Nature of certain Solutions. 95 



carbonate also dried, and absolute alcohol, scarcely a trace 

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

 colours, and the brown colour of the salt is retained. The 

 addition of a little water brings on rapid action. The dull 

 brown colour 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 neces- 

 sary to first form and then decompose herapathite, or whether 

 a suitable test solution could not be obtained by simply acting 

 on quinia with iodine. An iodine solution instantly produces 

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

 brown colour, 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 sul- 

 phuric 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 abso- 

 lutely no excess of either quinia or iodine. But however 

 carefully we may attempt to mix quinia and iodine, we shall 

 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 alka- 

 loid. On the other hand, if iodine is present in excess, the 

 first action is to form one of the more highly iodized 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. 



In a Griffin's beaker place 100 cub. centim. of alcohol of 

 95 per cent., add 5 grammes of quinia sulphate and 40 cub. 

 centim. of acetic acid of 50 per cent. Take dilute sulphuric 

 acid containing one tenth by weight of acid and add of this 

 7 cub. centim. Place the beaker in a water-bath and apply 

 heat till the alcohol begins to boil gently, then add with con- 



