Sir H. Davy on the Phenomena of Volcanoes. 87 



down. Where it issued from the mountain, it was nearly white 

 hot, and exhibited an appearance similar to that which is shown 

 when a pole of wood is introduced into the melted copper of 

 a foundry, its surface appearing in violent agitation, large bub- 

 bles rising, which in bursting produced a white smoke ; but 

 the lava became of a red colour, though still visible in the sun- 

 shine, where it issued from under the bridge. The force with 

 which it flowed was so great, that the strength of the guide, a 

 very stout young man, was insufficient to keep a long iron rod 

 in the current. The whole of its course, with two or three 

 interruptions where it flowed under a cooled surface, was 

 nearly three quarters of a mile, and it threw off clouds of a 

 white smoke. It smoked less as it cooled and became pasty ; 

 but even where it terminated in moving masses of scoria, smoke 

 was still visible, which became more distinct whenever the 

 scoria was moved, or the red hot lava in the interior exposed. 



Having ascertained that it was possible to approach within 

 four or five feet of the lava, and to examine the vapour imme- 

 diately close to the aperture, I returned the next day, having 

 provided the means of making a number of experiments on the 

 nature of the lava, and of the elastic fluids with which it was 

 accompanied. I found the aperture nearly in the same state 

 as the day before, but the lava spread over a larger surface, 

 forming an eddy in the hollow of the rock, over which it fell, 

 from which it could be raised in an iron ladle more easily than 

 from the current, and where there was much more facility of 

 placing and withdrawing substances intended to be exposed 

 to its agency. 



One of the most important points to be ascertained was, 

 whether any combustion was going on at the moment the lava 

 issued from the mountain. There was certainly no appearance 

 of more vivid ignition when it was exposed to air, nor did it 

 glow with more intensity when it was raised into the air by an 

 iron ladle. I put the circumstance, however, beyond the possi- 

 bility of doubt : I threw some of the fused lava into a glass 

 bottle furnished with a ground stopper, containing siliceous 

 sand in the bottom : I closed it at the moment, and examined 

 the air on my return. A measure of it mixed with a measure 

 of nitrous gas gave exactly the same degree of diminution as 

 a measure of common air which had been collected in another 

 bottle on the mountain. 



I threw upon the surface of the lava nitre, both in mass and 

 in powder. After this salt had fused, there was a little in- 

 crease of vividness in the ignition of the lava, but much too 

 slight to be referred to pure combustible matter in any quan- 

 tity ; and on making the experiment on a portion of lava taken 



up 



