102 
Cryftals of Alum. 
The regular Cryftals are often formed in 
the fame Drop with the other Configura¬ 
tions, as at f. But if not, they may eafily 
be produced, either by ufing a Solution 
made with hot Water, before it cools ; or 
by placing a Drop of a well-faturated Solu¬ 
tion, when cold, on a Slip of Glafs, and 
differing the Fluid to evaporate without 
any Heat at all. Cryftals will alfo be form¬ 
ed by Precipitation after the Solution has 
flood fome Time. 
After numberlefs Gbfervations to deter¬ 
mine the Cryftals of Alum ,, I find amongft 
them the following Variey : 
Some are exactly regular Odlaedra, com- 
pofed of eight equilateral Triangles, as the 
Figure A. 
But as they lie mod frequently on one of 
their triangular Bafes, they appear in the 
Manner fhewn at B. 
Others appear like the above with their 
folid Angles cut off, forming thereby a 
Figure of fourteen Sides, eight of which 
are Hexagons, and the other fix Squares, 
as C. 
The Figure D frequently prefents itfelf, 
and feems alfo compoied of fourteen Planes 
(viz. 12 quadrilateral, and two hexagonal) 
the Planes underneath being fuppofed to 
correfpond in Number and Figure with 
thofe that appear above*. 
E repre- 
