212 DAVIES, ON CRYSTALLIZATION AND THE MICROSCOPE. 
acid neutralized by the addition of carbonate of soda. This 
solution must then be spread evenly upon the glass slide 
and the whole warmed, but not raised to any great degree of 
heat. There will then remain upon the slide an amorphous 
film, with which nothing must come into contact. In a dry 
place, protected from all chance of dust, it must then he laid ; 
and in a time, varying from two or three days to as many 
weeks, the crystals will have risen up in particularly hand- 
some shapes. In circular specimens the cross is always very 
decided, an example of which I send in Photograph No. 4. 
Where there has been interference a wave is sometimes called 
forth, very closely resembling No. 2, crystal of santonie, in 
‘Microscopical Journal, October, 1864, but the waves are 
more regularly formed, and rendered still more beautiful by 
the well-defined cross. In another slide, where some im- 
purity had caused the formation of crystals to commence 
unusually early, the waves went from that poimt with such 
uninterrupted long sweeps that it is certamly no exaggera- 
tion to call it a sea of colour when on the stage, even with- 
out any selenite plate to assist. Some few slides I have 
covered with the solution, and never could call forth any 
crystal of decided form upon them, either by long keeping or 
the application of heat. 
Enough for the present concerning different classes of 
crystallization. From these it is plain that, though the 
system to which the forms belong is seldom changed, the 
crystals are so varied as microscopic objects that an intimate 
knowledge of the substances is required to recognise them. 
As an example of this may be quoted snow—this belongs to 
System III, the rhombohedic, yet the forms are so varied 
that, perhaps, nothing shows a greater number of exqui- 
sitely beautiful designs. In a paper read by T. G. Rylands, 
Esq., before the Scientific Section of the Historic Society of 
Lancashire and Cheshire, April 26th, 1855, and printed for 
private distribution, forty different forms of crystal are given, 
some of which are of most intricate design, and of such 
variety that none except those who had studied the subject 
could believe that they were the same substance. 
It appears to me that the science of crystallization is yet 
in a very imperfect state, and requires much investigation. 
Let every one, therefore, who studies the subject give his ex- 
perience, so that all knowledge of it may be brought to- 
gether, and thus we shall arrive at results otherwise unat- 
tainable. 
