Of Salts in Mineral Waters * 2 6^ 
common than any, namely, Calcarious Salt 9 
or Nitre . 
Green Vitriol is produced from the Iron 
Pyrites . When mature and perfect, its Cry- 
ftals are always pointed at each End, and 
confift of ten Planes with unequal Sides: that 
is, the four middle Planes are Pentagons, and 
each of the fharp Ends is made up of three 
triangular Planes, as Plate XIV. Fig . 4. 
Alum burnt, diffolved in Water, and drain¬ 
ed, affords Cryftals whofe Top and Bottom 
are two fexangular Planes, the Sides round, 
which appear compofed of three Planes that 
are likewife fexangular, and three double 
quadrangular ones, placed alternately. So 
that every perfect Cryftal confifts of eleven 
Planes, namely, five fexangular, and fix 
quadrangular. Fig. V. 
The Water of our Inland Salt-Springs af¬ 
fords Cryftals of an exacft cubical Form, one 
Side or Plane whereof feems to have a par¬ 
ticular Clearnefs in the Middle, as if fome 
Deficiency were in that Place ; but the other 
five Sides are white and folid. See Fig. VI. 
Sal Gem , diffolved, ihoots into the like 
cubic Cryftals. 
Sea-water boiled to Drynefs, and its Salt 
diffolved again in a little Spring-water, gives. 
Cryftals alfo that are cubical, but remarka¬ 
bly different from thofe laft defcribed : for 
in the Cryftals of Sea-fait all the Angles of 
the Cube are feemingly cut off, and the 
Corners 
