8 Dr. Guy, on Microscopic Sublimates. 



had been told that it was one of a poisonous character, and 

 probably strychnine, the presumption in favour of that par- 

 ticular poison would have been greatly increased. Let me 

 mention some of the poisons which the results of the process 

 would have excluded. 



Arsenious acid would have been shut out ; for that poison 

 is wholly sublimed, without change of colour or residue, the 

 sublimate consisting of brilliant octohedral crystals ; and 

 corrosive sublimate, for it also is sublimed without change of 

 colour and without residue, and yields a sublimate not to be 

 confounded with any sublimate of the alkaloids. The active 

 principle of the blistering fly, cantharadine, too, would have 

 been excluded ; for it sublimes without residue or previous 

 change of colour. Then, among the alkaloids themselves, 

 solanine would have been excluded by the form of its 

 sublimate, which is very characteristic; and veratrine, 

 of which the sublimate assumes the form of detached 

 crystals. Then, the very peculiar development of the milk- 

 white spots in the thin mist will probably be found to occur 

 only in the case of strj^chnine, morphine, and of one or two 

 other alkaloids at the outside. 



But happily we are able to convert this likelihood into 

 absolute certainty, by treating the sublimate with appropriate 

 reagents. We owe this good fortune to a circumstance which 

 was hardly to be expected, that, in spite of change of colour, 

 melting, and deposit of carbon, the vapour given off by 

 strychnine holds the alkaloid itself in suspension; as is 

 proved by the occurrence in many sublimates of detached 

 crystals, such as we meet with in deposits from solutions of 

 strychnine, as well as by the close resemblance of the re- 

 actions of the sublimate to those of the commercial alkaloid 

 and its solutions, and the solutions of its salts. 



Among these reactions there is one of great delicacy and 

 beauty, known as the colour test. When a drop of strong 

 sulphuric acid is added to a particle of pure strychnine it 

 dissolves it without change of colour ; but if we bring 

 this acid solution in contact with a minute particle of 

 peroxide of manganese, peroxide of lead, bichromate of 

 potash, ferridcyanide of potassium, or permanganate of 

 potash, a rich blue, passing quickly into other colours, is 

 produced, and stamps the substance as strychnine. Now, this 

 reaction takes place with the sublimates of strychnine, and, 

 as I have good reason to believe, more certainly than with 

 the alkaloid in any other form. It succeeded, for instance, 

 in two sublimates containing each the T;-;^-^th of a grain, when 

 it failed Avith two deposits from a solution in ether containini^ 



