THE YOUNG SCIENTIST. 
7 
this completely. In our next, we shall 
tell of other methods of heating water in 
vessels which are not usually supposed to 
be capable of resisting fire. 
Crystals Under the Microscope. 
AMONGST the favorite objects of the 
early microscopists were crystals of 
different salts. Baker, in his book, " Em- 
ployment for the Microscope," describes 
almost all the salts at that time known, 
and he even attempts to identify various 
plants by means of the different appear- 
ances of the crystals formed by the salts 
obtained by leaching their ashes. And 
even now, when the young microscopist 
has not succeeded in procuring a good 
" And " of microscopic plants or animals, 
a few of the more easily procured salts 
will furnish a great deal of pleasant and 
instructive amusement. 
Crystals may be easily mounted for 
preservation and further examination, 
but it will be found that altogether the 
most interesting sight is the actual forma- 
tion of the crystals under the eye of the 
observer. For this purpose a little nitre, 
sal ammoniac, or any other salt that crys- 
talizes in needle-shaped or feathery crys- 
tals, gives the most beautiful results. A 
little of the salt having been dissolved in 
water, a drop is placed upon a well- 
cleaned slide (which has been slightly 
warmed) and spread evenly in a thin 
layer. No cover glass is used as we wish 
the liquid to evaporate quickly. The slide 
having been placed upon the stage of the 
microscope in a few seconds crystals are 
seen to form and shoot out over the en- 
tire surface of the field of view. The 
scene of minute forest growth cannot be 
described ; it is too surprising and beauti- 
ful. Fortunately, however, the experi- 
ment is so easily tried that any one that 
has a microscope can see it for himself. 
One word of caution may be necessary. 
In very cold weather the microscope 
should be warmed, so that the moisture 
from the slide may not condense on the 
lenses of the microscope and dim them. 
Some salts crystallize in very curious 
forms. Thus salicine takes the form of 
beautiful circles, with rays proceeding 
from the centre. The same is the case 
with the compound formed of iodine and 
sulphate of quinine, and when crystals of 
salicine or quinidine are viewed by polar- 
Fig. 1. CRYSTALS OF QUINIDINE SEEN BY POLARIZED 
LIGHT. 
ized light, the sight is a most beautiful 
one. The entire field is seen to be filled 
with circles, each containing a little cross, 
which, as the polarizer turns, revolves 
like a little wind mill. When, in connec- 
tion with the polarizer, a selenite plate 
Fig. 2. SPIRAL CRYSTALS OF SULPHATE OF COPPER, 
is used, the sight is one of the most beau- 
tiful that can be imagined. The little 
crosses shown in Fig. 1, instead of being 
black and w^hite, are gorgeously colored 
with red and green, blue and yellow. 
When pure solutions of salts are mixed 
