POLARISED LIGHT. 



115 



been a favourite subject of inquiry with the professional man to trace 

 the course of remedies in the system of the patient under his care, and 



fc*l 



*i < 



*r 



c, 



fig. 80. Urinary Salts. 



a, Uric acid deposit. 1), Oxalate of lime, octahedral crystals of. c, Oxalate of lime 

 allowed to dry, forming a black cube, d, Oxalate of lime, as it occasionally appears, 

 termed the dumb-bell form. 



to know what has become of the various substances which he might 

 have administered during the treatment of the disease. 



Having been struck with the facility of application, and the ex- 

 treme delicacy of the reaction of polarised light, when going through the 

 series of experiments upon the sulphate of iodo-quinine, I determined 

 upon attempting to bring this method practically into use for the de- 

 tection of minute quantities of quinine in organic fluids; and after 

 more or less success by different methods of experimenting, I have 

 at length discovered a process by which it is possible ta obtain demon- 

 strative evidence of the presence of quinine, even if in quantities not 

 exceeding the 1-1 00,000th part of a grain; in fact, in quantities so 

 exceedingly minute, that all other methods would fail in recognising 

 its existence. Take for 



Test-fluid A mixture of three drachms of pure acetic acid, with 

 one fluid-drachm of rectified spirits-of-wine, to which add six drops of 

 diluted sulphuric acid. 



One drop of this test-fluid placed on a glass-slide, and the merest 

 atom of the alkaloid added, in a short time solution will take place ; then, 

 upon the tip of a very fine glass-rod let an extremely minute drop of 

 the alcoholic solution of iodine be added. The first effect is the produc- 

 tion of the yellow or cinnamon- coloured compound of iodine and quinine, 



