300 



Rosenheim and Tebb 



We were; however, able to find the correct explanation for this dis- 

 crepancy, which by itself proves the indefinite composition of " protagon." 

 By carrying out a tedious series of systematic recrystallisations, constantly 

 controlled by analysis, we have found out the exact conditions under which 

 the phosphorus percentage of " protagon " remains approximately constant. 

 Wilson and Cramer seem to have arrived at this result empirically 

 without, however, recognising or stating the true conditions. These depend 

 in no way on the time of heating and the supposed decomposition, but 

 simply on the proportion of "protagon" to alcohol employed. Wilson 

 and Cramer favoured evidently a very small proportion, as is indicated 

 in the paper by Lochhead and Cramer.^ We found that, by limiting the 

 amount of alcohol used for recrystallisation to a minimum (" protagon " : 

 alcohol = 1:5 for the first and 1 : 2 or less for the subsequent recrystallisa- 

 tions), we were able to keep the phosphorus percentage at the figure held 

 by Wilson and Cramer to be characteristic for "protagon." 



It is obvious that these are not the conditions which favour the intended 

 purification. When using reasonable amounts of solvent for this purpose, 

 as in the preceding series of recrystallisations, it will be seen that 

 " protagon " undergoes a complete change of composition. 



We again quote only one typical experiment, in which another sample 

 of Wilson and Cramer's "protagon" was employed. The same pre- 

 cautions were taken during its preparation and recrystallisation as indi- 

 cated above, the only altered factor being the proportion of " protagon " 

 to alcohol. The results were as follows : — 



Even here a distinct drop in the phosphorus percentage is noticeable, but 

 owing to the whole of the dissolved substance being precipitated again 

 by cooling on ice, no eflBcient separation of the constituents can possibly 

 take place. ^ 



The above results, which agree with those of Wilson and Cramer, 



1 Biochem. Journ., ii., 1907, p. 350. See also Cramer's letter to Posner and Gies, 

 publisTied by the latter in Journ. Biol. Chem., i., 1905-6, p. 79. 



^ We should like to point out that the term " recrystallisation " is hardly justified in 

 this case, as the product precipitated from its hot solution by cooling on ice is amorphous. 

 "Protagon" can only be obtained in crystalline form, according to Liebreich and 

 Gamgee, if the temperature is allowed to fall very gradually. Under these conditions 

 " protagon " would, however, be decomposed in Wilson and Cramer's sense. According 

 to Gamgee and Blankenhorn (Zeitschr. f. physiol. Chem., iii., 1879, p. 277), their 

 best result was obtained when the temperature fell in seventeen hours from 41-25° to 27-5°. 



