Experiments tn the Oxidation of Met ah hy Ele^rldty. 137 



Defcription of an apparatus in which Metallic Wires are converted into Oxides by Electric 



Difcharges. 



Fig. II, Plate VII. a h, c d is a glafs receiver, about ten inches high, and fix inches 

 diameter. To the wideft end is cemented a large round brafs plate, a l>, perfedly air tight, the 

 other end is mounted with a brafs collar, upon which a brafs cap, /ly, is fere wed, alfo perfe£lly 

 air tight. / is an air cock, one end of which is fcrewed into the middle of p q, and the 

 other into a foot on which the inftrument ftands; « are two air cocks fcrewed faft to th'e 

 broad brafs plate, with holes communicating with the infide of the receiver. Upon each of 

 thefe cocks is fcrewed a glafs tube bent, as is reprefented j their communication with the 

 infide of the receiver is opened or fhut by means of n and 0. In the infide of /> y is a wheel 

 and axis moving upon two pivots, ferving to wind up a quantity of wire in readinefs for ex- 

 ploding, m is a brafs tube about three inches long, and three quarters of an inch in 

 diameter, flopped at each end with cork, and the middle filled with hogs'-lard ; this ferves 

 to draw the wire through ready for exploding. 



The wire which is intended for ufe, muft be bound to a packthread of the fame length, 

 at different places, and at about four inches a'funder; it muft be wound upon the axis of the 

 wheel \n p q\ the tube m muft be fcrewed off from the plate, and the end of the wire muft be 

 diredled through the hole wherein m was, by means of a long brafs needle, which muft be 

 puftied through the cork and hogs'-lard, in »/, with the packthread and wire in the eye of 

 the needle ; when it is drawn through, the packthread and wire will follow, and be kept 

 air tight by the hogs'-lard and cork ; m muft be fcrewed to the plate as before, and the 

 packthread drawn through m till it is feen nearly ftraight in the infide of the receiver, as at 

 h. In this ftate, pour into the lower bend of k about half of an inch of mercury, and ia 

 the lower bend of / a little water, reprefented by the dots in each. It is evident, from 

 the conftruftion of the inftrument, that if all the fcrews be perfeftly air tight, the cocky 

 (hut, and the cocks « open, the leaft alteration that happens to the air in the infide of the 

 receiver, with refpeft either to encreafe, decreafe, denfity, or rarefaftion, will be 

 fhewn either by the mercury or water, in either one or both gages ; if confiderable, the 

 mercury will fhew it, and if too little to affeft the mercury, the water gage will Ihew it : 

 if by any procefs the temperature of the air within the receiver ftiould be raifed, it will 

 caufe the air to expand, and the mercury and water in the gages to move towards u u, but 

 if it fhould be Idwered, the mercury and water will move towards i k; fo likewife if any 

 alteration, with refpeft to temperature, happens in the furrounding air, the gages will 

 flicw ;t accordingly ; and as this is continually changing, it is neceffary that the apparatus, 

 after is prepared for the experiment, and ready for exploding of the wire, (hould be fet 

 in fome medium which is not fo changeable. For this purpofe water feems to be the moft 

 convenient ; but as it is a conduiSlor of ele£triclty, the apparatus muft not remain in when 

 the difcharge is given through it ; fo that before, and after the difcharge, it muft only 



Vol. V. — July 1801. T , be 



