Robertson. — Detection and Estimation of Alkaloids. 51 



Art. X. — The Detection and Estimation of the Alkaloids by 

 means of their Double Sulphocyanides. 



By P. W. Robertson, M.A., Rhodes Scholar. 



[Read before the Wellington Philosophical Society, 3rd May, 1905.] 



The late Mr. Skey, who has enriched the Transactions of the 

 New Zealand Institute by a large number of papers on 

 chemical and physical subjects, has drawn attention to the 

 fact that solutions containing certain alkaloids yield precipi- 

 tates when treated with arnmonium-sulphocyanide and a zinc 

 or mercury salt. Neither the discoverer of the reaction nor 

 any subsequent observer appears to have further investigated 

 these insoluble precipitates. Consequently, at the suggestion 

 of Professor Easterfield, the following investigation was made, 

 with the twofold object of determining the nature of the 

 reaction and of basing upon it a convenient method of 

 volumetric analysis. 



The more important alkaloids were examined, and it was 

 found that in the presence of ammonium-sulphocyanide not 

 only zinc and mercury but many other metals gave insoluble 

 precipitates. In particular the cobalt compounds are cha- 

 racterized by the display of colour which occurs during 

 the precipitation. This forms an excellent test for detecting 

 small quantities of antipyrine. If a solution containing cobalt- 

 nitrate and ammonium-sulphocyanide is added to a liquid in 

 which the drug is dissolved, there first appears a dark-blue 

 precipitate, and the colour of the solution gradually changes 

 through various shades of purple till it finally becomes red. 

 Not only is this reaction as sensitive and characteristic as the 

 ordinary tests for antipyrine, but in addition it possesses the 

 advantage that it takes only a short time to perform. 



Nickel also gives characteristic green precipitates with 

 quinine and cocaine, but the reaction is not so sensitive as 

 was found to be the case with cobalt. The other metals 

 examined, with the exception of tin, give for the most part 

 only faint precipitates. 



The results are collected in Table I, and in the case of the 

 more sensitive reactions the limit of dilution at which the 

 precipitation occurs with excess of the reagents is also given. 



