480 M. C. Lea — Nature of Certain Solutions 



quantity forming a deep sherry wine-colored liquid. This solu- 

 tion when allowed to dry spontaneously leaves an amber-col- 

 ored varnish without a trace of crystallization. If, however, 

 we add to this solution a minute quantity of sulphuric acid 

 there is left behind on evaporating a characteristic bluish black 

 film and isolated crystals of iodo-quinia sulphate. In forming 

 this reagent it is more convenient to employ barium carbonate 

 as the decomposition is effected equally well and with it we 

 are certain that the solution contains no barium compound. 

 Barium carbonate decomposes iodo-quinia sulphate with slow 

 disengagement of carbonic anhydride, it seems therefore proba- 

 ble that the resulting solution contains a free base. 



From this solution the sulphate is regenerated with great 

 facility by free, but not by combined sulphuric acid. And as 

 the herapathite thus formed is a well characterized substance 

 we obtain a most useful means of deciding as to whether sul- 

 phuric acid in certain solutions is free or combined. It is 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 sul- 

 phate 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 chem- 

 istry of iodoquinia compounds. The whole series of acid per- 

 sulphates 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 24 N 2 O 2 , the composition of these 

 four salts may be taken as 



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

 4Ch, 3H„S0 4 , 2HI, I. 

 4Ch, 3H„"S0 4 , 2HI, 1° 

 4Ch, 3H" 2 S0 4 , 2HI, L 



The first of which series is herapathite. All are isomor- 

 phous (1. c. p. 253). Jorgensen's view of the constitution of 

 herapathite is that it is " half superiodide, half sulphate " he 

 gives as its rational formula : 



* Journal fur praktische Chem., II, xiv. 213 fE. 



