Chemistry. XXXik 
The method of proceeding to analyze the ores of cobalt sug- 
gested to Laugier by the preceding facts, is the following : 
(1.) Let the ore be roasted to drive off as much of the arsenic 
as possible. | 
(2.) Dissolve the roasted ore in nitric acid and evaporate 
neatly to dryness to get rid of the arsenious acid. 
(3.) Pass a current of sulphuretted hydrogen gas through the 
liquid till the whole of the arsenic and copper (if any be present) 
be thrown down. 
(4.) Heat the liquid to drive off the excess of sulphuretted 
hydrogen, and precipitate the metals by means of carbonate of 
soda. 
(5.) Treat the carbonates with oxalic acid to separate the iron. 
Then dissolve the oxalates of cobalt and nickel in ammonia to 
separate these two metals. 
Laugier informs us that he detected nickel in the cobalt ore 
of Tunaberg, though the presence of that metal had not hitherto 
been suspected in it. 
10. Brass.—I was much amused by a remark which Mr. Gill 
has thought proper to make upon an observation of mine in my 
Historical Sketch of Chemical Science for 1817. I stated the 
well-known fact that old Dutch brass was much more valued by 
watchmakers than British brass, and gave my reasons for the 
difference between them. The Dutch brass is a compound of 
two atoms copper and one atom zinc; while English brass is a 
compound of one atom copper and one atom zinc. I think I 
generally write so perspicuously that my meaning can hardly be 
mistaken ; yet Mr. Gill insinuates, in pretty broad terms, that I 
considered the partiality of watchmakers for the Dutch brass as 
a prejudice (Annals of Philosophy, xii. 125); though I had 
stated, in as clear a manneras | could, the reason of the superio- 
rity of the Dutch over the British. The prejudice of my friend, 
the watchmaker, did not consist in considering the Dutch brass 
as better for his purpose than the English, which is really the 
case; but in supposing that the art of making that good kind of 
brass is lost. I pointed out how it might be easily manufactured 
at the pleasure of the brass maker; and Mr. Gill informs us in 
the article already quoted that his father-in-law intended to set 
up a manufactory of this old superior kind of brass. 1 am glad 
to hear it. He will prove the truth of what I ventured tv assert 
on general grounds, that modern brass makers may, if they think 
proper, make as good brass as that which the watchmakers value 
sohighly, _ 
Whatever Mr. Gill may think upon the subject, I must be 
allowed to consider my observations as of some importance. 
They were founded on experiment, and they explained a fact 
generally known, but not previously accounted for, that old 
Dutch brass is superior in ductility, &c. to English brass. 
JL. Bismuth—It was observed many years ago by Dufoy 
