VOL. LVI.] PHILOSOPHKAL TRANSACTIONS. 307 



of salt, with some fine copper wire in it. Tlie wire seemed not at all acted on by 

 the acid, while cold ; but with the assistance of a heat almost sufficient to make 

 the acid boil, it made a considerable effervescence, and the air passed through the 

 bent tube, into the bottle d, pretty fast, till the air forced into it by this means 

 seemed almost equal to the empty space in the bent tube and the bottle a : 

 when, on a sudden, without any sensible alteration of the heat, the water rushed 

 violently through the bent tube into the bottle a, and filled it almost entirely full. 

 The experiment was repeated again in the same manner, except that I took 

 away the bottle d, and let out some of the water of the cistern : so that the end 

 of the bent tube was out of water. As soon as the effervescence began, the 

 vapours issued visibly out of the bent tube ; but they were not at all inflam- 

 mable, as appeared by applying a piece of lighted paper to the end of the tube. 

 A small empty phial was then inverted over the end of the bent tube, so that the 

 mouth of the phial was immersed in the water, the end of the tube being within 

 the body of the phial and out of water. The common air was bv degrees ex- 

 pelled out of the phial, and its room occupied by the vapours ; after which, hav- 

 ing chanced to shake the inverted phial a little, the water suddenly rushed in 

 and filled it almost full ; thence it passed through the bent tube into the bottle a, 

 and filled it quite full. Hence it appears likely that copper, by solution in the 

 marine acid, produces an elastic fluid, which retains its elasticity as long as there 

 is a barrier of common air between it and the water, but which immediately 

 loses its elasticity, as soon as it comes in contact with the water. In the first 

 experiment, as long as any considerable quantity of common air was left in the 

 bottle containing the copper and acid, the vapours, which passed through the 

 bent tube, must have contained a good deal of common air. As soon therefore 

 as any part of these vapours came to the farther end of the bent tube, where 

 they were in contact with the water, that part of them, which consisted of the 

 air from copper, would be immediately condensed, leaving the common air un- 

 changed ; by which the end of the tube would be filled with common air only ; 

 by which means the vapours, contained in the rest of the tube and bottle a, 

 seem to have been defended from the action of the water. But when almost all 

 the common air was driven out of the bottle, then the proportion of common 

 air contained in the vapours, which passed through the tube, seems to have been 

 too small to defend them from the action of the water. In the 2d experiment, 

 the narrow space left between the neck of the inverted phial and the tube would 

 answer much the same end, in defending the vapours within the inverted phial 

 from the action of the water, as the bent tube in the first experiment did in de- 

 fending the vapours within the bottle from the action of the water. 

 Pakt II. — Containing Experiments on Fixed Air, or that Species of Factitious 



R K 2 



