36 Tests for detecting the Presence of Arsenic, [Jan. 



glass tube, when cold, may be separated from its sealed end by 

 the action of a file, which will enable us to collect and examine 

 the metallic sublimate. If a portion of this brilliant matter be 

 laid on heated iron, it will indicate its nature by exhaling in 

 dense fumes, having a powerful smell of garlic. Another por- 

 tion should be reserved for future experiments. 



" This method of detecting the presence of arsenious acid has 

 been considered the most decisive, and indeed the only unex- 

 ceptionable one, but of this we shall speak hereafter ; at present 

 we have only to observe, that it is very far from being a minute 

 test ; for Dr. Bostock confesses that where less than three- 

 fourths of a grain were used, he could not say that the metallic 

 crust was clearly perceptible ; and Dr. Black appears to have 

 considered that one grain was the smallest quantity which could 

 be distinctly recognised by such a process." 



This method is unquestionably excellent, but I have found 

 that the metallization may be very conveniently effected by 

 means of a spirit-lamp. Indeed it may possibly happen that a 

 glass tube, such as is requisite for the above process, cannot 

 be procured at the moment in which it may be wanted ; a 

 spirit-lamp may also be wanting. I have adopted the fol- 

 lowing plan : let a piece of tin plate, about an inch long, be 

 coiled up into a cylinder of about 3-8ths of an inch in diameter, 

 and if the edges be well hammered, it is not necessary to use 

 solder. Perforate a cork previously fitted to a vial, and put a 

 cotton wick through the short tin tube, and the tube through 

 the cork, the lamp is now complete, and will afford a strong 

 flame, taking care of course not to prevent the rise of the spirit 

 by fitting the cork too closely. Instead of a test tube about six 

 inches in length, which however is certainly much to be prefer- 

 red, I have employed, with the precautions copied from Dr. 

 Paris, a common draught vial ; those best adapted for the pur- 

 pose are called ten drachm vials, for they are long in proportion 

 to their diameter. In using these vials, the suspected powder 

 and black flux must not reach the bottom of the vial, for, on 

 account of its thickness, it will readily break on the application 

 of heat. The vial, therefore, must be heated laterally, the 

 arsenic will readily sublime, and will, after the vial has been 

 divided by a file, if heated in the spirit-lamp, give out the well- 

 known alliaceous smell. Indeed if the quantity of arsenious 

 acid be large, the smell which the volatilized metal affords may 

 be resorted to in confirmation of other evidence ; but it is to be 

 observed, that it must be mixed with charcoal, or some sub- 

 stance which reduces it to the metallic state, for arsenious acid, 

 though volatilized by heat, and exhibiting white fumes, does not 

 give any smell. 



I have now concluded the sketch which I proposed giving, 

 and, if I mistake not, the use of animal charcoal in the mode 

 described, will afford some facilities. I hope also that I have, 

 in some degree, strengthened the evidence which is afforded by 



