and L. Varetine?) published a Shout notice on the aieve sibieee oy leans 
sulphocyanate reaction, where the acid or the solution of the cyanide i: 
after addition of ammonium sulphide. The presence of formic or acetic acic 
importance. The reaction is so exact that even an amount of sulphocyanic a id cor 
sponding to 0.000054 g. hydrocyanic. acid may be identified thereby, the ‘method hu 
being twenty times more sensitive than the Prussian blue reaction. In order to avo 
losses, the authors?) have designed a modification by using calcium polysulphides 
lieu of ammonium sulphide. It would lead us too far to describe all the particul 
of. the method, and we refer our readers to the original paper; anyhow, since hydr. 
cyanic acid is found frequently in the vegetable kingdom, and occurs sometimes. Whe id 
distilling certain plant stuffs, we wish to take short notice of this Works 
For the identification of hydrocyanic acid, a variety of methods: ms known. jaan ! 
authors, G. W. Anderson*) and I. W. Kolthoff*) deal critically with these methods, . 
starting frown own investigations. According to these authors, the Sennen of 5 
the different reactions is as follows: — i At ae ne a 
Sensitiveness measured id mgrms. CN per litre: — 
Anderson Kolthoff : os Re oe 
Prussian blue reaction . . . 2.4 to 3.9 mgrm. 2 mgrm. per litre 
Thiocyanate reaction. . . . 0.39 mgrm. OTe cae PSN 4 
Pieric “acid teaction..(.\/ja 1: BOh ts: bo ye 
Guajac resin reaction. . . . 0.039 , az O04 5, so uae na i. 
Phenolphthalein reaction . . — 0:4 to 00523, ae 4 
Silver cyanide’ reaction: 2-228: t= bt0. O08 ee 4 
lodine-and-starch reaction . . 0.39 , Oe wie te 4 
~ 
According to these statements, Schonbein and Pagenstecher’s guajac resin reaction 
would appear to be the most sensitive, hence preferable, reaction, but incorrectly, - . 
since (as Kolthoff remarks) this reaction is, generally spoken, not typical. Several 
bodies with oxidizing qualities (e.g., the halogens, ozone) and indifferent substances _ 
(ammonia, cigar smoke) give the reaction likewise. A negative reaction, according to. 
Dragendorff as well as to Anderson, proves the absence of hydrocyanic acid; Koltho 
disapproves of this, as some substances with reducing power inhibit the reaction. a 
Hydrogen sulphide interferes with the phenolphthalein reaction and must b 
removed with a cadmium solution. Inasmuch as chlorine, bromine, and hydroge 
peroxide do not show a red coloration, this reaction is more typical than the precedir 
one; anyhow, larger amounts of the substances mentioned may inhibit the reaction. 
The silver cyanide reaction is not specific for hydrocyanic acid. AN chlorine 
present, the distillation. may be repeated from a solution of borax. — deg 
The iodine-and-starch reaction is neither typical, as several bodies of redu cir 
qualities are likewise capable of binding iodine. If, however, the solution is acidul 
afterwards, a blue coloration may be taken granted as proof for the PiESeye of hy re 
cyanic acid, the reaction being typical with the aqueous distillate. . ; 
The picric acid reaction, generally spoken, is not typical, since it is given by 
substances with reducing power, such as sulphurous aca, ae Ke 
, = = 
1) Journ. d. ‘Pharm. et Chim. VI. 12 (1915), 74. — 2) Ibidem VII. Ww (1917), 97. re 
Industry 36 (1917), 195. — *) Pharm. Weekblad 54 (1917), 1157 spathehee Ztg. 32 (917), 5 es 
