1825.] 
matter of much importance, especially to 
country residents. These accidents fre- 
quently arise from knots, where the glass is 
Jess perfectly annealed, and from inequality 
ef thickness at the lower end, preventing 
uniform expansion by the heat. The best 
method of detecting the knots is to examine 
thé glasses by depolarized light, rejecting 
those that exhibit depolarized tints. M. 
Cadet de Vaux (Bull. des Sc. Teg.) pro- 
‘poses to remedy the evils resulting from un- 
equal thickness, by cutting round the lower 
part of the tube with a diamond; which 
precaution being taken, he adds, in an es- 
tablishment where six lamps are in constant 
use, nine years have passed without a single 
glass being broken. 
Potato Paint.—Take a pound of poia- 
toes, skinned and well baked; bruise them 
4n three or four times that weight of boiling 
water, and then pass them through a hair- 
sieye. Add two pounds of fine chalk in 
powder, - previously _ mixed with double 
the weight of water, and stir the whole well 
together. This mixture will form a glue, to 
which any colouring powder may be added, 
eyen charcoal, brick, or seot, for painting 
‘gate-posts, &c. exposed to the action of the 
air-—Brewster’s Jour. 
Professor Leslie —This able practical 
philosopher is, at present, as we are given 
to understand by a brief notice in Jameson’s 
Ed. Ph. Jour., engaged in an important 
series of experiments ‘‘ on the deposition 
of humidity from damp air. 
_ Formation of Ores by the Action of the 
Atmosphere and Volcanic Heat.—The for- 
mation of Brown Hematite, by the action of 
water on cast-iron pipes, having been no- 
ticed, Néggerath, in the third volume of 
his work, “Des Gebirge in Rheinland, 
Westphalen, ” mentions the fragment of a 
_ Roman copper vessel, dug up at Bonn, in 
the territory of Cologne, Germany, and co- 
wered, inside and out, with a delicate layer 
of small byt beautiful dodecahedral, and 
' cube-octahedral red'copper crystals, imme- 
Aliately over which was a thin film of a 
green colour, which might be called mala- 
_ chite. Wrought pieces of copper, appa- 
rently architectural ornaments, have also 
been observed at Treves, in the circle of 
Lower Rhine, so corroded on the surface 
as, almost; to have lost their original form. 
‘Some traces of gilding were, however, vi- 
‘sible ;“and, under the green crust, or erugo, 
was" ‘a Tayer of well marked red copper 
c The Bonn yessel appears to have 
Fathi 2d to the action of considerable 
heat } but at Treves, and in the specimens 
‘enumerated below, no vestige of fire was 
diseérniblé. “ Sage observed red copper 
stals on an old copper statue, found in . 
the ce . _&e. mixed in certain phoportione, “with 
the Soane, in Tuseany, in the year 1766. 
_ Demeste mentions red copper, crystals, seen 
‘in the. hollow» fragments of the leg of a 
bronze-horse, ‘which hadi been, buried. for 
some hundred vyears:),Morveauw describes 
Spirit of Philosophical Discovery. 
339 
these crystals as of two kinds—one, ruby- 
red,—the other, emerald-green ; and De- 
meste also states that there were crystals 
of blue malachite or copper in some of the 
hollows. Vauquelin informs us. that, .on 
examining the fragment of a long-buried 
statue, the exterior was found to be red- 
copper, the interior in a metallic state: 
these changes must have been produced. by 
the action of the atmosphere and perco- 
lating water, or by fusion. Similar exam- 
ples were found in masses of copper,. in- 
closed in the lava which, in 1794, flowed 
over great part of the country round Torre 
del Greco. The surface of copper coins, 
converted into red-copper, was crystallized, 
while the interior was radiated. In some 
specimens of brass candlesticks, from Torre 
del Greco, preserved in the Museum of the 
University ef Edinburgh, the zinc has se- 
parated from the copper; on some are 
small brownish crystals of translucent blende, 
numerous octahedrons of red-copper, and 
very beautiful copper-red cubes of pure 
metal. In other specimens, from Vesu- 
vius, the zine and copper have separated, 
and each appears, conformably, crystallized. 
Masses of iron, partly crystallized in .octa- 
hedrons, and partly in the state of iron 
glance and sparry iron, have been found in 
the lava of Vesuvius. Silver, in beautiful 
octahedrons ; lead, in the state of litharge ; 
and galena, or lead-glance, in the cubo- 
octahedral form, haye been, also, collected 
from the lava of Torre del Greco.— 
Schweigger’s Journal. 
Sitometer.—Mr. Steffen has sraybetted, 
and describes in the last Number of Jame- 
son’s Edin. Phil. Journal (p. 269, &c.),’an 
instrument, with a warning-bell attached, 
which seems admirably adapted to super- 
sede the Wick-Stick and Tally, among far- 
mers and corn-merchants. It is spoken of 
as being particularly useful and desirable : 
but probably the prejudices that so gene- 
rally prevail against tnnovation, as it is 
called, will induce an adherence to ancient 
and clumsy contrivances, and retard, if not 
prevent, the extensive use of “the Sito- 
meter.” 
Cooling of Glass.—Bellani finds that 
glass, having been exposed to great heat, 
never regains its original volume. 
Evaporation.—M. Pouillet, from experi- 
ments he has made, infers,—1. That, during 
the evaporation of perfectly pure water, no 
electricity isevolved. 2. That, when water 
contains certain alkalies in solution, elec- 
tricity is evolved, which is vitreous for the 
apparatus when the alkali is fixed, and’ te- 
sinous when the alkali is volatile, as amuno- 
nia.—Jam, Ed. Ph. Jour. 
Artificial Cold.— 7Ether, spirit of wine, d 
snow, afford temperatures as joys as thibee 
produced by sea-salt. / a ee 
Indian Yellow, — The Jaune ‘Indien, 
sik 
-brought from Manilla, isa ¢ a 
2x2 irons 
