■jS PLANT RESPIRATION 



well as acid, volatile plant compounds, which could pass over 

 into the first distillate, are removed by the distillation from acid 

 or alkaline solutions. In addition acetaldehyde, which is prob- 

 ably to be regarded as a forerunner (Vorstufe) of alcohol, is 

 sometimes formed in anaerobic respiration.^ To be sure, the 

 amounts of aldehyde are trifling at the most, but inaccuracies 

 often beyond the limits of error of the analytical methods are 

 introduced by the presence of acetaldehyde. 



Kostychev has found that the removal of acetaldehyde is 

 absolutely necessary if the aldehyde content rises to at least 0.05 

 the alcohol content. The removal of acetaldehyde is accom- 

 plished as follows according to Kostychev. ^ 50 cc. of a diluted 

 solution of alcohol (as used for quantitative determinations 

 according to Nicloux or Barendrecht) are allowed to stand 15 

 to 20 minutes with the addition of about 10 cc. of a concen- 

 trated solution on NaHSOs- Then the mixture is distilled on 

 the water bath at 30 to 35° with about 15 mm. pressure. In 

 doing this, as long a condenser as possible is used and the 

 receiver is cooled with ice. The adapter of the condenser 

 must be placed within the cooled part of the receiver. If this 

 precaution is not observed small losses of alcohol are not always 

 prevented. To protect the rubber tubing, the receiver is first 

 treated with a small quantity of caustic soda solution, because 

 some SO2 escapes during the distillation. The distillation can 

 be discontinued after about 20 cc. of distillate has passed over 

 into the receiver. The distillate is treated with about 40 cc. 

 of distilled water. It is made certain that the liquid is alkaline 

 in reaction (if not, caustic soda is added), and the mixture is 

 rectified at the usual pressure, for which a measuring flask of 

 50 cc. capacity is used as a receiver, the flask being filled to the 

 mark with distilled water after stopping the distillation. 

 Numerous control analyses showed that no alcohol is lost in the 

 purification just described and the aldehyde is entirely removed. 

 The last distillate can be used directly for the determination of 

 alcohol according to Nicloux. 



1 Cf. e.g. Kostytschew, S., Hubbenet, E. und A. Scheloumow. Z. f. physiol. Chem. 83 : 

 105. 1913. [cf. also editorial note on page 62.) 



2 Kostytschew, S. Bull, de I'acad. des sciences de Petersbourg. IQIS: 327; Biochem. Z. 

 64: 237- 1914- 



