ON TflE CHEMICAL ASPECTS OF CYANOGENESIS IN PLANTS. 157 



Much experimental work, however, still remains to be done in order 

 to substantiate . the view that the prussic acid originates in the plants 

 from nitrates, and especially to trace the exact mechanism of this process, 

 and also to ascertain the reaction into which the prussic acid subsequently 

 enters and the nature of the compounds formed. 



Dniamic Tsomerisvi. — Report of the Govimittee, consisting of Professor 

 H. E. Armstrong (Chairman), Dr. T. M. Lovvry (Secretanj), Pro- 

 fessor Sydney Young, Dr. J. J. Dorkie, Dr. A. Lapworth, and 

 Dr. M. O. Fokster. (Draicu vp bij the Secretary.) 



Attkntion has been directed during the past two years mainly to the 

 determination of the proportions in which isodynamic compounds are in 

 equilibrium in solution. The method of investigation, which was briefly 

 referred to in the last report,' involves the measurement of the solubility 

 of one of the isomerides, both before and after isomeric change has taken 

 place. Only one of the solid isomerides can persist in stable equilibrium 

 with the solution. This is not necessarily the form which predominates 

 in the liquid ; indeed, the modification which thus persists may vary with 

 the solvent''' and differ in closely related compounds (compare nitro- 

 camphor and its Tr-bromo derivative). The concentration of the original 

 compound is kept substantially constant by stirring the solution with an 

 excess of the solid ; any increase which is observed in the concentration 

 of the saturated solution is attributed to the formation in the liquid of one 

 or more dynamic isomerides. Tf the initial concentration of the saturated 

 solution be A and the final concentration B, the ratio A/B aflTords a 

 measure of the pi-oportion of the original material present in the solution 

 when equilibrium between the dynamic isomerides is attained. 



In applying the method experimentally certain difhculties are 

 encountered. 



(1) When isomeric change occurs rapidly, the products appear in the 

 solution before the latter is saturated with the original material. In 

 such cases it is necessary to make solubility-measurements at frequent 

 intervals during the early stages of the experiment and to deduce the 

 initial value by extrapolation. When, however, isomeric change proceeds 

 slowly or only after the addition of a catalyst, the measurements can be 

 made at leisure and the experimental errors are very greatly reduced. 



(2) Whether isomeric change be rapid or slow, it is essential that the 

 solid u.sed in effecting saturation consist wholly of one isomcride. To 

 ascertain if this be the case, the sample should be extracted at constant 

 temperature with successive quantities of the solvent ; if the material 

 be pure, the different extracts should have equal concentrations. In 

 comparing different series of observations those which give the smallest 

 ratio of initial to final concentration are the more likely to be correct. 



(3) In deducing the pro2)ortion of the original material present in 

 the solution, it has been assumed that the solubility of this form remains 

 constant throughout the experiment and is not affected by the products 

 of isomeric change. This cannot, as a rule, be tested directly, since the 

 method is of greatest value in cases in which the less stable isomerides 

 are unknown or cannot be prepared in a pui'e state. Important evidence 



' Cambridge, 1904, p. 218; compare Lowry, Prvc, 1903, 19, 156. 

 = Dr. Whiteley, ym/M, 189i)i, 75, 231. 



