ANAEROBIC RESPIRATION 75 



II. Formation of the Ethyl Ester of p-Nitro -benzoic Acid.^ — 



The alcohol is shaken with p-nitro-benzoyl chloride in alkahne 

 solution and the resultant ester is recrystallized first from gaso- 

 hne and then from benzene. The melting point is 57^. The 

 nitrogen in the resulting pure product is determined according 

 to Dumas. 



III. Formation of Acetaldehyde-p-nitrophenyl-hydrazone.^ — 

 The alcohol is oxidised to acetaldehyde'- and the latter precipi- 

 tated in the cold with an acetic acid solution of p-nitrophenyl- 

 hydrazine. The yellow precipitate is recrystaUized from 50% 

 alcohol and the nitrogen content of the resulting product is 

 determined according to Dumas. Since acetaldehyde is 

 formed by oxidation not only from ethyl alcohol but also from 

 some other substances, both of the above described methods 

 (I and II) of identification are always preferable. 



The following methods of quantitative determination of 

 alcohol are recommended for studies of anaerobic respiration: 



I. PHYSICAL METHODS 



1. Pycnometric Determination. — The last distillate is col- 

 lected in a small weighed flask and the weight of the entire 

 solution of alcohol is obtained by a second weighing. Then the 

 specific gravity of the distillate is determined and the percent- 

 age content of ethyl alcohol is calculated according to tables at 

 hand. The amount of absolute alcohol may also be obtained 

 by a simple recalculation. 



2. Cryoscopic Determination.^ — This is more reliable and 

 less detailed than the pycnometric determination. The 

 freezing point of the alcohoHc solution is ascertained, from which 

 the alcohol content results by a simple calculation. For the 

 details consult the original paper by Gaunt. The noted Beck- 

 mann apparatus for the determination of molecular weights is 

 useful for determining the freezing point depression. 



3. Stalagmometric Determination.^ — This method is also 

 supposed to be very practical. It is based on the fact that 



1 Buchner, E. und J. Meisenheimer. Ber. d. chem. Ges. 38: 624. 1905. 



- Deniges, G. loc. cil. 



3 Gaunt, R. Z f. analyt. Chem. 44: 106. 1905. 



