in the Urine of Patients. 173 



sethereal solution evaporated to dryness by a warm water bath, 

 as before, gave '61 additional alkaloid. 



Therefore ^= + ^r = 1'4 grain of alkaloid were obtained by 



these two operations from the 8 fluid ounces of urine. 



Now to determine whether it were quinine, the following pro- 

 cess was followed : — 



Test-fluid. A mixture of 3 drachms of pure acetic acid, with 1 

 fluid drachm of rectified spirit of wine, to which 6 drops of diluted 

 sulphuric acid were added. 



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

 merest atom of the alkaloid added ; time given for solution to 

 take place ; then upon the tip of a very fine glass rod an extremely 

 minute drop of the alcoholic solution of iodine added ; the first 

 effect is the production of the yellow or cinnamon-coloured com- 

 pound 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 j after a time the acid 

 liquid again flows over the spot, and the polarizing crystals of 

 sulphate of iodo-quinine are slowly produced in beautiful rosettes. 

 This succeeds best without the aid of heat. 



To render these crystals evident, it merely remains to bring 

 the glass slide upon the field of the microscope with the selenite 

 stage and single tourmaline beneath it ; instantly the crystals 

 assume the two complementary colours of the stage ; red and 

 green supposing that the pink stage is employed, or blue and 

 yellow provided the blue selenite is made use of. All those 

 crystals at right angles to the plane of the tourmaline producing 

 that tint which an analysing plate of tourmaline would produce 

 when at right angles to the polarizing plate ; whilst those at 90° 

 to these educe the complementary tint, as the analysing plate 

 would also have done if revolved through an arc of 90°. Vide 

 Plate II. figs. 1 and 2. 



This test is so ready of application and so delicate, that it 

 must become the test, par excellence, for quinine. Vide figs. 1 

 and 2. 



Not only do these peculiar crystals act in the way just related, 

 but they may be easily proved to possess the whole of the optical 

 properties of that remarkable salt of quinine, so fully described 

 by me in the Philosophical Magazine for March 1852, and the 

 chemical analysis of which was published in the number for 

 September of the same year ; in fact, these crystals are perfectly 

 identical with the sulphate of iodo-quinine in every respect. 



To test for quinidine, it is merely necessary to allow the drop 

 of acid solution to evaporate to dryness upon the slide, and to 

 examine the crystalline mass by two tourmalines, crossed at 



