77 0 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
[March 29, 1873. 
such accidents—angular magnitude is always rigidly pre¬ 
served. 
My second example of the action of crystallizing force 
■ is thus : By sending a voltaic current through a liquid 
you know that we decompose the liquid, and if it contains 
a metal we liberate this metal by the electrolysis. This 
•small cell contains a solution of sugar of lead, and this 
substance is chosen because lead lends itself so freely to 
This, crys tallizing power. Into the cell dip two very thin 
iplatinum wires, and these are connected by other wires 
with a small voltaic battery. On sending the voltaic cur¬ 
rent through the solution, the lead will be slowly severed 
from the atoms with which it is now combined; it will be 
liberated upon one of the wires, and at the moment of its 
lliberation it will obey the polar forces of its atoms, and 
produce crystalline forms of exquisite beauty. They are 
now before you, sprouting like ferns from the wire, appear¬ 
ing indeed like vegetable growth rendered so rapid as 
*to be plainly visible to the naked eye. On reversing the 
current, these wonderful lead-fronds will dissolve, while 
from the other wire filaments of lead dart through the 
-liquid. In a moment or two the growth of the lead-trees 
■recommences, but they now cover the other wire. In 
'the process of crystallization, Nature first reveals herself 
.as a builder. Where do her operations stop ? Does she 
continue by the play of the same forces to form the 
^vegetable, and afterward the animal ? Whatever the 
■answer to these questions may be, trust me that the 
motions of the coming generations regarding this myste- 
.rious thing, which some have called “brute matter,” will 
* be very different from those of the generations past. 
There is hardly a more beautiful and instructive example 
• of this play of molecular force than that furnished by the 
case of water. You have seen the exquisite frond-like 
t forms produced by the crystallization of a film of water on 
a cold window-pane. You have also probably noticed the 
•■beautiful rosettes tied together by the crystallizing force 
■during the descent of a snow-shower on a very calm day. 
The slopes and summits of the Alps are loaded in winter 
with these blossoms of the frost. They vary infinitely in 
■detail of beauty, but the same angular magnitude is pre¬ 
served throughout. An inflexible power binds spears and 
spiculae to the angle of 60°. The common ice of our lakes 
is also ruled in its deposition by the same angle. You 
may sometimes see in freezing water small crystals of 
stellar shapes, each star consisting of six rays, with this 
.angle of 60° between every two of them. This structure 
miay be revealed in ordinary ice. In a sunbeam, or failing 
That, in our electric beam, we have an instrument delicate 
<.enough to unlock the frozen molecules without disturbing 
Rhe order of their architecture. 
According to the emission theory, the velocity of light 
fin water and glass is greater than in air; according to the 
undulating theory, the reverse is the case. This point has 
fbeen subjected to the test of an experiment proposed by 
Arago, and executed by Foucault and Fizeau, and decided 
in favour of the undulatory theory. Whenever the two 
theories have come into collision this has been the result. 
Consider a small portion of a wave issuing from a point 
of light so distant that the portion may be regarded as 
practically straight. Moving vertically downwards, and 
impinging on a horizontal surface of glass, the wave would 
go through the glass without change of direction. But, 
-as the velocity in glass is less than the velocity in air, the 
wave would be retarded in passing into the denser medium. 
But suppose the wave, before reaching the glass, to be 
oblique to the surface ; that end of the wave which first 
^reaches the glass will be the first retarded, the other por¬ 
tions as they enter the glass being retarded in succession. 
This retardation of the one end of the wave causes it to 
swing round and change its front, so that when the wave 
Fas fully entered the glass its course is oblique to its 
original direction. According to the undulatory theory, 
light is thus refracted. 
The two elements of rapidity of propagation, both of 
-Sound and light, in any substance whatever, are elasticity 
and density, and the enormous velocity of light is attain¬ 
able because the ether is at the same time of infinitesimal 
density and of enormous elasticity. It surrounds the 
atoms of all bodies, but seems to be so acted upon by them 
that its density is increased without a proportionate in¬ 
crease of elasticity ; this would account for the diminished 
velocity of light in refracting bodies. Now, in virtue of 
the crystalline architecture that we have been considering, 
the ether in many crystals possesses different densities in 
different directions ; and the consequence is that some of 
these media transmit light with two different velocities. 
Now, refraction depends wholly upon the change of velocity 
being greatest where the density is greatest. Hence in 
many crystals we have two different refractions, a ray of 
light being divided by such crystals into two. This effect 
is called double refraction. 
In water, for example, there is nothing in the grouping 
of the molecules to interfere with the perfect homogeneity 
of the ether; but, when water crystallizes to ice, the 
case is different. In a plate of ice the elasticity of the 
ether in a direction perpendicular to the surface of 
freezing is different from what it is parallel to the sur¬ 
face of freezing; ice is, therefore, a double refracting 
substance. Double refraction is displayed in a particu¬ 
larly impressive manner by Iceland spar, which is crystal¬ 
lized carbonate of lime ; the difference of ethereal density 
in two directions in this crystal is very great, the separa¬ 
tion of the two halves of the beam being, therefore, 
particularly striking. Upon the screen is now projected 
an image of our carbon points. Introducing the spar, 
I permit the beam which builds the image to pass through 
it; instantly you have the single image divided into two 
others. Casting upon the screen an image of the aperture 
through which the light issues from the electric lamp, 
and introducing the spar, two luminous disks instead of 
one appear immediately upon the screen. 
The two beams into which the spar divides the single 
incident-beam do not behave alike. One of them obeys 
the ordinary law of refraction discovered by Snell, and 
this is called the ordinary ray. The other does not obey 
the ordinary law. Its index of refraction, for example, 
is not constant, nor do the incident and refracted rays 
always lie in the same plane. It is, therefore, called the 
extraordinary ray. Pour water and bisulphide of carbon 
into two cups of the same depth ; looked at through the 
liquid, the cup that contains the more strongly-refracting 
liquid will appear shallower than the other. Place a 
piece of Iceland spar over a dot of ink ; the two dots are 
seen, but one appears nearer than the other. The nearest 
dot belongs to the most strongly-refracted ray, in this case 
the ordinary ray. Turn the spar round; the extraordinary 
image of the spot rotates round the ordinary one. 
The double refraction of Iceland spar was first treated 
of in a work published by Erasmus Bartholimus, in 1669. 
The celebrated Huyghens sought to account for the 
phenomenon on the principle of the wave theory, and he 
succeeded in doing so. He made highly important obser¬ 
vations on the distinctive characters of the two beams 
transmitted by the spar. Newton, reflecting on the 
observations of Huyghens, came to the conclusion that 
each of the beams had two sides ; and from the analogy 
of this two-sidedness with the two-endedness of a magnet, 
wherein consists its polarity, the two beams came to be 
described as polarized. 
(To be continued.) 
SYRUP OF LACTO-PHOSPHATE OF LIME. 
Take of Chloride of Calcium . , . 
Phosphate of Soda . . . ?iv 
Concentrated Lactic Acid . gi. 
Dissolve the chloride of calcium and phosphate of soda 
separately, and mix the solutions; wash the precipitate 
and dissolve in the acid. Filter and mix with sufficient 
syrup to make two and one-half pints. — E. Chiles, in 
American Journal of Pharmacy. 
