164 Dr. Herapath on the Optical Properties of 



2nd. It was found that by treating solutions of each alkaloid 

 in a precisely similar manner with iodine, crystals possessing 

 the peculiar properties were only produced in the solution of the 

 pure disulphate of quinine. 



The disulphate of cinchonine solution was merely slightly 

 reddened upon the addition of iodine ; becoming turbid, a cin- 

 namon-brown precipitate falling, which upon heating in contact 

 with the mother-liquid became indigo-coloured, and did not re- 

 dissolve. No crystals were produced. 



Therefore it became probable that iodine, sulphuric acid, and 

 quinine, were absolutely necessary for the production of these 

 crystals. 



1st. To decide the question whether the sulphuric acid was 

 absolutely essential, a portion of the crystals was dissolved in 

 acetic acid, and whilst hot, acetate of baryta was dropped in until 

 no further precipitation occurred ; the solution was filtered whilst 

 hot, and upon cooling there was no appearance of any crystalli- 

 zation after remaining several days. 



2nd. Another portion of these crystals was dissolved by boiling 

 n rectified spirit ; a sherry wine-coloured fluid resulted ; it was 

 divided into two portions. 



(A.) The first was allowed to cool spontaneously ; the crystals 

 were deposited again, but in rosettes, as before described. 



(B.) The second portion of the alcoholic solution was treated 

 whilst hot with acetate of baryta; the sulphate precipitated 

 directly; the supernatant fluid on cooling remained perfectly 

 transparent, and no crystals formed after some days. 



3rd. An alcoholic solution of the pure alkaloid quinine was 

 carefully prepared, and an alcoholic solution of iodine added; a 

 sherry wine-coloured fluid resulted ; no crystals were deposited ; 

 and upon spontaneous evaporation an ochry-yellow precipitate 

 remained, without crystalline form, and having a very resinous 

 appearance. 



Therefore it now became evident that iodine, sulphuric acid, 

 and quinine, were the constituent elements of this peculiar body. 

 How associated, it is difficult to say; but it is probable that 

 they are arranged as a binary compound, the disulphate of qui- 

 nine acting as a feebly electro-positive base to the iodine as ah 

 electro-negative. It is conjectured therefore to be an iodide of 

 the disulphate of quinine. 



It now became an interesting question to decide whether any 

 other of the vegetable alkaloids would act in a similar manner 

 with iodine. The same experiments were tried with the salts of 

 morphine, brucine, strychnine, salicine and cinchonine, but with- 

 out success ; we may therefore almost confidently depend on the 

 production of these crystals being indicative of the presence of 



