120 DETECTION OF ARSENIC. 



scribed. Counsel in one of our courts, have been known 

 during a trial for poisoning, to apply the Scripture expression 

 of 'seek and ye shall find,' to the chemists who were examined 

 on the trial. Thus much in extenuation of the caution which 

 has been given, to come to the examination totally unbiased. 

 The pieces of apparatus required for such an analysis, are few 

 and simple in their construction: they consist of a spirit lamp, 

 test tubes, a funnel, two or three reducing tubes, a pair of small 

 copper plates, and a small galvanic arrangement invented by 

 Mr. Fischer of Breslaw. With this appareil and the necessary 

 tests, which will be hereafter mentioned, the experimenter is 

 provided with all the means necessary to a full examination of 

 the suspected matter. His process is founded on the follow- 

 ing facts : That certain reagents which he employs are known 

 to produce precipitates of a particular colour and density with 

 the salts of arsenious and arsenic acid: that the salts of these 

 acids, when exposed in a reducing tube, with the black flux, 

 (consisting of carbon and an alkaline salt,) are decomposed, the 

 acid of the arsenic being reduced, and the metal sublimed in 

 the upper portion of the tube, under a particular aspect; that 

 compounds, containing arsenic, mixed with black flux, when 

 heated between two copper plates, are decomposed, the metal 

 being reduced and combining with the upper plate, forming 

 an alloy of silvery whiteness ; and finally, that when a solu- 

 tion containing a salt of arsenic is brought into contact with 

 the poles of a galvanic battery, the salt is decomposed, the 

 metal being reduced and found alloyed with the negative pole 

 if it be susceptible of such a combination, or else simply coat- 

 ing it. There is also another property peculiarly character- 

 istic of arsenic, which is the odour exhaled, when arsenic, or 

 any one of its compounds, is thrown upon burning coals. This 

 odour has been compared to that of garlic, or phosphorus, and 

 is generally described in the books, as alliaceous. It is so 

 strongly marked, that when once smelled, it is scarcely possi- 

 ble to forget it. 



Having thus explained the principles upon which the ope- 

 rations about to be described are based, I proceed to specify 

 the tests which are usually applied in the analysis of a fluid 

 supposed to contain arsenic. They are ammoniacal sulphate 

 of copper ; ammoniacal nitrate of silver ; sulphuretted hydrogen 



