On the non-existence of polarizing Silica, ete. 357 
dence is removed by decantation. If the mass resists the action 
of the alkaline liquor a still stronger solution should be tried, as 
while some specimens break up instantly in a weak solution of 
alkali, others require that it should be of the consistence of a 
dense syrup. The mud also should be poured off as fast as it 
tm so as to remain as short a time as possible in the caustic 
e 
The only specimens which I have found not to give good re- 
sults by the method above given, are those from Tampa Bay, 
Florida, and the infusorial marls from Barbadoes. In the masses 
tom Tampa the lapidification is so complete, that the alkali de- 
Stroys the shells before the lumps break np; and in the case of the 
Barbadoes marls the cementing material is calcareous, and requires 
a dilute acid for its removal. In applying the above process one 
catition is necessary, which is to thoroughly wash the shells with 
water, and not with acids, as the latter will cause the deposit of 
@ portion of the dissolved silica and materially injure the beauty 
of the specimens. When the washings are no longer alkaline, 
the specimens may then be thoroughly cleansed by acids or by 
the chlorate process described in the last number of this Journal. 
(See vol. xxi, p. 145.) 
— 
Arr. XXXVI.—On the non-existence of polarizing Silica in the 
Organic Kingdoms; by Prof. J. W. Batwey. 
It is now more than twenty years since Sir David Brewster 
announced the existence of polarizing or doubly refractive silica in 
the cuticle of Eguisetum, and in that of some of the grasses. In 
Lindley’s Natural System of Botany, the following account of 
Brewster’s experiments is given. ‘On subjecting a portion of the 
cuticle of Equisetum hyemale to the analysis of polarized light 
under a high magnifying power, Brewster detected a beautiful 
arrangement of the siliceous particles, which are distributed in 
two lines parallel to the axis of the stem and extending over the 
Whole surface. * * * Brewster also observed the remarkable fact 
at each particle has a regular axis of double refraction. Tn the 
straw and chaff of wheat, barley, oats and rye he noticed analo- 
gous phenomena.” (Quoted by Lindley from Grevill. F'l. Edi- 
hens., 214, 
In Quekett’s Treatise on the Microscope, 3d ed., p. 358, d 
rections are given for preparing the siliceous cuticle of Equisetum 
yemale for microscopic examination, by boiling in strong nitric 
acid, and it is added that ‘‘in balsam it forms a beautiful object 
for polarized light.” Similar directions are given for preparing 
the silica in the chaff of wheat, oats, &c. 
