316 Proceedings of the Royal Irish Academy. 



— to eTaporate it to dryness, and ascertain the -weight of the residue 

 or of the salt that had been dissolved in the given amount of water ; 

 and in order to obtain a saturated solution of the salt at the ordinary 

 temperature (which in some cases, ovring to the very slight solubility 

 of the salt in cold water, would not be easily effected), the usual mode 

 I adopted was to dissolve the salt in hot, or in boiKng water, and to leave 

 it to cool and stand for about twenty-four hours, so that the excess of 

 salt dissolved by heat might re-crystallize out of the solution, which, 

 after filtration to separate the crystals, the necessary quantity of it 

 was taken, evaporated to dryness, and the weight of the residue deter- 

 mined. 



I shall now proceed to describe the characters of the nitroprussides 

 of some of the more important alkaloids. I shall commence with 

 those which, owing to their sparing solubility in water, may be pre- 

 pared by precipitation. 



Strychnine Nitroprusside. 



The first I shall speak of is the strychnine salt, as this is the ^' only 

 organic nitroprusside, as far as I was able to ascertain, which has 

 received some very slight attention, and concerning which some con- 

 flicting statements have appeared. I believe that !Mr. John Horsley, 

 of Cheltenham, was the first to point out that sodium nitroprusside 

 formed a crystalline precipitate with strychnine salts, and finding that 

 where it had been added to a mixture of that alkaloid and strong sul- 

 phuric acid, the characteristic purple reaction (which is developed by 

 strychnine, when it is acted on by different oxidizing agents imder 

 those circumstances) was produced, he proposed it, the sodium nitro- 

 prusside, as a more delicate reagent than potassium bichromate for 

 that purpose. But it was subsequently shown by Rogers and !N"eu- 

 bauer that this reaction which Horsley observed was due to the nitro- 

 prusside he employed containing potassium ferricyanide, known in 

 commerce as the red prussiate of potash — a salt which, several years 

 ago, I myself proposed to be used in conjunction with strong sulphuric 

 acid, as a test for strychnine ; and which, according to my experi- 

 ments, possesses some advantages for that pui'pose over the potassium 

 bichromate, the salt which is usually employed in the detection of 

 that alkaloid. And I mention this circumstance, as in several chemical 

 works where my name has been quoted in connexion with this test, an 

 error has been made in putting the f erro- instead of the ferricyanide of 

 potassium, as the salt to be employed ; for the former, which is well 

 known under the name of the yellow prussiate of potash, has no 



* Since my investigations -vrere made, I have ascertained that Mr. Horsley, 

 several j-ears ago, proposed sodium nitroprusside as a test for certain alkaloids, and 

 pointed out that when it was added to solutions of brucine, and to those of morphine, 

 and the mixtures examined under the microscope, that characteristic crystals were 

 produced, as well as in the case of strychnine, to which he had previously directed 

 attention. See The Chemical News, vol. v. p. 355. 



