[ 241 ] 



XLIV. Description of the apparatus invented ly W. H. 

 Pepys, Esq., for the Decomposition of the Alkalis under 

 Naphtha, by Galvanism. 



1 HE celebrated discovery of the compound nature of the 

 alkalis hy professor Davy excited the attention of all classes 

 of philosophers. Numerous experiments and apparatus for 

 the more easily and permanently securing these volatile and 

 decomposable metals were invented. — Of the several appa- 

 ratus for decomposing the alkalis under naphtha, the most 

 simple is that invented by Mr. Pepys. 



Mr. Knight, of Foster-lane, who has made several, fa- 

 voured us with the instrument from which the present Plate 

 is taken : 



C. A cylinder of glass with a pedestal ground glass stop- 

 per P, perforated through to allow a communication to take 

 place, by means of a wire, between two metallic plates 

 cemented to the top and bottom of the stopper. The 

 lower plate is of copper : the upper of platina. 



W. A wooden cover, through which a platina wire 

 (with a plate of the same metal riveted to the inferior end) 

 is allowed to slide. 



Use. — Tlie copper base of the pedestal is brought in con- 

 tact with the positive end of the trough : the potash, slightly 

 moistened, is laid on the platina plate p. The cylinder is 

 then filled with naphtha, the wooden cover put on, and the 

 platina wire N, previously communicating with the neo^a- 

 tive end of the trough, is suffered to come into contact with 

 the potash or soda. Decomposition is immediately eflected. 

 Part of the metal sometin}es floats, but the larger portion 

 will be found imbedded in the alkali. A considerable por- 

 tion of gas is evolved from the decomposition of both the 

 naphtha and the alkali. 



By a simple motlification of the above apparatus, we un- 

 derstand Mr. Pepys has collected the whole of the gases 

 during decomposition. 



V(,l. -^i.No. 124. 5f'/>^ 1808. Q XLY. On 



