386 Natural-Philosophical Collections. 
products, or some of them, are sufficient to explain in general the formation of 
oxalic acid, but in some particular cases there ought to be other products ob- 
tained. Thus tartaric acid gives no sensible portion of hydrogen, and. yet its 
composition being 24 proportions of hydrogen, 4 of carbon, and 5 of oxygen, we 
cannot explain its transformation into oxalic acid by the occurrence of any of 
the known products. 
Tn fact, during the operation, the mixture remains perfectly white. -If all the 
carbon sural into the oxalic acid, it would require 6 proportions of oxygen, 
and consequently water cught to be decomposed to furnish | proportion. If only 
so much oxalic acid were formed as is proportional to the oxygen in the tartaric 
acid, then 2-3ds of a proportion of carbon would remain, which might form a pare 
ticular compound with the hydrogen ; and for | proportion of tartaric acid, 12 of 
oxalic acid would be produced. In place of this last quantity, I have obtained 
4 oxalic acid, but I have not discovered any hydrogenated compound. Finally, 
it was possible that a peculiar acid had been formed by the carbon, oxygen, and 
hydrogen. This point deserves particular examination, and I should have un- 
dertaken it in the vacations, if I had had time, but hope to resume the. a 
shortly. 
I shall conclude by describing a very elegant method of transforming tartar 
into oxalate of potassa. It consists in dissolving rough tartar in water, with a 
proper quantity of potash or soda, and making the solution pass by means of a 
pump in a continual current through a thick tube of iron or bronze heated to 
400° or 450° F. The pressure need not be more than 25 atmospheres, for no 
gas will be disengaged. A valve is to be placed at the oppesite noe to 
that at which the solution enters, and charged with sufficient weight to obtain 
this pressure ; it will then only be opened by the pressure exerted by the injec- 
tion pump. I have not asyet tried this process, which is also app plicable to other 
substances, but I see nothing which can prevent its success. According to some 
experiments which I have made, less than a proportion of potassa for a “pepor- 
tion of neutral tartar will be necessary.— Ann. de Chimie. 
Distinctive Characters of Tannin and Gallic Acid.—To determine the dif- 
ferent properties of these substances, M. Pfaff employed them of the greatest 
purity, and he obtained the following results. -In a dilute solution of gold, 
gallic acid gives a blue greenish colour, which appears brown by reflected light, 
and the gold is perfectly reduced. Tannin merely reduces the gold to’ a lower 
state of oxidation, and the liquor becomes purple. Gallic acid a faint yellowish 
tint in the solutions of titanium. Tannin precipitates orange-red flocculi. 
Tannin precipitates tartarized antimony white, but gallie acid occasions only 
slight turbidness after a considerable time. Gallic acid renders the caustie 
alkalies brown ; the colour which it produces with the carbonated alkalies is at 
first yellow, with a brownish tint, but it EREDINES soon of a deep green. ‘Tannin 
is Bees patee by the pure and carbonated alkalies, and the liquor becomes brown, 
without changing to green. The salts of morphia, strychniv, quina, and cineca 
honia, are not precipitated by gaillic acid, but they are by tannin. -In ‘its 
combination with the alkalies, tannin seems to undergo a change, which ap- 
proximates it to gallic acid. The scum of coffee owes its property of turning the 
white of egg green, with the influence of the air, to the galic acil which it con- 
tains ; and the white of egg appears to produce this effect by the carbonate of 
soda which enters into its composition. M. Pfaff did not find any gallic acid in 
the plants which contain emetin and veratria.—Schweigger’s Annals, Journaé 
de- Pharmacie, Aug. 1829. “Wag 
On the Copper-Coloured Light Reflected from the Dark Part ef the Moen’s 
Disc. ; by Dr. Burney.—In the evenings of October 30th and SIst, the non- 
iuminatcd part of the moon’s disc, when near the horizon, reflectéd a dull copper 
colour ; a circumstance thai often happens while the sun, or rather the earth, is 
passing through the southern signs of the eciiptic, but seldom, if ever, while pass- 
