209 
the Arseniates of Copper , and of Iron. 
have not yet been so fortunate as to form the other combi- 
nations ; but do not doubt, that art may one day succeed in 
obtaining them. 
REMARKS. 
Before I conclude this section, which hitherto has had for 
its object a particular account of certain kinds of copper ore, as 
well as of their matrices, it may not be superfluous to offer a few 
remarks, not foreign to the present subject, upon some methods 
generally used in the docimastic art. To prove the presence of 
different substances in fossils, is an object of delicate research ; 
but, to determine proportions with accuracy is the most diffi- 
cult operation of analytic chymistry, and often eludes investi- 
gation. It is rather a pleasing reflection to think, that we 
are in the infancy of chymical exactness ; and that we may see 
the day of improvement, when the errors which we now com- 
mit will require all the aid of self-complacency to be in the 
least excused. And it may be of more real utility to state with 
frankness, although we cannot account for them, those ano- 
malous appearances which so frequently occur, than to court 
the phantom of rigid accuracy, the reality of which we can as 
yet, but in a few instances, be sure we have attained. For, 
every observation, however trivial, of this kind, will hasten the 
arrival of that moment when we shall be enabled to approach 
a little nearer to truth. 
I have, for many reasons, preferred boiling the nitrate of 
copper with either of the fixed alkalis, to the method generally 
recommended, which is, to precipitate all the copper from its 
solvent, by carbonate of potash, or of soda; then, to redissolve 
in muriatic acid ; and to precipitate, in the metallic state, by 
a plate of polished iron. 
mdccci. E e 
