85 MOUNTING AND LABELING. 



croscope would be far less liable to injury than as if some acid giving off fumes 

 were used. 



198. Herapath's Method of Determining Minute Quantities of Quinine. — For 

 a so-called test fluid 12 c.c. of glacial acetic acid, 4 c.c. of 95 per cent, alcohol and 

 7 drops of dilute sulphuric acid (g 197) are mixed. A drop of the test fluid is put 

 on a slide and a very minute amount of quinine added. After this is dissolved, 

 add an extremely minute drop of an alcoholic solution of iodine. "The first ef- 

 fect is the production of the yellow cinnamon-colored compound of iodine, and 

 quinine which forms as a small circular spot ; the alcohol separates in little drops, 

 which by a sort of repulsive movement, drive the fluid away ; after a time, the 

 acid liquid again flows over the spot, and the polarizing crystals of sulphate of iodo- 

 quinine are slowly pro luced in beautiful rosettes. This succeeds best without the 

 application of heat." Dr. Herapath used this method to determine the presence 

 of quinine in the urine of patients under quinine treatment. See Hogg, p. 150 ; 

 Quarterly Jour. Micr. Sc, vol. ii, pp. 13-18. For farther papers on micro-chem- 

 istry by Dr. Herapath, see the Royal Society's Catalog of Scientific Papers. 



\ 199. List of Substances for the Study of Crystallography with the Micro- 

 scope.* — The substances are crystallized on the cover glass in all cases, and in all 

 cases, except where otherwise stated, a saturated aqueous solution of the substance 

 was first prepared. 



1. Ammonium chloride ; 2. Ammonium copper chloride ; 3. Rarium chloride ; 

 4. Cobalt chloride (Beautiful crystals obtained by mixing the saturated aqueous 

 solution with an equal volume of 95 per cent, alcohol. Crystallization in a cur- 

 rent of dry air some distance above an alcohol or Bunsen flame ; Mount in xylol 

 balsam (|| 176, 191). 5. Copper acetate ; Mount dry (? 170). 6. Copper sulphate. 

 Crystals much more satisfactory when examined in the " mother liquor." 7. Lead 

 nitrate ; S. Mercuric chloride (Corrosive sublimate), mount in xylol balsam ($$ 176, 

 191). 9. Nickel nitrate; obtain crystals by heating. Mount in xylol balsam 

 (?? 186, 191); 10. Potash alum; ir. Potassium chlorate; 12. Potassium dichro- 

 mate. Compare specimen crystallized by heat and spontaneously ; mount dry or 

 in xylol balsam (?£ 170, 176). 13. Potassium iodide. Dilute with one or two vols, 

 water and crystallize by heat. 14. Potassium nitrate ; 15. Potassium oxalate ; 16. Po- 

 tassium sulphate ; 17. Salicine. Fuse the dry saliciue on the cover-glass, mount 

 d r y ($ 17°) ; T 7- Salicylic acid. Make a 10 per cent, solution in 95 per cent, alco- 

 hol. Let it crystallize spontaneously in the air. Mount dry {\ 170) ; iS. Sodium 

 chloride (common salt). Mix sat. aq. sol. with one or two volumes of water, and 

 heat. Mount dry or in balsam (\\ 170, 176). 



\ 200. For directions and hints in micro-chemical work and crystallographv, 

 consult the various volumes of the Journal of the Roy. Micr. Soc, Zeitschrift fur 

 physiologische Chemie and other chemical journals ; Wormly ; Klement & Reg- 

 nard ; Carpenter ; Hogg ; Behrens Kossel mid Schiefferdecker ; Frey. 



* Most of the chemicals here named were suggested to the writer by Prof. L. M. 

 Dennis of the Chemical Department. 



