QUINOLINE AS A REAGENT 



QUINOLINE AS A REAGENT 



200 to 100 years ago, who are cited for the istry were chiefly observational: noting the 



beginnings of "microchemistry", were not, constituents in material to be analyzed, and 



primarily, groping for small-scale procedures making identifications by microscopic ap- 



when they turned to the microscope. They pearances existing in the material. The last 



had a much better appreciation of its real use was later extended to identification of 



value. mineral crystals by their properties in polar- 



The uses of the microscope in chemistry ized light, and now is gradually being applied 



comprise at least the following: in chemical science. About a hundred years 



(1) Taking a closer and better look at ago, identification by means of chemical 

 things, and observing their minute charac- microcrystal tests was developed in some 

 teristics, regardless of the amount of mate- aspects, chiefly inorganic and alkaloidal, but 

 rial available. the possibilities here were grossly neglected 



(2) In particular, observing characteris- w^hile chemistry "went quantitative", and 

 tics that cannot be seen at all with the un- still await anything like adequate develop- 

 aided eye: for a century and a quarter now ment. 



this has meant not merely characteristics 



too small to be seen by the unaided eye, but Charles C. Fulton 



also those revealed by polarized light and 



an analyzer, plus compensators and the 



other fittings of the polarizing microscope. 



This use also does not depend on whether Quinoline is a useful reagent in chemical 



much or little material is available. microscopy for detection of a number of cat- 



(3) Making identifications by microscopic ions and as a group reagent for the elements 

 observations and microcrystal tests, for named below. Pure quinoline produces char- 

 which the microscope is essential, again re- acteristic crystals with the solid chloride of 

 gardless of the amount of material available, any single one of the following: divalent 



(4) Using the microscope as an adjunct to cobalt, copper, iron, manganese, mercury, 

 procedures on a small scale. nickel, cadmium, calcium, and zinc, and 



These uses are not mutually exclusive or monovalent copper. When more than one of 

 even distinct; they overlap greatly. There is these chlorides are present, mixed crystal 

 no intention of saying here that the early formation may occur, so additional tests are 

 chemists never thought of the fourth of the needed for confirmation, but the mixed crys- 

 above uses: of course they did, but they had tals formed are still a good indication of 

 primarily in mind the other uses, which which cations are most probably present, 

 modern chemical science seems to have for- When a cation which normally forms a col- 

 gotten, and which most modern chemists ored product with quinoline is involved in 

 disregard or overlook. When the early chem- mixed crystal formation with a cation which 

 ists turned to small-scale procedures it was, normally forms a colorless product, the re- 

 at least as often as not, to adapt them to sultant crystal generally shows the shape of 

 microscopic observation, rather than the the colorless specie and the color of the col- 

 reverse, to adapt the microscope to small- ored specie. WTien two cations which nor- 

 scale chemistry. mally form colored products are involved, 



All the uses apply both to the materials they may form off -colored crystals; heating 



to be analyzed or studied, and to the results will usually develop characteristics which re- 



of chemical reactions, particularly the crys- semble one of the components, 



tals resulting from chemical precipitations. A drop of sample solution which has been 



The earliest uses of the microscope in chem- converted to chlorides is evaporated on a 



57 



