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Vielhaber's method 1 ) in which magnesium hydrate is used for 

 splitting- up up the cyanohydrin, and chromate of potassium as an indicator, 

 is also, as Runne shows, a thoroughly trustworthy one; but the pre- 

 paration of the hydrate of magnesium (a body which loses some of 

 its strength by keeping and by the absorption of carbon dioxide gas), 

 is perhaps a little too cumbersome to make the process generally 

 popular. It has however been incorporated into the U. S. Ph. for 

 the determination of the hydrocyanic acid content of oil of bitter 

 almonds, and in our laboratory, too, it has yielded the best results 

 in testing oils containing that acid. 



The same subject is dealt with in a paper by G. Guerin and 

 L. Gonet 2 ) which relates especially to Buignet's process 3 ). Buignet's 

 process agrees generally with the older method of C. Mohr 4 ), and also 

 shares its faults. According to both, sulphate of copper is added to 

 an ammoniacal solution of hydrocyanic acid so long as the blue colour 

 persists, in other words, so long as an excess of copper salt is present. 

 But the blue colour is so faint that it is difficult to determine exactly 

 when the reaction has reached its close. Guerin and Gonet recommend 

 a slight addition (0,5 g.) of sodium sulphite to the ammoniacal hydro- 

 cyanic-acid solution, whereby the liquid which has titrated out is said 

 to acquire a brighter and more intense colour. They are, moreover, 

 of opinion that the copper-deposit which is precipitated contains more 

 copper than is accounted for by Buignet's equation. 



CuS0 4 + 4NH 4 CN = (NH 4 ) 2 S0 4 + CuiCN) 2 2NH 4 CN 



Hence, they argue, if 1 cc. = 0,001 g. HCN, the copper solution 

 should contain not 23,09 g. but 30,81 g. of copper sulphate crystals 

 per liter. According to the authors, the reaction takes place as follows: 

 CuS0 4 + 3NH 4 CN === (NH 4 ) 2 S0 4 + Cu(CN) 2 NH 4 CN 



It remains to be seen whether the new suggestions will make the 

 method more popular. 



J. C. Umney 5 ) has dicovered that the by-product in the manu- 

 facture of terpineol which is brought to market under the inappro- 

 priate name of Terpinolene is being used as an adulterant, especially 

 of oil of spike. According to Umney, it is a particularly objectionable 

 addition, because it does not noticeably influence the constants of 

 spike oil, but must be principally detected by its odour, and its 

 presence is therefore liable to escape an analyst who is not quite 

 familiar with the characteristic odour of spike oil. When the spike oil 

 is subjected to fractional distillation the adulterant is found in the parts 



*) Arch, der Pharm. 213 (1878), 408. 



2 ) Journ. de Pharm. et Chim. VI. 29 (1909), 234. 



3 ) Ibidem III. 35 (1859), 168. 



4 ) Liebig's Annalen 94 (1855), 198. 



5 ) Chemist and Druggist 75 (1909), 292. 



