TRANSACTIONS OF THE SECTIONS. 
59 
Crvsials generally arise from the deposition of fresh matter upon an original cry- 
Miae nucleus, so that the formation of the interior part of the crystal is prior m 
nit of time to the exterior parts. But in the case ot fused nitre, the formation of 
ierhole crystal is simultaneous, and is doubtlessly produced by the contraction ot 
tr liquid mam in one rftrec<i«n, producing an energetic internal tension. 
Store eitcmal pressure (produced by screws, &e.) causes glass to assume a weak, 
Wih refracdug structure, air D. Brewster bus conjectured that all double refraction 
iwinr to a permanent internal tension of the particles of Iransporcnt bodtea, caused 
fitm by their molecular attractions. 
This experiment on nitre seems to prove the theory to be true. ludeea tliat a con- 
•dnble tension takes place in the nitre when it grows cold and solidifies, la nianifest 
hs tbs particle sometime* cracking in two. When it docs so, the two portions on 
ifereot aides of the crack become each of them a perfect crystal, but ibe two crystals 
We not the least relation to each other iu respect of the position of their axes, which 
dBiice alone determineii. Hence it is evident the crack lakes place owing to differ- 
I at portions of the crystal, while cooling, tendlug to ccoiiract in diffewnt directions; 
vi B it is probable that there must be a tendency in a thouasnd dilferent particles 
kcoBtract masm&ny diii'creatdireciionSf it is remarkable that, unless u crack actu^y 
hhs plsce, ^ese irregnlar tendencies arc overpowered, and the contracllou 
iWe in one determinate direction (perhaps the resultant of all the others). The 
'Bth of this is manifest from tlie employment of polarired light a»^ a means of raa- 
Wiiiion, for that would immediately detect the least IrrcBularity in the crystalhue 
*MWre. If the different portions of the fused particle did not all possess the same 
'WetioD of crystalline axis, part of it would dcpolarUo the incident polanzcd ught, 
»V51e another part did not do so. But such is not the case, for all the portions niam- 
the same action with eutire accuracy. Hence the conclusiwi seems irresiatible, 
•hit ill the case of nitre, a strongly dcvclo]>ed internal crystalline structure w diie to 
■"thing eke than internal tension, which tension took place ainultaiieoitf ly throughout 
•k whole tnasii when it grew cold, oiid without in the least affecting either ita size or 
k at«iial outline. ... 
But.since the growtji of crystals of nitre, like that of other salts, from a small pn- 
aitive crystalline nucleus ia a fact capable of easy obeewalicii, and that one fact can* 
•it poadbly be destroyed or in any way altered by another fact, it follows that the 
ihovenew principle of crystallization is not to be viewed as in any way hostile to the 
“nittouly received theory, but merely as aupplementnry to it, and as uflbrding (it is 
•fcrived) an «xpcrifnwilal proof In favour of the truth of Sir D. Brewster’s theory 
*h'>»e-meationed. . 
The experiment above described was first published by tlie author in the Pliuoso* 
|f>icsl Magazine, vohxii. p. H5, but as he did not on that occasion draw the atten- 
h®" of the scientific world to the important thooretical couscijucnces which appear to 
k drducible from it, he thought it was not unworthy of being brought before the 
••trntion of tbs Chemical Section on the present occasion. 
On Biliary Concretions. By Dr. De Vrii. 
Thii was an examination by Dr. De Vrii, made with a view of ascertaining, par- 
•f'llsrly, if the presence of copper could be detected in these concretions. It would 
*PP®ar. from the Doctor's researches, that iU presence is purely accidental, and by 
w means constant. _ 
Oti the Analyses of ike Inorganic CoiisHiuents of Organic Bodies. 
By Dr. De Vrii. 
Br.DcVrii wished to call especial attention to the necessity of obsemng minu^Iy 
IJ* precaution recently insisted upon by I’rof. H. Bose in ® 
of the inorganic constituenta of org.inic matter—as of the blood, fo P * 
ilt. De Vrii haviug made comparative experiments for deterrammg t ^ Q ^ 
«pl<u»ic matter in Wood by the usual mode of incineration, and ?>’ 
consists in treating the residue, after careful carbonization, with dilute hydro* 
^loric acid, obtained one-fourth more inorganic matter by the latter than by th 
