DETECTION OF ARSENIC. 121 



gas, or water impregnated with that gas ; black flux, a com- 

 pound formed by deflagrating nitre and cream of tartar; — all 

 these furnish evidence so decided in its character that when they 

 all concur, it is almost impossible that the experimenter can be 

 deceived, in concluding that he has ascertained the presence of 

 arsenic. But when having secured these precipitates, he sub- 

 jects them to his reducing tube, Hhe experimentum cruciSy he 

 finds again the characteristic appearances produced, his mind 

 cannot fail to be convinced that he has in his hand the fatal 

 agent, which has caused the death, perhaps, or severe illnes/ 

 of some unfortunate victim to carelessness or design. 



The matter to be examined may be either food, which ban 

 been poisoned, and a portion of which has been eaten, or r 

 portion of that which having been swallowed has been ejected 

 from the stomach, and is much mixed with fluids from the 

 stomach. It belongs not to this place to describe the symp- 

 toms or effects which, following the ingestion of a meal, should 

 induce suspicion of poison having been taken. When the task 

 of explaining what pertains to the duties of the chemist who 

 is called upon after well grounded suspicions have been excited, 

 has been undertaken, the examiner should first ascertain that 

 due precautions have been observed in securing the sus- 

 pected matter, especially if fluid, in a perfectly clean vessel, 

 and that no opportunity has occurred for any admixture of a 

 deleterious agent subsequent to its having been suspected, or 

 before it is given into his charge. Having obtained this 

 essential information a ready mode of deciding promptly whe- 

 ther there be any reason for proceeding to an analysis, will be 

 for the chemist to evaporate a small portion of the fluid, and 

 to throw the resulting extractive upon burning coals. Should 

 the alliaceous odour of arsenic be developed, it induces him 

 at once to proceed to the employment of his liquid re-agents, 

 and his experiments commence. If the subject of examina- 

 tion be a simple colourless fluid it is filtered, and the filter care- 

 fully washed with distilled water. The resulting clear solu- 

 tion is then distributed among as many test glasses as it is pro- 

 posed to apply tests, say three or four. To each he applies 

 re-agents, which are appropriate to indicate the presence of 

 arsenic, and if it be dissolved in the filtered solution, he finds 

 that the ammoniacal nitrate of silver gives a bright yellow 

 16 



