Miscellaneous Intelligence. 451 
tree et | iB Iv. | v. | vi. | via. fvini.| 3x. ; . | XII { xa, 
Tra ra~ |T ra- |Perti-/Reti-'Reti-Per- | Ob- | Eu- |P. Mela-} Ba-|Black} Por- 
chyte chyte| nite. ‘nite, nite, |lite alle rite.|gonite phyre salt | leva. phyry 
Siltca ie ived by potash, 36-0 00 i % ee 12:23) 9 £0)19°5: | | 11-45! 7-05 | 850 | 7 6C; : in 335. 
Alum 1-16} 1-25) 18 378) 1-55} 2:10} 220° 2 8h i. 
Total = of rock va | } 9 
— er — ition lars 5| 27°27 30 89 16 at i BE] 24 hes eed 20/18°60 | 18-41 [15 3&| 8°50 | 5°80 
the residue. } : 
L Brownish red Trachyte with gray globules and blackish mica, from Hungary. 
IL Trachyte “ molaire,” with a little orthoclase and mica, from Hungary. 
IIL. Blackish brown Pertinite, from Planitz. 
a Globulous Retinite of a —— color, from Meissen. 
. Retinite without lustre, ery r esinous, from Sardinia. 
VEG Grayish white and black Perit, shies Cape de Gata 
VIL Deep black Obsidian, from Lipar 
VILL Argillaceous Eurite, of a tir re di coker; from Saxony. 
IX. Mist iane brow igre lagonite, with a resinoid paste, from Teeland. 
X. Mel aphyre with a dark walt paste containing greenish-white Labradorite, 
from Belfah 
. ea _ a backs paste and Bie ewe of Bt from Bohemia. 
XITL Bla n Lava, from the s of 
XML Qunrtaierous oak yry with a  oaltilat sisas of a reddish-gray color and 
glassy quartz, from Saxony, 
pals 
The cS general conclusions may be ded 
When a rock is attacked by an alkali, some ning as well as silica 
is removed, with also some water, potash and soda ; besides also a litile 
ime, magnesia, and traces.of oxyd of iron. The amount of silica re- 
moved exceeds that of all the other substances. 
The alumina and water follow next after the silica in amount removed. 
Granite is not thus attacked when boiled with an alkaline solution ; 
Quariziferous Porphyry is feebly attacked, losing sone 2 hundredths. 
Lava, Basalt, and Melaphyre, lose less than 20 per 
Trachyte, Retinite, Perlite and Obsidian, suffer tos Taree loss, but 
rock containing water is attacked much less readily by alkalies af- 
ter it has been calcined ; for the Perlite of Cape de Gata, for example, 
the loss before and after ee is nearly as 23 to 
A rock is much more easily attacked when partially decomposed. 
Argillaceous Eurites or Kaolins, which are only desomateed granitic 
rocks, experience a much greater loss than the granitic roc 
Other things sil, the action of the alkalies is greater the larger 
the amount of silica, or the oe crystalline their structure, and the less 
of hyaline quartz they conta 
The vitreous rocks, wich: eoitaie little or no quartz, like Retinite, 
Faplite. Obsidian, Trachyte, are strongly attacked by alkalies. 
substit ituting alkaline carbonates for the alkalies, phir rocks, and 
BSA 5 the vitreous, are still attacked, but to a less extent. 
The facility with which the alkalies and even the alkaline carbonates 
attack rocks, shows that it is difficult to use them for separating the free 
or immediately soluble silica which may exist in a rock, especia 
in clays and kaolins 
I observe, also, that in obsidian, for example, the silica which is dis- 
solved is not free silica, but it is in the condition of a silicate attackable 
by the alkali; so also with Retinite, the silica is not in the state of opal, 
as — satiate but in that of an attackable hydrosilicate. Ina 
