514 Scientific Proceedings, Royal Dublin Society. 



In the estimation of volatile acids by distillation the principle underlying 

 the method is that each acid has a definite rate of volatilisation. Duclaux, 

 relying on this principle, devised a method worked ixnder standard con- 

 ditions. He distilled 110 c.c. of a solution containing approximately 1 to 2 

 per cent, of acid. 100 c.c. of distillate were collected in ten fractions of 

 10- c.c. each. By expressing the titration of the fraction as a percentage of 

 the total amount distilled, he was able to obtain a series of constants for each 

 acid, which served to identify the particular acid. This method of Duclaux. 

 or a modification of it, in which the essential features were maintained, has 

 been used by several workers. It has, however, been subjected to much 

 criticism. 



As a result of the distillation of aqueous phenol solutions at constant 

 volume, Naumann and Miiller 1 came to the conclusion that under constant 

 conditions of temperature and pressure, the amount of substance distilling 

 was proportional to the amount of- substance in the flask. They deduced 

 values for the ratio of the amount of acid in the flask to the amount distilling 



doc 

 in each fraction, which they denoted by the symbol -v-, and also for the ratio 



. tl' 



of the titration of a fraction to the one preceding it, which they wrote -=-. 



Co 



Stein' distilled aqueous solutions of certain volatile acids in a current of 

 steam, and observed certain regularities in the distillation. By increasing the 

 length of the carbon chain, the volatility in steam of the saturated fatty acids 

 was increased. In order to study the effect of different groups, substitution 

 products of acetic acid were distilled. The replacement of hydrogen by negative 

 groups resulted in the volatility in steam being lowered, phenyl and chloro 

 groups having less effect than hydroxy or carboxyl groups. Acids containing 

 these latter groups were practically non-volatile. To express the rates of dis- 



1 a 



filiation, values were calculated from the formula - log , where v = volume 



v a - x 



distilled, a = amount of acid originally present, x = amount of acid distilled. 

 Eichmond 3 gives a formula a = 0-4013 x 1-72" where 0*4013 is a certain 

 distillation constant for formic acid. He found that the corresponding 

 constants («) for the next four members of the series could be found by 

 giving n values from 1 to 4. For the higher acids or iso-acids the formula 

 does not appear to hold. A method of steam distillation has also been 

 described by Dyer. 4 For the analysis of mixtures Dyer is the only worker 

 who used the method of distillation at constant volume. He aimed at keep- 

 ing the volume approximately the same by introducing steam. He regulated 



l Beriohte, 1901, 34, 224. c 3 Analyst, 1908, 33, 305. 



3 J. pr. Chera., 1913. 88, 83. 4 J. Biol. Chem., 1917, 28, 445. 



