1819.] and a new Galvanic Instrument. 183 



ing on zinc, enough red lead to prevent effervescence, the 

 temperature rose from 70 to 110 Fahr. 



The power of the calorimotor is much increased by having the 

 communication between the different sheets formed by very 

 large strips or masses of metal. Observing this, I rendered the 

 sheets of copper shorter by half an inch for a distance of four 

 inches of their edges, where the communication was to be made 

 between the zinc sheets ; and, vice versa, the zinc was made in 

 the same way shorter than the copper sheets where these were 

 to communicate with each other. The edges of the shortened 

 sheets being defended by strips of wood, tin was cast on the 

 intermediate protruding edges of the longer ones, so as to 

 embrace a portion of each equal to about one quarter of an inch 

 by four inches. On one side, the tin was made to run completely 

 across, connecting at the same time 10 copper and 10 zinc 

 sheets. On the other side, there was an interstice of above a 

 quarter of an inch left between the stratum of tin embracing the 

 copper and that embracing the zinc plates. On each of the 

 approaching terminations of the connecting tin strata was 

 soldered a kind of forceps, formed of a bent piece of sheet brass, 

 furnished with a screw for pressing the jaws together. The 

 distance between the different forceps was about two inches. 

 The advantage of a very close contact was made very evident by 

 the action of the screws; the relaxation or increase of pressure on 

 the connecting wire by turning them being productive, of a 

 correspondent change in the intensity of ignition. 



It now remains to state, that by means of iron ignited in this 

 apparatus, a fixed alkali may be decomposed extemporaneously. 

 If a connecting iron wire, while in combustion, be touched by 

 the hydrate of potash, the evolution of potassium is demonstrated 

 by a rose-coloured flame. The alkali may be applied to the wire 

 in small pieces in a flat hook of sheet iron. But the best mode 

 of application is by means of a tray made by doubling a slip of 

 sheet iron at the ends, and leaving a receptacle in the centre, in 

 which the potash may be placed covered with filings. This tray 

 being substituted for the connecting wire, as soon as the immer- 

 sion of the apparatus causes the metal to burn, the rose-coloured 

 flame appears ; and if the residuum left in the sheet iron be 

 afterwards thrown into water, an effervescence sometimes 

 ensues. 



I have ascertained that an iron heated to combustion by a 

 blacksmith's forge fire will cause the decomposition of the 

 hydrate of potash. 



The dimensions of the calorimotor may be much reduced 

 without proportionably diminishing the effect. I have one ol 

 (in plates within a cubic foot, which burns off No. 16, iron wire. 

 A good workman could get 120 plates of a foot square within a 

 hollow cube of a size no larger. But the inflammation of the 



