174 BULLETIN OF THE BUSSEY INSTITUTION. 
at 100° C.) and in this ash he found 41.40% of silica, besides an abun- 
dance of potash, lime, phosphoric acid, &c. In Hquisetum Telmateja, 
dried at 100° C., he found 28.57% of ash, and in the ash 66.15% of 
silica. These numbers correspond to 7.82% of silica in the plant 
itself of H. arvense, and to 18.90% in #. Telmateja, both dried at 
100°. 
A student in Wicke’s laboratory, Brock,* is said to have found 
83.16% of silica in the ash of H. hyemale. 
Some determinations of silica by Struve,t which have been cited here 
and there as illustrating the large amount of silica (95 to 97.50% !) in 
equisetum ash, have really no such meaning; since the analyses were 
made neither upon equisetum plants nor upon their natural ashes, but 
upon certain products that had been prepared from the ashes by 
leaching them with water and acids. 
On contrasting the amounts of ashes and of silica that have been 
found in the equisetums with the amounts contained in the straw of 
some of the cereal grains, it will be seen that it is the large amount of 
ash in the equisetum plants, rather than the proportion of silica in that 
ash, which makes the quantity of silica in the plant itself so much larger 
than it is in the straws. More than 70% of silica has often been found 
in the ash of the straw of winter wheat, for example; and from 60 to 
65% of silica is not infrequently found in the ashes of rye-straw. But 
in dry wheat-straw containing 5% of ash, of which 70% was silica, 
there would be only 3.50% of silica in the straw; and in rye-straw con- 
taining 5% of ash, of which 65% was silica, there would be 3.25% of 
silica in the straw: whereas, when Braconnot found 45.99%, and 
Witting 41% of silica in the ash of Hgucsetum arvense, they found, re- 
spectively, 13.84% and 18.89% of ashes in the dry plants, and these 
numbers are equivalent to 6.38% and 7.82% of silica in the plants, 
or twice as much as in the straws above cited. In the great water 
horse-tail of Europe, #. fluviatile, there has been found as much as 
12 lbs. of silica in 100 lbs. of the dry plant; and in another great 
European horse-tail (Z. Telmateja), 18.9 lbs. of silica to 100 lbs. of the 
plant. 
For the sake of controlling the estimations of silicic acid in Z. ar- 
vense that have been given above on page 168, I procured a fair sample 
* “ Annalen der Chemie und Pharmacie,” 1856, 97. 849. 
t Poggendorff’s “‘ Annalen,” 1849, 76. 359: 
