216 On the Formation of Microscopie [Mn cS tbo. 
taneously to many persons by means of the oxy-hydrogen microscope, 
either with or without the addition of polariscope effects. 
Further, I believe that the facts which I am about briefly to 
describe deserve attention as having an important bearing on the 
subject of the modification of crystalline polarity by mechanical 
force. 
The method in question consists in enclosing a very small 
quantity of a saturated or nearly saturated solution of any given 
substance at a high temperature in thin cells, and hermetically 
sealing them before crystallization takes place. It is necessary to 
describe in some detail the manipulation required to ensure success. 
First, then, an ordinary ring of gold-size must be “spun” upon 
a glass slip, using the size largely diluted with turpentine, by which 
means a cell is obtained of extreme thinness and perfectly smooth 
surface. This should then be baked in an oven for some hours, in 
order to bring it into such a condition that subsequent exposure 
to a high temperature shall not perceptibly soften it. 
Immediately before use, the cell should be placed on the turn- 
table and the least possible quantity of fresh gold-size applied to it 
with a brush, the edge of the glass cover being similarly treated. 
The object of this precaution is to ensure immediate contact between 
the two without allowing the solution to wet either. The glass slip 
and cover must be placed in readiness on a hot plate and brought 
up to a temperature closely approaching the boiling-point of water, 
and the brass dise of the turn-table heated to a like degree. 
The strength of the solution to be used is best ascertained by a 
few preliminary trials. 
A drop of the hot solution is then placed in the cell, the cover 
adjusted as quickly as possible, the superfluous liquid pressed out 
and removed with blotting-paper, and the whole transferred instantly 
to the hot turn-table and hermetically closed by a pretty copious 
application of gold-size, which does not enter the cell, if the pre- 
cautions above described have been adopted. 
On transferring the slide to the stage of the microscope a most 
exquisite spectacle is witnessed. 
Crystallization rapidly ensues, the crystals extending over the 
field in forms necessarily of extreme tenuity and corresponding 
translucency, their transparency being enhanced by the fact of their 
being bathed in their own mother-liquors ; and as a consequence, 
EXPLANATION OF PLATE LXII. 
The upper figure represents freshly-formed crystals of chlorate of potash, depo- 
sited ina very thin closed cell from a solution saturated at a temperature immediately 
below its boiling-point—magnified 8 diameters. 
The two sides of the lower figure represent the successive phases of re-solution 
of portions of the same crystals after the lapse of half an hour and twelve hours 
respectively—magnified 25 diameters. 
