10 Dr. Guy, on Microscopic Sublimates. 



The second — a solution of carbazotic acid (^4^0) — puts on^ 

 when dry, the appearances shown in fig. 11. 



I take this opportunity of submitting photographs of one 

 other test — the nitro-prusside of sodium, which not only yields 

 a very beautiful arborescent crystal^ but appears to be' 

 somewhat modified and improved by more than one of the 

 alkaloids (see fig. 12). 



The effect of the bichromate of potash is sometimes instan- 

 taneouS;, often speedy, occasionally slow. It varies, probably, 

 with the thickness and character of the crust, and is influ- 

 enced by other caiises difficult to determine. When instan- 

 taneous, the crust is dissolved, and the whole field is 

 sprinkled over with groups of fine prisms, radiating from a 

 point and projecting into the field; when more slowly 

 formed, the field is strewn with thin plates of various forms, 

 among which the square plate is most common. When the 

 process goes on still more slowly (and this seems to happen 

 most frequently with the thicker crusts) groups of larger 

 plates, square and oblong, triangular and irregular, spring 

 up in blank spaces of the crust formed by its partial destruc- 

 tion. The colour of these crystals, in all their forms, is a 

 lemon-yellow by transmitted, and a rich golden by reflected, 

 light. The dry crust shows one or more of these forms 

 blended with the arborescent crystals of the reagent. This 

 reaction is, I believe, quite characteristic. (See PI. II, fig. 16, 

 from which all crystals of the reagent are omitted.) 



The effect of the carbazotic acid is equally characteristic, 

 and much more uniform in its occurrence, and constitutes a 

 test for strychnine, upon which, I believe, that the utmost 

 reliance may be placed. Helwig, who describes the reac- 

 tions of this test with solutions of the salts of strychine, but 

 not as a test for its sublimates (for he only describes the re- 

 actions with the sublimates of distilled water, liquor ammo- 

 nise, dilute hydrochloric acid, and dilute chromic acid) — 

 Helwig describes this acid as among the most delicate tests 

 for strychnine, and says that a solution containing one part 

 in 20,000 will develope sharply- defined crystals. Dr. Letheby 

 also, in his papers published in the ' Lancet,^ in the months 

 of June and July, 1856, figures the crystals formed by car- 

 bazotic acid and the acetate of strychnine, as seen in the dry 

 spot. Helwig, following the entire reaction as it takes place 

 under the microscope, describes the formation of delicate, 

 greenish-yellow " millfoil-leaves," and, at the close of the 

 reaction (in the dry spot), large colourless plates, which are, 

 doubtless, the crystals proper to the reagent. But he does 

 not notice that Avhich foi'ms the leading feature of four 



