and on a New Means of investigating them. 485 



The weight of the evidence seems therefore to favor com- 

 plete decomposition by solution into neutral salt and free acid. 



When herapathite is dehydrated either by long keeping 

 over oil of vitriol, or by exposure to a temperature of 100° C. 

 for several hours its color changes from green to dark brown 

 and its luster is lost. In this condition it dissolves sparingly 

 in boiling absolute alcohol and separates by cooling in blackish 

 particles which show little trace of crystallization. 



When the brown substance is placed in a vial with barium 

 carbonate also dried, and absolute alcohol, scarcely a trace of 

 action ensues. The liquid, even if kept warm, scarcely colors 

 and the brown color of the salt is retained. The addition of a 

 little water brings on rapid action. The dull brown color 

 changes to bright metallic green and solution goes on steadily 

 as the sulphuric acid is removed by the barium carbonate. 



We thus have the curious result that two substances, both 

 entirely insoluble in water, scarcely act on each other until 

 water is present, and then a rapid decomposition results. 



The question naturally presents itself whether it is necessary 

 to first form and then decompose herapathite or whether a 

 suitable test solution could not be obtained by simply acting 

 on qninia with iodine. An iodine solution instantly produces 

 in one of quinia a bulky precipitate of a light yellowish brown 

 color, quickly redissolving if the solutions were not too strong 

 and the liquid thus obtained if the iodine is not in excess, 

 immediately forms herapathite on the addition of sulphuric 

 acid. 



But the reaction is not a delicate one ; a trace of sulphuric 

 acid cannot be detected as with the solution obtained from 

 herapathite. The reason appears to be as follows : When pure 

 herapathite is used the resulting solution contains absolutely no 

 excess of either quinia or iodine. But, however carefully we 

 may attempt to mix quinia and iodine we will always have a 

 slight excess of one or the other and in either case the delicacy 

 of its reaction is lost. If quinia is present in excess a trace of 

 sulphuric acid is required to saturate it and it has been already 

 mentioned that the test solution will not take sulphuric acid 

 from quinia or from any other alkaloid. On the other hand, 

 if iodine is present in excess the first action is to form one of 

 the more highly iodised bases, more soluble than herapathite 

 and crystallizing less well. So that in either case a trace of 

 sulphuric acid is consumed before the proper reaction occurs 

 and if only a trace is present the reaction may fail. 



It is better therefore to prepare herapathite in the first place 

 and a convenient means of obtaining it will be here given. 



