294 PREPARATION OF ALDEHYDE AND ACETIC ACID. 
number of comparative trials, to the following process for 
the preparation of aldehyde. 
Equal weights of powdered bichromate of potassa and 
alcohol^ sp. gr. 0,842 being placed in a capacious retort, 
connected with a receiver and the usual means of refrigera- 
tion, we adapt to the tubulure a pipette, charged with sul- 
phuric acid, and whose stem reaches nearly to the surface 
of the liquid, the top of the pipette being furnished with a 
strong gum-elastic bag for injecting the^acid into the mixture 
beneath. We now slowly add the acid, taking care to 
avoid excessive reaction, by sometimes allowing it merely 
to drop spontaneously from the pipette, and again when 
the action subsides accelerating its flow by pressure. At 
this period of the operation, the heat evolved in the retort 
is sufficient to carry over into the receiver a considerable 
volume of the aldehydic liquid ; and, as much carbonic acid 
is at the same time disengaged, the tubulure of the receiver 
should only be loosely closed. Having thus added gradu- 
ally a weight of sulphuric acid equal to about \h times that 
of the bichromate, we apply a gentle lamp heat and con- 
tinue the distillation as long as the aldehydic liquid passes 
over. When the reaction is most energetic, white fumes 
are evolved, which, falling from the beak of the retort into 
the receiver, are so dense that they may readily be poured 
from the latter through a funnel into a narrow necked 
bottle. These, when condensed, form a clear liquid con- 
sisting chiefly of aldehyde. 
By this process 1500 grains of bichromate of potassa and 
the same amount of alcohol have on repeated occasions 
fielded us about 8 cubic inches of a clear liquid, contain- 
ing but slight traces of acetic acid or other extraneous 
matters, and possessing all the characters of a nearly pure 
mixture of aldehyde and water. 
The product thus obtained is sufficiently rich in aldehyde- 
to exhibit instantly and strikingly all the characteristic re- 
actions of that substance. It may, therefore, without recti*- 
