— i55 — 



aldehyde. W. Denis and P. R. Dunbar 1 ) have now published another 

 method intended to serve the same purpose. In this process iocc. 

 of the extract of almonds are mixed with 10 to 15 cc. of a freshly- 

 prepared 10 per cent, phenylhydrazin solution, the liquid shaken, 

 tightly closed, and left to stand in the dark for about 12 hours. Next, 

 200 cc. of cold water are added, and filtered through a Gooch filter- 

 crucible. The precipitate is washed first with cold water and after- 

 wards with 10 cc. of 10 per cent, alcohol, dried for three hours 

 in vacuo at 70 to 8o°, and weighed. The weight found, multiplied 

 by 5,408, gives the number of grammes of benzaldehyde in ioocc. 

 of the solution. Benzoic acid or nitrobenzene have no disturbing effect 

 upon the accuracy of the method. 



The comparative investigations of H. Runne 2 ) into the determ- 

 ination of hydrocyanic acid in bitter almond water supply a very valu- 

 able review and literary index relating to the methods of hydrocyanic- acid 

 determination at present known. From Liebig's first method 3 ) onwards 

 up to the recent colorimetric tests of E. Durieu 4 ), all methods of analysis 

 by weight or volume, together with the suggestions for improvement 

 made in the case of each method, have been checked and are criti- 

 cally discussed by Runne. The author finds Deniges' modification 

 of Liebig's precipitation method to be the most useful and trustworthy 

 test for bitter almond water. Deniges' 5 ) modification consists in using 

 iodide of potassium as an indicator instead of chloride of sodium, as 

 proposed by Liebig, because the silver-salt of iodide of potassium is 

 insoluble in ammonia, and it is thus made possible to carry out the 

 decomposition of the cyanohydrin by the excess of ammonia instead 

 of by potash liquor. In this process the termination of the reaction 

 is shown by turbidity, caused by the iodide of silver eliminated, this 

 being more readi'y noticed in the titrating liquid (since that is already 

 more or less cloudy by itself), than either cyanide or chloride of silver, 

 such as is separated in the original method. By this modification 

 another drawback of Liebig's method is overcome, viz., that owing to 

 the ready solubility of cyanide and chloride of silver in the ammonia 

 which is formed by the decomposition of hydrocyanic acid it is possible 

 that more silver solution may be used up than is accounted for by 

 the actual content of hydrocyanic acid. 



*) Journ. Ind. and Eng. Chem. 1909, p. 256. Through Chem. Ztg. Repert. 

 33 (1909), 281. 



2 ) Apotheker Ztg. 24 (1909)1 288, 297, 306, 314, 325, 333, 344, 356. 



3 ) Liebigs Annalen 77 (1 85 1) 102. 



4 ) Bull. Soc. pharm. 1902, no. 5. 

 8 ) Compt. rend. 117 (1893), 1078. 



