Eobertson. — Detection and Estimation of Alkaloids. 55 



phate. Concordant results were obtained at different dilu- 

 tions, and in the presence of varying amounts of nitric acid, 

 zinc -sulphate, and ammonium -sulphocyanide, provided that 

 excess was present. 



The results obtained with a decinormal solution of quinine 

 are given in Table II. 



Table II. — Showing the Number of Equivalents of Zinc 

 and Sulphocyanide added to One Equivalent of Quinine, 

 the Number of Equivalents of Sulphocyanide removed by 

 the Quinine, and the Total Volume of the Solution. 



Sul P h0 " Total Sul(,h °' 



TT , cvanide 



Volume - removed. 



30 35 ::: 



30 35* 



40 3-4 



40 3-55 



60 3-45 



60 3-5 



a number of closely concordant 

 experiments in solutions with varying amounts of nitric acid. 



Similar results were obtained by working with normal 

 potassium-sulphocyanide and washing the precipitate with a 

 solution containing zinc and potassium ions. 



From these experiments it appears that one equivalent of 

 quinine combines with three and a half equivalents of sulpho- 

 cyanide to form the double salt — i.e., 3-5 c.c. N sulphocyanide 

 precipitates 0324 gram quinine .*. 1 c.c. N sulphocyanide pre- 

 cipitates 0-093 gram quinine. This method can thus be used 

 for the quantitative estimation of quinine, and it has the great 

 advantage that the whole determination can be performed in a 

 few minutes. 



Although cinchonine and cinchonidine do not form such 

 insoluble precipitates as quinine, nevertheless these alkaloids 

 can be satisfactorily determined in a similar manner. 



Below is given the sensitiveness of the cinchona alkaloids 

 in the presence of zinc-sulphate and (a) ammonium-sulpho- 

 cyanide, (b) potassium-sulphocyanide, at ordinary tempera- 

 tures. 



Quinine. Cinchunine. Cinchonidine. 



Ammonium 1 : 50,000 1 : 25,000 1 : 15,000 

 Potassium 1 : 40,000 1 : 20,000 1 : 12,000 

 The ammonium-salts are characterized by being slightly 

 less soluble than the corresponding salts of potassium. 



It was found in the case of cinciionine and cinchonidine 

 that one equivalent of alkaloid requires three equivalents of 

 sulphocyanide for precipitation — i.e., 3 c.c. N sulphocyanide 



