
TRANSACTIONS OF THE SECTIONS. 4l 
a longer time, but with nearly all the substances enumerated it is distinct, and with 
some of them quite intense. 
2. By an independent series of experiments to determine the effects of heat, which 
were made upon the taches of potassa and soda and their carbonates, and upon those 
of carbonate of lime and magnesia, as well as upon considerable quantities of these 
substances successively exposed in a crucible to the heat of the table blowpipe, it 
was found that the order of volatility was as follows :—potassa, soda, magnesia, lime. 
The tache of potassa disappeared almost at once, that of soda lingered some time, 
that of magnesia wasted more slowly, while that of lime remained with little altera- 
tion for a long time. 
Before heat was applied the tache of the alkalies or their carbonates would of course 
‘be strongly alkaline. That of the carbonate of magnesia also presented a decided 

and sometimes strong reaction with the test-paper, while that of carbonate of lime 
gave a merely appreciable effect. But on raising the tache to a red heat, the car- 
bonate of lime, by escape of carbonic acid, would acquire intense alkalinity, the re- 
action of the magnesia ¢ache would be but little altered, and that of the alkaline 
taches would be almiost or entirely. destroyed. 
As examples of this distinctive testing and of the mode of proceeding in these ¢ache 
experiments, Professors Rogers gave some details, extracted from the large mass of 
unpublished results, and called attention particularly to the contrasting phenomena 
in the cases of Leucite, Olivine and Epidote; the first characterized by potassa, the 
second by magnesia, and the last by lime. 
Thus in the case of Leucite, the water tache and carbonic acid water tache were 
both alkaline, the latter very strongly so. But even gentle ignition for a few seconds, 
or strong ignition for a moment, was found entirely to dissipate the alkali. 
In the case of Olivine, the water tache was decidedly alkaline, and that from car- 
bonic acid water greatly more so. Ignition produced for the first second or two but 
little change, but its continuance caused a gradual diminuticn of the alkaline re- 
action, which at the end of ten seconds was reduced to about one-twelfth of what it 
was at first. 
With Epidote the tacke presented an extremely feeble reaction before heating. 
Ignited for a moment, the alkalinity was intense, and after ten seconds of ignition but 
little abatement of the alkaline reaction was discerned. 
3. Referring to the second method of experimenting used by the Professors Rogers, 
viz. that of prolonged digestion in water or carbonic acid water, Profs. Rogers exhibited 
results obtained with hornblende, epidote, chlorite, mesotype, &c., showing that the 
amount of solid matter dissolved by the carbonated water in many of these cases is 
quite sufficient for a qualitative analysis, even when the digestion has only been con- 
tinued for forty-eight hours. When further prolonged, they have procured from the 
liquid a quantity of lime, magnesia, oxide of iron, alumina, silica and alkali, the dis- 
solved ingredients of these minerals severally amounting sometimes to nearly one 
per cent. of the whole mass. ‘ 
4, In connection with the preceding investigations, the Professors Rogers were led to 
an examination of the comparative solubility of carbonate of lime and carbonate of mag- 
nesia in carbonated water. In the standard chemical and geological works the car- 
bonate of lime is stated to be the more soluble, and on this supposed fact is founded 
a common theory of the origin of the large quantities of carbonate of magnesia in 
the magnesian limestones. It was conceived that in a mixed limestone containing 
both the carbonates, the relative amount of carbonate of magnesia would be augmented 
through the more rapid removal of the carbonate of lime by the percolating waters, 
a that thus the mass would approach more and more to the composition of a do- 
omite, 
The experiments of the Professors Rogers demonstrate that in water impregnated 
with carbonic acid, carbonate of magnesia is much more soluble than carbonate of lime. 
Thus, by allowing the slightly-carbonated water to filter through a mass of magnesian 
limestone in fine powder, and collecting the clear liquid, analysis detected a much 
larger proportion of carbonate of magnesia in the soluticn, in comparison with the 
carbonate of lime, than corresponded with the amount of these substances relatively 
in the powdered rock. Again, by agitating briskly a quantity of the powder with the 
carbonated water in a glass vessel and then separating the liquid by filtration, it was 
