204 M. Becquerel on the Devdopnent 



precipitated to the bottom, I pour off and add fresh water, 

 permitting the powder to subside each time before the water 

 is poured off, so as to free the substance as much as possible 

 from the acid ; and then I pour it on a piece of fikering paper, 

 and place the powder in an airy room to dry. It should be kept 

 in a corked (not stopper) bottle. Sometimes the powder is 

 quite white, and often light brown, in colour ; but this is of no 

 consequence. To fill the caps, I use a small ivory pin, scooped 

 at one end to take up the powder, and flat at the other end to 

 fit the bottom of the cap : I place a very small portion of the 

 powder in the cap, just sufficient to cover the bottom, and 

 then dip the flat end of the pin in a strong tincture of gum 

 benzoin, so as only to moisten it, (if I may be allowed the ex- 

 pression, ) and press the pin so moistened on the powder in the 

 cap, and gently turn it, so as to secure the powder in the cap, 

 the tincture acting as a varnish on the surface of the powder. 

 After a little practice, a great number of caps may be pre- 

 pared in a short time in this manner ; and I have no doubt the 

 fulminating mercury will be preferred, on trial, to the percus- 

 sion powder at present used. Several of my sporting friends 

 have tried some caps I gave them charged with the fulmi- 

 nating mercury, and all agree as to its superiority to the com- 

 mon preparation from chlorine of potass. 

 I am, gentlemen, 



Your very obliged servant, 

 Hereford, Sept. 18, 1823. E. G. Wright. 



P.S. The fulminating meixury ought to be made in an out- 

 house, or in an unfurnished room, under a chimney, on account 

 of the nitrous fumes extricated in the first, and the nitrous 

 ether in the second part of the process. It may be made 

 into a paste with weak tinctureof gum benzoin, and granulated, 

 for the magazine locks of Forsyth and other makers, but must 

 not be mixed with any other substance. 



XLII. Expei-iments 07i the Development of Electricity by 

 Pressure ,■ — Laivs of this Development. By M. Becquerel, 

 Ancien Chef de Bataillon du Genie *. 



Stateme?it qf the Phccnomena. 

 /COULOMB, in a series of researches respecting the de- 

 ^^ velopment of electricity by friction, was led to conjecture 

 that the dilatation and compression experienced by the particles 

 of the surfaces of bodies had a determinative influence upon 

 the nature of the electricity developed by each of them. M. 



* From the Annates dc Chimie el de Phhique, torn, xxif, p. 5. 



Biot, 



