352 



Prof. H. E. Armstrong and Mr. E. Horton. [Mar. 3, 



The Estimation of Hydrogen Ci/anide. — In most cases the determination of the activity 

 of the enzyme preparations considered in this communication has involved the estimation 

 of hydrogen cyanide ; the method we have adopted is a simplification of that referred to 

 in No. XII of these studies (p. 329). Instead of filtering off the precipitate of silv^er 

 cyanide in the manner there described, after running the measured sample (10 c.c.) into a 

 flask (300 c.c.) containing the solution of silver nitrate (15 c.c. — N/5) and then adding 

 •sodium acetate (15 c.c. — N/5), if benzaldehyde be present we pass steam into the mixture 

 during 2 — 3 minutes until the aldehyde is volatilised and then add to the cooled liquid, 

 ammonia (5 — 10 c.c.) and afterwards a solution of sodium chloride (4 c.c. — N/1). 



The flask is then connected to a condenser and excess of a saturated solution of tartaric 

 acid (about 20 — 25 c.c.) is poured in tlirough a thistle funnel (see figure). The liquid is 



heated to the boiling point and a current of steam passed 

 in during 15 minutes, the distillate being collected in a 

 slight excess of an N/5 solution of caustic potash. The 

 distillate is titrated with an N/20 solution of silver 

 nitrate. An estimation can be effected in 30 minutes. 

 The excessive frothing which often occurs when the 

 liquid is distilled may be prevented by adding a few 

 drops of olive oil. 



To compare the method witli the niodification of 

 Fordos and Gelis' method adopted by Dunstan, Henry 

 and Auld, ajnygdalin was hydrolysed by emulsin and 

 the amount of hydrogen cyanide liberated was then 

 estimated by both methods. 



A solution of 20'451 grammes of amygdalin in 200 c.c. 

 of water containing 10 c.c. of tlie solution of emulsin 

 was kept at 25°. At intervals of (usually) an hour 

 22 c.c. were withdrawn and introduced into a flask con- 

 taining a drop of concentrated sulphuric acid, to stop the 

 action of the enzyme. From this sample two portions, 

 each 10 c.c, were taken : in one the cyanide was estimated 

 as described above ; the other was added to excess of a 

 solution of .sodium hydrogeji carbonate and either 

 titrated directly witli an N/50 sohition of iodine, or it was diluted and an ali<iuot portion 

 titrated. The following results were obtained : — 



Time. 



Volume (c.c.) of 



Weight (gramme) of 

 prussic acid. 



Percentage of hydrolysis. 

















Silver 

 solution. 



Iodine 

 solution. 



From 

 silver. 



F rom 

 iodine. 



From 

 silver. 



From 

 iodine. 



Hours. 

 1 



3i 

 4 

 6 

 « 

 24 



4 15 

 «-95 

 9-6 

 10-7 

 11 -95 



IH -3 



40 -9 

 06 0 

 91 -5 

 94 -5* 

 105 -0* 

 11 1 -5* 

 174 -0 



0 01127 

 0 -01888 • 

 0 02608 

 0 •02i)07 

 0 -03247 



0 04972 



0 01 143 

 0 -01844 

 0 -02557 

 0 •02(i41 

 0 -02935 

 0 -031 Hi 

 0 -04803 



20-9 

 34 -9 

 48-3 

 53 -8 

 60-1 



92 -0 



21 1 

 34 1 



47 -3 



48 -9* 

 54 -3* 

 57 •7* 

 90 -0 



• In these cases the titrations were curried out on the following day ; tlie results are given as 

 showing Unit it is iioccsmiry to titnitc iit onco with iodinp to ohtain correct values. 



