542 Mr. W. Weston on the Application of 



and we have 



\ir— arctan\/# = 2 (arc tan q — arc tan q 3 -f arc tan q b — &c); 

 while if we put >/<? for q } since 



arc tan _^ . = 2 arc tan ^A:, 

 1 — a; 



we have 



arctan\/I=2 (arc tan v^ — arc tan ^/# 3 -fare tan^/*? 5 — &c), 

 both of which are deserving of notice. 



The former of these two formulae may also be written 

 am|K — J-7r = 2(arctan q— arc tan# 3 -f arc tan q 5 — -&c). 



LXIII. 7%c Application of Phosphorus to the " Poling " of Cop- 

 per. By William Weston, Esq., Associate of the Royal 

 School of Mines, and Chemist at H. M. Dockyard, Ports- 

 mouth. 



To William Francis, Esq., Ph.D. 



Royal School of Mines, 

 My DEAR Francis, Jermyn Street, Nov. 17, 18/5. 



THAVE much pleasure in communicating to you for publi- 

 cation in the Philosophical Magazine the following account 

 by Mr. William Weston, of the use of phosphorus in poling 

 copper. The process, which originated with Mr. Weston, is 

 novel, and, it seems to me, of much practical importance. A 

 few months ago I visited Chatham, where it has been in opera- 

 tion for a year or two, in order to inquire concerning it, and the 

 information which I obtained was highly satisfactory. 



I remain 



Very truly yours, 

 William Francis, Esq. John Percy. 



The use of phosphorus in that part of the operation of refining 

 copper known as the poling process, which has been now for 

 some time carried out in the Government metal-mills at Chat- 

 ham Dockyard, is attended with such a marked effect on the 

 metal as to render a short notice of it desirable, ' both on the 

 ground of its scientific interest and probable practical importance. 



The primary object of the addition of phosphorus at Chatham 

 is to increase the density of the copper, with the expectation that 

 the sheathing made from it for the navy would be thereby rendered 

 more durable. Such increased density must greatly improve 

 copper for many subsequent processes of manufacture ; but, in 



