Duclaux found that acetic acid is formed in small quantities during fermentation; aldehyde has also been detected.
According to this theory a " chemical type " embraced compounds containing the same number of equivalents combined in a like manner and exhibiting similar properties; thus acetic and trichloracetic acids, aldehyde and chloral, marsh gas and chloroform are pairs of compounds referable to the same type.
The thermal effect of the aldehyde group has the average value 64.88 calories, i.e.
They are hydrolysed by dilute mineral acids yielding hydroxylamine and the parent aldehyde or ketone.
The aldehyde group reacts with hydrocyanic acid to produce two stereo-isomeric cyanhydrins; this isomerism is due to the conversion of an originally non-asymmetric carbon atom into an asymmetric one.
