— 154 — 



5 minutes, to titrate again. The calculation is based upon the following 

 equations: 



HCN + KOH = KCN + H 2 O 



C 6 H 5 CHOHCN + KOH = KCN + C 6 H 5 CHO + H 2 O 



2 KCN + HgCl 2 = Hg(CN) 2 + 2 KC1. 



When free hydrocyanic acid in the presence of benzaldehyde cyano- 

 hydrin has to be determined it is not sufficient to dilute the neutralised 

 solution with sublimate and to titrate with alkali,, because in that case 

 the results are always too high, inasmuch as the nitrile is decomposed 

 by the alkali as the latter drops in. In such a case the best mode of 

 procedure is as follows: 



The solution under examination is allowed to run into a separating 

 funnel with about 20 cc. saturated neutral sodium sulphate solution and 

 neutralised after adding 50 cc. ether and 10 drops iodo-eosin solution. 

 Any sodium sulphate which may be precipitated is re-dissolved by 

 adding water. Sublimate solution is next added, the mixture vigorously 

 shaken, and the aqueous liquid separated off into a glass. The solution 

 remaining in the funnel is then extracted once with 20 cc. sodium sulphate 

 solution and again with only a little of the solution. The extracted acid 

 is titrated in the usual way with alkali. 



As a sure method for the detection of free hydrocyanic acid in parts 

 of plants, C. Ravenna and M. Tonegutti 1 ) suggest the immersion of the 

 leaves, for one minute, into highly dilute boiling potash liquor. The tem- 

 perature of the liquid must not be reduced during the immersion. Aft- 

 erwards the alkaline liquid is acidulated with tartaric acid, subjected to 

 steam distillation, and the distillate collected in potash liquor. By applying 

 this method the authors found that, contrary to their previous assumption, 

 the leaves of cherry laurel do not contain free hydrocyanic acid, or contain 

 it only in such minute proportions that it cannot be detected by the ferro- 

 cyanide of iron test. 



Physical Notes. 



In our last Report 2 ) we referred to the lengthy paper by Chr. J. Hansen 

 on the decrease in temperature of high-molecular steam under low pres- 

 sures. In this paper, which is supported by experiments, Hansen entered 

 a decided opposition against statements alleged to have been made by 

 von Rechenberg in the course of the controversy between himself and 

 Hansen 3 ). As Hansen had introduced a fresh point of view into the pole- 



*) Atti R. Accad. dei Lincei, Roma V. 19 (1910), II. 19. Quoted from Chem. Zentralbl. 

 1910, II. 892. 



2 ) Report October 1910, 164. 



3 ) Comp. Report April 1910, 158; October 1910, 164. 



