Blow-pipe.—Galvanic Troughs. 145 
vegetation will continve some time healthy in an atmospheré of 
carbonic acid gas. That the vegetable functions act differently 
from those’of “animals, is evident from the fact, that until the 
oxides of iron are /igalthful to the animal ceconomy, they are 
destructive to the process of vegetation. If the carbonic acid 
gas was at ail equivalent to the oxygen set free, whence comes 
the carbon which builds up the curious structure of the plant? 
The partial quantity of carbonic acid which plants respire, 1s 
evolved during night; and this being condensed by the cool cf 
the evening, and mingling with the dews of this season of repose, 
will not deteriorate the atmosphere, but be absorbed by the soil 
on which it falls, and minister anew to the requirements of the 
plant. Besides, in winter, the plant being denuded of its foli- 
age has its inspiratory and expiratory organs comparatively 
suspended ; while the period when these powers are uncontrolled 
and most active is marked by a much longer sojourn of the sun 
above the verge of the horizon. And J may add in conelusion, 
the sentiment of Brisseau Mirbel: “* in Europe, while our vege- 
tables, stripped by the severity of the season of their foliage, no 
longer yield the air contributing to life, the salutary gas is borne 
to us by trade-winds from the southernmost regions of America. 
Winds from all quarters of the globe intermingle thus the various 
strata of the atmosphere, and kvep its constitution uuiform in 
all seasons and in all elevations.” 
Being in the habit of frequently experimenting with the blow- 
pipe of condensed oxygen and hydrogea, Dr. Clarke’s late com- 
munication in Dr. Thomson’s Annals of Philosophy afforded me 
particular interest. Besides oi] from its trauquil ebullition af- 
fording no index of safety, the disadvantage pointed out is as 
unexpected as important. During my course of chemical lec- 
tures at Greenock, | used water in the safety cistern, and my 
experiments were splendid and imposing. In the use of this 
instrument at Paisley, in my late lecture, the illustrations were 
feeble in effect and unimposing, and I have often since wondered 
at the circumstance ;—now at this time [ used oz instead of wa- 
ter, and Dr. Clarke has fortunately solved the question. It ap- 
pears then that o// will never do. “a 
I may conclude these miscellanea by adverting to a very cu- 
rious circumstance which occurred to me here during my lecture 
on galvanism. 1 used three porcelain troughs with triads upon 
the principle of Dr. Wollaston. The fluid medium employed 
was diluted nitric and muriatie acids. I had omitted inad- 
vertently the beautiful experiment of the ignition of platinum 
wire, until the action of the troughs was so feeble that it would 
not affect a hair’s breadth of the metal. I immediately pro- 
posed, by way of experiment, to withdraw the plates from the 
Vol. 50, No.232, August 1817. K cells, 
