of the Galvanic Deflagrator, Sj-c. 243 



zinc plates are exposed only on one side. The sum of the 

 surfaces on which the acid can act is therefore the same as in 

 a deflagrator of .50 pairs, in which each zinc plate is assailable 

 on both sides. It ought to be understood, that the box con- 

 taining the 100 Cruickshank plates is open at bottom, and is 

 of such dimensions as to occupy the place of a box, contain- 

 ing 50 pairs of the deflagrator, receiving the acid in its inter- 

 stices from below, in the same manner, by a partial revolution 

 of the trough, fig. 4. 



Fig. 6. represents a box, containing 200 Cruickshank plates. 

 This differs from the common Cruickshank trough only in hav- 

 ing the interstices as narrow as those between the copper and 

 zinc surfaces of the deflagrator pairs represented by fig. 2 ; and 

 in the mode in which the acid is thrown off or on the whole 

 series, which does not differ materially from that described in 

 the instance of fig. 1. 



On contrasting the series of 50 (fig. 4) with Cruickshank's 

 plates in the box (fig. 5) the deflagrating power of the latter 

 was found comparatively feeble; and even when compared 

 with the Cruickshank trough (fig. 6) in igniting metals or car- 

 bon, the 50 pairs (fig. 4) were found greatly superior. The 

 shock from the Cruickshank trough was more severe. You 

 must recollect, that in former experiments I found that galvanic 

 plates, with their edges exposed as they are in the porcelain 

 troughs used by Sir Humphry Davy, were almost inefficient 

 when used without insulation, as are the pairs of the defla- 

 grator. This demonstrates that an unaccountable difference 

 is producible in the galvanic apparatus by changes of form or 

 position. 



Being accustomed to associate the idea of the zinc pole, in 

 a Voltaic series, with the end terminated by zinc, and the 

 copper pole, with the end terminated by copper, I was sur- 

 prised to find that, in decomposing water, the oxygen was at- 

 tracted by the wire connected with the copper end of my de- 

 flagrator, while the hydrogen went to the wire connected with 

 the zinc end. Subsequently, however, it occurred to me, that 

 in the deflagrator the zinc pole is terminated by copper, the 

 copper pole by zinc ; and hence the apparent anomaly, that 

 oxygen appears to be attracted by copper, anil hydrogen to 

 be attracted by zinc. 



The projection from the carbon, exposed between the poles, 

 takes place at the negative pole of the pile, and not at the posi- 

 tive pole, as you have alleged; and thus your observation, 

 that the current of igneous matter is from the copper to the 

 zinc, may be reconciled with the Franklinian theory. 



The observations which are the subject of this comniunica- 

 H h 2 tion, 



