406 | Prof. J. P. Cooke on the Variation of Constitution in a 
The crystals both of Sb Zn* and Sb Zn® can be obtained with 
great readiness. It is only necessary to melt together the two 
metals in the atomic proportions, and when the metals are fully 
alloyed, to proceed exactly as in crystallizing sulphur. The melted 
mass is allowed to cool until a crust forms on the surface, which 
is then broken, and the liquid metal remaining in the interior 
poured out. On subsequently breaking the crucible, the interior 
is found lined with magnificent metallic crystals, which, when not 
tarnished by oxidation, have a silver-white lustre. In the course 
of my investigations on these compounds, crystallizations were 
made, or attempted, of alloys differmg in composition by one 
half to five per cent., according to circumstances, from the 
alloy containing 95 per cent. of zine, to that contaiming 95 
per cent. of antimony; but only two crystalline forms were ob- 
served, that of Sb Zn* and that of Sb Zn®. The crystals of the 
two compounds both belong to the trimetric system; but they 
differ from each other, not only in their crystallographic elements, 
but also in their whole “habitus.” Stibiotrizincyle crystallizes 
in long acicular prisms, which group themselves together into 
larger prismatic aggregates; while stibiobizincyle crystallizes in 
broad plates, which twin together on an octahedral face, and 
form a very characteristic cellular structure. This very striking 
difference in the character of the crystals proved to be an im- 
portant circumstance in the investigation, as it enabled me to 
distinguish with certainty between the two compounds, even 
when the faces of the crystals were so imperfect that a measure- 
ment of angles was impossible. 
The most remarkable result of the mvestigation, and the one 
to which I wish to direct especial attention, is the fact that 
each of the two crystalline forms was found to be constant 
under very wide variations in the per-centage composition of the 
crystals. As this is a point of great importance, it will be 
necessary to enter more into detail, considering in the first 
place the crystals of Sb Zn®. The crystals of this compound are 
obtained in the greatest perfection from an alloy containing the 
two metals in just the proportions represented by the formula, 
namely, 42°8 parts of zine, and 57:2 parts of antimony. They 
are then comparatively large, generally aggregated, and, as the 
three analyses cited in the accompanying Table indicate, they 
have the same composition as the alloy. 
Composition of the alloy by Composition of the crystals by 
synthesis. analysis. 
Per cent. Per cent. Per cent. Per cent. Sum. 
of Zn. of Sb. of Zn of Sb. 
42°80 57°20 43°15 56°93 100-08 
43°06 56°50 99°56 . 
o Pa 42°83 57°24 100:07 © 
