IOWA ACADEMY OF SCIENCES. 
187 
densed acetaldehyde is conducted into a receptacle whose 
tempera.ture should remain below 18°. 
Acetaldehyde is a mobile, peculiar smelling liquid. The 
odor is very penetrating and resembles that of apples 
slightly. It has a specific gravity of 0.8009 at 0°. It is 
miscible in all proportions with water, ether, and alcohol. 
It was given the name ‘‘aldehyde,’^ meaning dehydrated 
alcohol, by Liebig. It has the property of polymerization 
to a marked degree. It is this property that presents one 
of the greatest difficulties, which must be surmounted in 
the synthesis we are considering. The following are some 
of the ways in which polymerization may occur. Small 
quantities of acids or salts, especially zinc chloride and 
sodium acetate convert aldehyde at ordinary temperatures 
into paraldehyde which has the formula ( 021140 ) 3 , the 
change, accomplished with the evolution of heat and con-' 
traction, is particularly rapid if a few drops of sulphuric 
acid are present. Paraldehyde is a colorless liquid boiling 
at 124°, and having a specific gravity of 0.9943 at 20°. It 
has the very peculiar property of being more soluble in cold 
water than in warm. It is used in medicine as a sleep- 
producer. When distilled with sulphuric acid ordinary 
aldehyde is regenerated. 
Metaldehyde is produced by the same reagents as those 
producing foraldehyde, but the temperature is kept below 
0°. It is a white, crystalline body insoluble in water, but 
readily dissolved by hot alcohol and ether. If heated to 
112*^-115°, it sublimes, without previously melting, and 
passes into ordinary aldehyde with only slight decomposi- 
tion. 
The water in the solution of mercuric bromide, previously 
mentioned, will be carried off, after having united with the 
acetylene, as acetaldehyde. The mercuric bromide will re- 
main unchanged. It is therefore necessary to add water 
from time to time and the evolution of acetaldehyde will 
continue as long as the acetylene is conducted into the 
solution. 
