196 Miscellanies. 



it in an account of an examination, of another arsenical compound, 

 which has been the subject of many experiments. It is the arseni- 

 uret of iron with sulphuret of cobalt, described by Prof. Dana^ and 

 which you noticed in your late work.* I was engaged in the exam- 

 ination, so long ago, as when its containing cobalt was the subject of 

 your correspondence with him, and it has been occasionally the sub- 

 ject of experiment since. It is a refractory compound, and while a 

 pupil with Prof. D. I subjected it to all the processes which had been 

 published, with a determination to finish its examination. Finding 

 the characters of the constituent metals erroneously described, a 

 partial examination of them became necessary ; want of sufficient 

 leisure afterwards, prevented my completing what was begun. Some 

 months since I prevented a friend from publishing his opinion, that it 

 contained no cobalt, by actual experiment. Prof. D. was however 

 led into an error, in relation to the quantity of cobalt which can be 

 detected by the blowpipe, from his trusting to the purity of a speci- 

 men from Frederick Accum ; it was merely a fused ore of cobalt : 

 a ten thousandth of cobalt, can be detected by a practised eye. 



The value of the blowpipe as an instrument of research, has not 

 been duly appreciated in this country ; few I believe use it with skill, 

 even in mineralogical inquiries. 



9. Manufacture of lead pots, &i-c. by Messrs. Dixon. — We have 

 pleasure in stating to the public, that there has lately been establish- 

 ed in Salem, Massachusetts, a Manufactory of black lead pots, by a 

 process, the discovery of Messrs. J. and F. Dixon. These pots, as 

 we learn from the artists who have used them, prove on trial to pos- 

 sess great advantages over other pots. 1st. They resist sudden change 

 of temperature better. 2d. They are not liable to change their 

 form, on pressure of the tongs in a great heat. 3d. They are found 

 to be far more durable. But their high estimation with those who 

 have used them, is, perhaps, best proved by the fact, that the orders 

 for them, have been so frequent, that the manufacturers have not been, 

 and are not now able to make them so flist as they are called for. 



****** •JS- 



We are informed also that one of the Messrs. Dixon has ground 

 and polished a concave lens for the venerable and ingenious Dr. B. 

 Lynde Oliver, of Salem, who has been constructing an achromatic 



■" Elemoijts of Chemistry, Vol II, p. 200. 



