Means of detecting Arsenic in the Animal Bodi/, 6^c. 283 



ing ordinary zinc of the necessary purity to be used in Marsh's 

 apparatus. 



Sulphuric acid may contain arsenic, when manufactured with 

 sulphur obtained from pyrites holding that substance in combina- 

 tion ; but a simple distillation will serve to rid it of this impurity. 



After placing the zinc, sulphuric acid and water in the appa- 

 ratus, replace the cork with the glass tube inserted in it, and 

 when the hydrogen has been allowed to generate a sufficient 

 length of time to expel the air, inflame it as it issues from the 

 extremity of the tube ; if a porcelain plate be now applied to 

 about the middle of the flame, and no tache or spot be obtained, 

 we have the best evidence of the purity of our materials. 



Another apparent objection to the apparatus, is, that the intro- 

 duction of animal matter, either solid or liquid, causes the for- 

 mation of a large quantity of froth, which arrests the progress 

 of the operation. This, however, is so easily remedied, that it 

 need hardly be considered an objection. If the froth be not 

 in too great quantity, it will suffice to introduce a little oil, 

 which will serve to arrest its formation. Another method is to 

 turn the liquid out of the phial into a funnel, with the finger 

 placed upon the lower extremity, the froth will at once rise to 

 the surface, and by taking away the finger the liquid will pass 

 out perfectly free from it. Again, if care be taken to carbonize 

 the matter before using it, this obstacle will be removed. There 

 is still another means, and I find it to succeed very well in most 

 instances ; it is to pour the sulphuric acid destined for the for- 

 mation of the hydrogen first upon the animal matter, and then 

 pour the two upon the zinc and water ; it would appear that a 

 partial carbonization takes place. No doubt most persons will 

 now perceive that this objection possesses no weight, and vanishes 

 altogether before the means proposed to encounter it. 



The next part of this question to be examined, is, what sub- 

 stances besides arsenic produce taches with this apparatus, and is 

 there no danger of confounding them with that of arsenic? 

 They are antimony, sulphur, phosphorus and iron. Before 

 speaking of their distinguishing characteristics, it would be as 

 well to say a few words concerning that produced from arsenic. 



The arsenical tache is highly metallic, of a steel color, with a 

 shght reddish tinge, and borders of a dark rusty color ; but to 

 have a proper idea of its appearance, as well as that of the others, 



