in the Compounds of Zinc and Antimony. 231 
ef such experiments were given in the former memoir in a table, 
a mere glance at which will discover the two following facts— 
Ist, That up to 40 per cent no great increase in the amount of 
hydrogen evolved is obtained by increasing the amount of zine in 
the alloy. 
2nd, That at the alloy containing 42 per cent. of zinc there is 
an immense maximum confined at most between two per cent on 
either side. 
General Conclusions. —Before stating the conclusions to which 
as I think the facts now established directly point, it will be well 
to consider the only two admitted principles of chemical science 
which could possibly be brought forward to explain similar varia- 
tions. They are, first, that of impurities in crystals; second, that 
of isomorphous mixtures. It will not be difficult to show that 
the variations in composition of Sb Znz and Sb Zns cannot be 
caused by either of these principles. 
It is a well known fact that crystals trequently talke up impuri- 
ties which are either dissolved or mechanically suspended in the 
menstruum in which they form, and it might be supposed at first 
sight that the excess of zinc or antimony in Sb Zns or Sb Zne, 
ore the same relation to their crystals that the sand does to the 
thombohedron of calcite from Fontainebleau, or oxyd of iron 
and chlorite to crystals of quartz; but, in the first place, in all 
cases where a considerable amount of impurity is present the 
crystals are either imperfect or else the angle is considerably 
changed at times even as much as two or three degrees; and 
secondly, as such impurities are merely mechanical, the amount in 
the crystals would in all probability be proportional to the amount 
present in the menstruum at the time of their formation. Now in 
shows that it is, by the chemical force. 
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