v DECOMPOSITION PRODUCTS 227 



The reaction takes place according to the following 

 equation : 



C 2 H 5 OH + 6NaOH + 81 = 5H 2 O + 5NaI + HCOONa + C HT 3 . 



Although this reaction is very sensitive, it has the dis- 

 advantage that it takes place, not only with alcohol, but also 

 with a whole series of other substances, such as acetone, alde- 

 hyde, grape sugar, lactic acid, substances which contain the 

 group CH 2 CO. Lactic acid is not, as was formerly thought, 

 an entirely non-volatile acid, but is partly volatile. A feeble 

 reaction is therefore not a proof that alcohol is really present. 

 Perfectly fresh drawn normal milk also gives a distinct but 

 faint iodoform reaction, as the author has repeatedly proved. 



Another qualitative method for detecting alcohol consists in 

 adding dilute sulphuric acid to the distillate mentioned above, 

 and then a small crystal of potassium bichromate. On warming 

 gently, acetaldehyde, CH 3 'CHO, is given off, which blackens a 

 strip of filter-paper moistened with an ammoniacal silver 

 solution. 1 



A third method is to shake the liquid with benzoyl chloride 

 and caustic soda, which causes the formation of ethyl benzoate, 

 characterised by its odour, if alcohol is present. 



Duclaux 2 has devised a quantitative method for the determi- 

 nation of small quantities of alcohol, which is based upon the 

 smaller surface tension of alcohol as compared with water. 

 Mixtures of alcohol and water have naturally a lower surface 

 tension than pure water. If, therefore, a given volume of 

 alcohol and water is allowed to flow from a capillary opening, 

 the number of drops at a given temperature is constant for the 

 mixture, and with an increasing proportion of alcohol the 

 number of drops increases. Duclaux makes use of a so-called 

 " compte-gouttes " (a drop counter) which consists of a 5 c.c. 

 pipette provided with a capillary tube sufficiently long to allow 

 of the liquid issuing in drops. The capillary opening is so 

 adjusted that when the pipette is filled with water at 15 C. 

 it empties in 100 drops. When an alcohol-containing liquid is 

 to be tested, the pipette is filled to the mark, the outlet, which 

 must be free from every trace of fat, carefully cleaned with 

 filter-paper, and the pipette placed in a suitable holder. The 



1 See under " Determination of Degree of Oxidation of Butter," p. 232. 



2 Traite de Microbiologie. Vol. Ill, p. 7. 



Q2 



