PREPARATION OF ALDEHYDE AND ACETIC ACID. 293 
presence of the aldehyde is readily shown by adding a few- 
drops of the liquid to a solution of nitrate of silver previ- 
ously curdled by ammonia, and then gently heating the 
mixture. The oxide is speedily reduced, forming a brilliant 
metallic coating on the sides of the glass. 
Substituting for the chromic acid of this experiment, a 
mixture of bichromate of potassa and sulphuric acid, and 
blending with this a quantity of common alcohol, the re- 
action is extremely violent, a large volume of carbonic acid 
is evolved, and the liquid which distils over, contains, with 
other products, much aldehyde and acetic acid. To obtain 
either of these substances but little mingled with the rest, 
special attention must be paid to the proportions in which 
the bichromate, sulphuric acid, and alcohol are mixed, and 
to the order in which they are brought together. Thus, in 
all our experiments, we found, that when alcohol is added 
in small quantities at a time to a mixture of the bichro- 
mate and sulphuric acid the distilled product is almost pure 
acetic acid,hul when sulphuric acid is slowly dropped 
into a mixture of the saltj and alcohol, the liquid which 
passes over contains little else than aldehyde. 
This remarkable difference in the products is, we think, 
readily explained by the different intensity of the oxidating 
power in the two cases. In the former, the alcohol, as it 
falls into the mixture of bichromate and sulphuric acid, 
being surrounded on all sides by free chromic acid, is carried 
rapidly through the lower stages of oxidation, correspond- 
ing to aldehyde and aldehydic acid, until by the addition in 
all of 4 equivalents of oxygen, and the elimination of 2 
equivalents of water, it is converted into acetic acid. In the 
latter case, the sulphuric acid, dropping slowly into the 
mixture of alcohol and bichromate, liberates but a small 
quantity of chromic acid at any one time, and thus, 
limits the oxidation of the alcohol in great part to th© first 
stage, or that of the formation of aldehyde. 
From the observation of these facts, we were led, after a* 
27* 
