PREPARATION OF ALDEHYDE AND ACETIC ACID. 295 
fication, be employed in class-room experiments and in 
testing for silver. 
A few drops of this liquid, added in a test tube to a so- 
lution of nitrate of silver previously curdled by ammonia, 
quickly converts the oxide into metallic silver, which at- 
taches itself as a brilliant coating to the glass. In de- 
scribing this characteristic property of aldehyde, Liebig and 
others appear to regard the application of heat to the mix- 
ture as necessary to the effect, (Chem. Org., p. 377.) We 
have found however that the aldehydic liquid of the above 
process, as well as the more concentrated aldehyde pro- 
cured from it by distillation over chloride of calcium, causes 
a complete and brilliant reduction of the oxide of silver in 
a few seconds at ordinary temperature, and that the same 
effect results even when the tube is immersed in snow, but 
in this case the change requires two or three minutes for 
its completion. 
Heated with hydrate of potassa the liquid becomes yel- 
low, then of a deep reddish brown colour, and in a little 
while yields floating flakes of the characteristic resin of al- 
dehyde. 
On adding to the liquid an excess of caustic baryta in the 
cold, little or no action is manifested ; but as soon as heat 
is applied, the mixture assumes an intense opaque yellow 
colour like that of chromate of lead, which by continuing 
the heat passes into a deep rich brown, as in the preceding 
experiment. 
The proportion of aldehyde in the liquid as it comes from 
the receiver in the above process, is such, that to prepare 
aldehydite of ammonia, we may dispense with the two 
successive distillations from the chloride of lime directed by 
Liebig, and use the fresh product at once for this purpose. 
We therefore add to the liquid about half its bulk of sul- 
phuric ether, and pass a stream of ammonia into the mix- 
ture. As the aldehyde becomes saturated, the compound 
in question falls in an abundant deposit of brilliant trans- 
