CH. VII.] MICRO-CHEMISTRY. 181 



in a tall glass vessel to deposit its sediment. Take a concentrated drop of this sed- 

 iment and mount it on a slide under a cover-glass. Study the preparation with the 

 microscope. Probably there will be an abundance of animal and vegetable life as 

 well as of solid sediment. Put a drop of dilute sulphuric acid (Acidum sulphuri- 

 cum, i. e., strong sulphuric acid i gram, water 9 grams) at the edge of the cover 



Fig. 139. CzapskVs Ocular Iris-diaphragm with cross hairs 

 for examining and accurately determining the axial images of 

 small crystals. The iris diaphragm enables the observer to 

 make the field as large or small as desired. 



A. Longitudinal section. 



B. Transection, showing the cross lines and the iris dia- 

 phragm with the projecting part at the left, by which the dia- 

 phragm is opened and closed. (Zeiss' Catalog, No. so). 



and at the opposite edge a small piece of the lens paper (Fig. 128). The acid will 

 gradually diffuse, and if the solid particles are carbonate of lime, minute bubbles 

 will be seen to be given off. If they are silica or clay no change will result. Sul- 

 phuric acid is recommended for this, as the microscope would be far less liable to 

 injury than as if some acid giving off fumes were used. 



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

 a so-called test fluid 12 cc. of glacial acetic acid, 4 cc. of 95% alcohol, and 7 drops 

 of dilute sulphuric acid (§ 319) 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 ex- 

 tremely minute drop of au alcoholic solution of iodine. "The first effect 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-quiuine are slow- 

 ly produced 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 further papers on micro-chemistry by Dr. Hera- 

 path, see the Royal Society's Catalog of Scientific Papers. 



\ 321. List of Substances for the Study of Crystallography with the Microscope.* 

 The substances are crystalized on the cover-glass in all cases, and in all cases, ex- 

 cept where otherwise stated, a saturated aqueous solution of the substances was 

 first prepared. 



1. Ammonium chlorid ; 2. Ammonium copper chlorid ; 3. Barium chlorid ; 

 4. Cobalt chlorid (beautiful crystals obtained by mixing the saturated aqueous so- 

 lution with an equal volume of 95% alcohol). Crystallization in a current of dry 



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

 Dennis, of the Chemical Department. 



