Eobeetsok.— Detection and Estimation oj Alkaloids. 53 



An examination of the above table will show that the 



cinchona alkaloids, and more especially quinine, give the 



most sensitive reactions. A solution of ammonium - sulpho- 



cyanide and zinc - sulphate compares favourably with the 



well-known alkaloidal reagents, as is seen from the following 



data : — 



-r, Limit of Proportion 



Rea 8 ent - of Quinine. 



Zinc-ammonium-sulphocyanide ... 1 : 50,000 



Phosphotungstic acid ... ... 1:100,000 



Mercury-potassium-iodide ... 1 : 90,000 



Potassium-periodide ... ... 1 : 80,000 



Picric acid ... ... ... 1: 40,000 



Phosophomolybdic acid ... 1 : 30,000 

 Chlorine and ammonia (thalleio- 



quin) ... ... ... 1 : 20,000 



Further, it has the advantages — (1) the reagent is easy to 

 prepare ; (2) it is not extremely sensitive to other alkaloids, 

 as is the case with reagents such as phosphotungstic acid, &c. 



Owing to the extreme insolubility of zinc-ammonium- 

 quinine-sulphocyanide, it is evident that the proportion of 

 sulphocyamde in the compound can be found indirectly by 

 determining the excess of sulphocyanide in the filtrate after 

 precipitation. Excess of zinc-sulphate and ammonium-sul- 

 phocyanide, however, should be present, as the precipitate is 

 perceptibly soluble in pure water. 



As the result of a large number of trials under different 

 experimental conditions, the following method of experiment 

 was finally adopted as being the most convenient for examin- 

 ing the nature of the reaction : Owing to the fact that excess 

 of the reagents are necessary to cause complete precipitation, 

 a strong solution of ammonium-sulphocyanide must be added 

 to the quinine. Then, as the excess of sulphocyanide left in 

 solution after the precipitation is too great to be measured 

 conveniently by the usual method of titration, this strong 

 solution is diluted to a known volume, and then an aliquot 

 portion is taken for analysis. 



Ten c.c. of a decinormal solution of quinine dissolved in 

 <iilute nitric acid was treated with excess of zinc-sulphate and 

 10 c.c. of normal ammonium-sulphocyanide. The white floc- 

 culent precipitate, which forms immediately, became coherent 

 on agitation, and was separated by filtration through a Gooch 

 crucible. Such a crucible has a perforated bottom, which is 

 covered to a depth of -Jin. with tightly packed threaded 

 asbestos. The crucible is fitted into a thistle funnel with a 

 piece of rubber tubing, and the funnel is fixed in a flask, 

 as shown in Fig. 1. By the aid of a suction pump liquids can 



