. Gr. varies with the composition, as will be shown 

 hereafter ; that of crystals containing 43 per cent of zinc = 6.327 nearly. The form 

 is a rhombic prism belonging to the Trimetric System, with sometimes only one, but 



* Gmelin's Hand-Book, Cavendish ed., Vol. V. p. 50. 



t When the metals are not pure, it is best to make allowance for the impurity. 



