34 Improvements in Physical Science [Jan. 
During the drying of these oxalates, the hydrogen of the acid 
must combine with oxygen, and form water. The weight of the 
water thus formed would be 1°125, or about 24 per cent. of the 
weight of the acid. The residual carbon and oxygen would be in 
the proportions proper for forming carbonic oxide. It would be im- 
possible to resolve them into carbonic acid and carbonic oxide. 
Dobereiner conceives the hydrogen not to be an essential constituent 
of oxalic acid. But Dulong’s experiments show us that hydrogen 
is invariably present. Oxalic acid has the property of reducing cer- 
tain metallic oxides to the metallic state. In these cases water 
always makes its appearance during the decomposition of the acid. 
Were it not for the loss of weight stated to take place when oxalate 
of zine and oxalate of lead are heated, it would be easy to explain 
the phenomena observed by Dulong. When the metallic oxide is 
not altered, the oxalic acid is resolved by heat into carbonic acid 
and carbonic oxide and hydrogen; but the hydrogen, in conse- 
quence of its small quantity, would escape detection. When the 
metallic oxide is decomposed, it supplies oxygen to the hydrogen of 
the acid, and converts it into water. 
When a solution of oxalic acid in water is digested over black 
oxide of manganese, Dobereiner found that carbonic acid gas is 
given out. When sulphuric acid is poured upon the liquid, an ad- 
ditional quantity of carbonic acid is driven off. The carbonic acid 
thus formed is greater in weight than the whole of the oxalic acid 
employed. In this experiment the black oxide gives out sufficient 
oxygen to convert the hydrogen into water, and the whole of the 
carbon into carbonic acid. 
2. Agua Regia.—It has been generally supposed that aqua regia 
is a new acid formed by the combination of muriatic acid with nitric 
acid. But Sir H. Davy has lately examined the subject experiment- 
ally, and shown that this opinion is not well founded. When the 
two acids are mixed, they mutually decompose each other, water Is 
formed, and chlorine and nitrous acid evolved. It is the chlorine 
thus disengaged that combines with gold and platinum, and occa- 
sions their solution. (Journal of the Royal Institution, i. 67.) 
3. Acids of Phosphorus—The acids formed by the combination 
of phosphorus with oxygen are of so difficult investigation, that 
hitherto we are but imperfectly acquainted with their composition. 
But the subject has lately attracted the attention of chemists in 
general; and so many persons have engaged in the investigation, 
that it cannot much longer remain incomplete. Two very curious 
and important papers have been published in the second volume of 
the Ann. de Chim. et Phys., the first by M. Dulong, the second by 
Professor Berzelius, 
M. Dulong announces the existence of no fewer than four acids 
composed of oxygen and phosphorus, one of which he has had the 
honour of discovering himself. These acids he distinguishes by the 
following names: hypophosphorous acid, phosphorous acid, phos- 
phatie acid, and phosphoric acid. 
