THE METHODS OF MICROCHEMICAL QUALITATIVE ANALYSIS 263 



Behrens 1 has successfully used this procedure in testing for 

 the alkaloid quinine. Although no other practical application 

 of this method of testing has yet been made, its possibilities in 

 organic analysis are great, and the principle upon which the test 

 is based is exceedingly interesting, namely, inducing crystalliza- 

 tion in an amorphous mass through the presence of a mother 

 substance dissolved in a suitable solvent. 



EXPERIMENTS. 



a. Dissolve a little quinine in dilute H 2 SO 4 , add to the drop of solution a 

 fragment of KI, stir until dissolved, then add a fragment of KNO 2 . Decant from 

 the brown amorphous mass, wash the precipitate once with water and dissolve it 

 in C 2 H 6 OH. The alcoholic solution is flowed over a clean previously warmed slide 

 so as to cover it with a thin homogeneous varnish. Examine under the micro- 

 scope and make certain there are no pleochroic crystals. 



Dissolve a little quinine sulphate in dilute HC^sO^ Draw a narrow streak of 

 this solution across the varnished surface. Immediately highly pleochroic crystals 

 of iodo-quinine sulphate (Herapathit) will separate. 



The student should satisfy himself that this is actually an excellent test for 

 quinine, although quinine was employed in making the reagent. Try, for example, 

 pure cinchonine, cinchonamine, etc., in HC 2 HaO 2 solution; no Herapathit crystals 

 will be obtained. 



XI. Testing for the evolution of gas from a substance when treated 

 with a reagent. 



Dissolve in hot freshly drawn distilled water such an amount 

 of pure gelatin (one or two square millimeters of sheet gelatin) 

 that the solution just jells on cooling. It is essential that this 

 jelly shall not possess too high a setting power nor yet be so thin 

 that considerable time is required for it to set after melting. 



The substance to be tested, if a solution, should be evaporated 

 to dryness in a thin film, or if a solid, very finely powdered or 

 spread out in a thin uniform layer. Upon the dry residue a 

 small drop of the melted gelatin is caused to fall, is quickly 

 spread in a thin layer, and the slide allowed to stand upon a cool 

 metal surface until the gelatin sets. The preparation is then 

 placed upon the stage of the microscope and is focused. Next to 

 the jelly drop is placed the reagent whose effect is to be tested, 



1 Anleitung, z. mikro. Anal. v. wichtigsten organ. Verbind. Heft III, 92. 



