30 



upon iron from its solution of the same red colour, except- 

 ing Copper." I have cited these examples for the purpose 

 of shewing, that a few out of the many known properties of 

 a body, may he sufficient to enable the Toxicologist to dis- 

 tinguish certain substances from all others, with which 

 science has up to this time made us acquainted. It is not 

 for a moment, however, maintained, that the medico-legal 

 analyst is, of necessity, to be limited to these few properties, 

 supposing always, that he has plenty of the substance to 

 operate upon, but it is of much importance to know that 

 where the quantity of material at his disposal is very 

 small, the evidence derived from a few of its properties 

 is sufficient to establish a certain distinction between it and 

 all other known bodies. 



T shall now proceed to describe some of the methods 

 formerly employed for demonstrating the presence of white 

 arsenic, or arsenious acid. The older analysts were far 

 behind the present day in detecting small quantities of this 

 poison. Thus Hahnemann recommended so rude an in- 

 strument as a retort, and stated, that the smallest quantity 

 he could detect was 10 grs. I shall have occasion pre- 

 sently, to shew that 7^ part of that quantity can be 

 certainly detected. Dr. Black was thought to have 

 accomplished much, when he succeeded in detecting one 

 grain of the substance in question. 



Somewhere about 70 years ago, the garlicky odour 

 evolved from subliming arsenic was almost exclusively relied 

 upon, and from a case related by Professor Metzer, occur- 

 ring about the latter end of the last century, it would ap- 

 pear, that the presence of arsenic was considered to be 

 proved, by the odour evolved by burning the dried resi- 

 duum of the contents of the stomach. 



The Tombac, or silvery alloy test, was subsequently 

 recommended. The substance suspected to contain arsenic, 

 was mixed with some carbonaceous matter placed between 



