90 Mr. M. Carey Lea on the 



not necessary that the combined sulphuric acid should be 

 united to a strong base, neutral sulphates of weak bases are 

 wholly without action. Thus neither brucia nor quinia sulphate 

 causes formation of herapathite ; the sulphuric acid in these 

 salts has no more tendency to bring about the reaction than, 

 for example, that in sodium sulphate. The fact that quinia 

 sulphate does not form herapathite with the test indicates that 

 there is no free iodine present, thus confirming the view that 

 the iodoquinia molecule is not broken up. 



Space cannot be spared here to go with detail into the 

 chemistry of iodoquinia compounds. The whole series of acid 

 persulphates has been most thoroughly studied by Jorgensen *, 

 who distinguishes seven compounds of quinia, sulphuric acid, 

 and iodine, of which four belong to the herapathite type ; that 

 is, they contain three molecules of sulphuric acid to four of 

 quinia and two of hydriodic acid, with increasing amounts of 

 iodine. Putting Ch for C 20 H 2i N 2 O 2 , the composition of these 

 four salts may be taken as 



4Ch, 3H 2 S0 4 , 2HI, I„ 

 4Ch, 3H 2 S0 4 , 2HI, I 5 , 

 4Ch, 3H 2 S0 4 , 2HI, I 6 , 

 4Ch, 3H 2 S0 4 , 2HI, I 7 . 



The first of which series is herapathite. All are isomorphous 

 (I. c. p. 253). Jorgensen's view of the constitution of hera- 

 pathite is that it is " half superiodide, half sulphate; " he gives 

 as its rational formula— 



J 2 J . HChH . . S0 2 . HChH . . S0 2 . HChH . . 

 S0 2 .O.HChH.JJ 2 . 



It appears, however, that the sulphuric acid may be re- 

 moved not only by barium carbonate, but by its hydrate, 

 without breaking up the molecule. It is easily shown that 

 the solution of herapathite, after treatment even with barium 

 carbonate, contains no sulphuric acid. This may be proved 

 by adding to the solution after the treatment ammonia till 

 it becomes pale yellow, evaporating to dryness, and then 

 warming with very dilute hydrochloric acid. An aqueous 

 solution of barium chloride then gives no precipitate, nor 

 even any troubling by standing. It seems perhaps doubtful 

 if a substance having the constitution indicated by the rational 

 formula above cited could have its molecule subsist unbroken 

 after the removal of the sulphuric acid. 



The application of this test leads to the following con- 

 clusions : — 



* Journal fur praktische Chem. (2) xiv. p. 213 ff . 



