206 DAVIES, ON CRYSTALLIZATION AND THE MICROSCOPE. 
interferes with its neighbouring particles to such a degree 
that all visible evidence of the required formation is lost. 
This is, I think, proved by the fact of one perfect form being 
frequently found in the midst of a mass of uninfluenced salt. 
Still, in some cases the forms grow by well-defined grada- 
tions from the oblique prism to the perfect circular “flower.” 
Before, however, proceeding to these particular specimens 
which I purpose to discuss in this paper, I will mention an 
interesting example of crystallization which was thrust 
upon my notice in this town. A bread-baker, whose shop 
was very large, with plate glass windows, generally had 
the lower parts of these beautifully ‘ obscured” with some 
of the finest crystalline forms I had ever seen. On inquiry 
I found that the agent employed was ordinary sulphate of 
magnesia; but as this salt has generally small crystals, I 
begged for more exact information. Then I learned that the 
salt was dissolved in hot BEER, and the glass covered with 
the solution. But on the formation of the crystals there 
was little uniformity or beauty visible. The hot bread was 
then brought from the oven and laid upon shelves around 
the shop, which was very soon filled with a dense vapour. 
The crystals upon the windows were now redissolved, whilst 
the clearance of the vapour was so very gradual, and the 
amorphous syrup-like action of the deer at the same time 
aiding to prevent any sudden formation of crystal, that in- 
stead of being particularly minute many of the circles were 
three or four inches in diameter, and the whole was exqui- 
sitely beautiful. From my own experiments I am convinced 
that the size was appreciably increased by a restraining action 
(as I may term it) of the beer, so that where*any crystal was 
called to life there was less chance of any interfering forma- 
tion arising in its vicinity from sudden dryness or want of 
body, though the gradual removal of the bread’s vapour was 
the most active agent in the matter. 
After this digression we will resume our examination of 
cases where two salts are used together. As an agent in 
this class sulphate of magnesia, is very valuable. 
SutpHate oF Zinc anp Macnesia.—The sulphate of 
magnesia, commonly termed Hpsom salis, belongs to System 
V of Crystallization, being formed in oblique rhombic 
prisms. It contains seven atoms of water, but six of these 
are driven off by a comparatively low heat, the remaining 
atom requiring a great degree to remove it. When it is 
erystallized alone upon the slide it usually displays very little 
beauty of design, but I have found it resembling a mass of 
