On finking Fire with a Flint and Steel, g i y 
If album be burnt, diffolved in water, and {brained, its 
crydals will confift of two fexangular planes, whofe fides 
are bounded by fix other, three of which are quadrila¬ 
teral, having between them three of a fexangular figure.; 
as at fig. 548- 
Green vitriol affords crydals, which are made up of 
ten unequal Tided planes, the middle-moft are pentagons, 
and each of its {harp ends triangular planes; as at 
% 549 - 
The crydals of our inland falt-fiprings are of a cubical 
figure, as at fig. 550. 
Salt-petre {hoots into long crydals, whofe fides are fir 
parallelograms ; as at fig. 5 Ji¬ 
lt has been already mentioned, that vinegar owes its 
pungency to the falts which float therein ; their fhape k 
fecn at fig. 552. Expole a drop or two of vinegar to 
the open air for an hour or two upon the obje<ff-carrying 
giafs, that its watery parts may evaporate; then apply 
it to the microfcope. 
The falts of fugar candyed, are reprefented at fig. 55 y 
The fairs of nitre are feen at fig. 554. The falts of cam- 
phi re, at fig- 555. Sal gem is reprefented at fig. j.jfk 
and fill armoniack at fig. 557. 
It is bed: to examine all falts in the {mailed maffes 3 for 
in them their fhape will be bed dificovered. 
On finking fire with a Hint and flee!, &c« 
O N driking fire with a flint againd a deel, little 
particles of deel are druck of, and melted into 
globules by the collifion ; which will be evident .on 
Threading a fheet of white paper, and obferving the place 
v/here feveral of thefe little fparks feem to vanifh. Mr. 
Hook 
