PRESENCE OF ARSENIC. 607 
caused the crust, if of. arsenic, to be volatilized 
from that part of the slip of glass on which it was 
deposited, small crystals are to be observed ad- 
hering to that part of the slip and of the interior 
of the tube, which was not immersed in the hot 
oil, chiefly to that part which was from } to $ an 
inch above the surface of the oil. It will be per- 
ceived, too, that I do not lose the chance of try- 
ing the action of the other usual tests, but that I 
have an opportunity of testing in a two-fold man- 
ner the character of any crust in question: having 
cut off with a file one end of the tube, the metal 
or its oxide can be operated upon with nitric acid 
and the ammoniacal nitrate of silver, or with such 
other tests as we may choose to apply. 
The greatest objection against my mode of 
operating is the tediousness attending the having 
to wait so long for the conclusion of an experi- 
ment, and the great care required in watching the 
range of the thermometer ; but, I hope, this may 
be alleviated by substituting for oil as the heating 
medium, some other liquid whose boiling point is 
stable within the range of the temperature re- 
quired: probably a satwrated solution of some 
salt may answer, but, at present, I am not aware 
of any that will. 
