26 THE NORTHERN MICROSCOPIST. 

which it was obtained, his hearers or readers will be able to pro- 
duce, without many failures, a similar slide ; but though failures 
when frequent are very discouraging they are ofttimes not utter loss, 
for those slides which do not shew the desired form of Micro- 
crystallization may, if examined carefully, exhibit other forms 
equally or possibly more interesting or beautiful. 
Plant culture, which affords ample scope for enthusiasts, also 
illustrates well what I mean; for where one man aims to produce F 
superior plants of a well-known species, another will devote him- : 
self to the production, by cross fertilization or different methods of 
cultivation, of other and newer forms and varieties. Upon the same 
principle, workers in the subject before us to-night aim—some to 
a prepare superior slides of typical crystals, others by making solu- 
tions of different strengths and in various media, by working at 
higher or lower temperature, and by adding foreign substances— 
| to obtain, like the plant grower, new varieties and beautiful forms 
which shall not only delight the sight, but exertise the mind of the 
observer. 
! In describing the mode of preparation of some of the Micro- 
crystals, those which are most readily prepared have been selected, 
—one of the easiest being Tartaric Acid; this, like many others of 
j the “ common objects of the Microscope,” is very beautiful, and is 
| thus prepared. 
| Make a strong solution in water of the Acid Crystals, and having 
t warmed a slide, drop on the centre a little of the solution and 
evaporate by gentle heat, that is by holding the slide some four or 
five inches above the flame of the spirit lamp. If only a small 
drop of the solution has been used, the crystals will be thin, and 
will require a selenite to bring out their utmost beauty ; but if the 
drop of solution is heaped up, as it were, on the slide, the crystalliza- 
tion will be stronger and will not need the selenite, but as the 
| polarizer is rotated, the colour will be well shewn. 
i Immediately following this, may be mentioned Gallic Acid, of 
i which a moderately strong solution is to be made in methylated 
‘spirit. Drop a little of this solution in centre of cold slide and allow 
i to evaporate very slowly ; if, however, smaller crystals are desired, as 
i soon as the slightest appearance of crystallization is visible, slightly, 
i very slightly warm the slide. A third and different form of crystal 
is obtained by adding together saturated solutions of the acid, both 
in water and methylated spirit ; then placing a little of the mixture 
on centre of warm slide, and as soon as the crystals commence to 
form, pricking the centre with a cold needle. 
i The preparation of the slides from these two acids separately, 
i naturally at this point leads me to notice a form of crystal obtain- 
able by a mixture of the two as follows: 
Make a strong solution of each in methylated spirits, and then 

a a 


