88 Sir H. Davy on the Phenomena of Volcanoes. 



up in the ladle, it appeared that the disengagement of heat 

 was partly owing to the peroxidation of the protoxide of iron, 

 and to the combination of the alkali of the nitre with the earthy 

 basis of the lava ; for where the nitre had melted, the colour 

 had changed from olive to brown. This conclusion was still 

 further proved by the circumstance that chlorate of potash 

 thrown upon the lava did not increase its degree of ignition so 

 much as nitre. When a stick of wood was introduced into a 

 portion of the lava so as to leave a little carbonaceous matter 

 on its surface, nitre or chlorate of potassa then thrown upon 

 it caused it to glow with great brilliancy. Some fused lava 

 was thrown into water, and a glass bottle filled with water held 

 over it to collect the gas disengaged ; it was in very minute 

 quantity only, and when analysed on my return proved to be 

 common air a little less pure than that disengaged from the 

 water by boiling. A wire of copper of g^th of an inch in 

 diameter, and a wire of silver of ^th, introduced into the lava 

 near its source, were instantly fused : an iron rod of }th of an 

 inch, with a piece of iron wire of about y \jth, were kept for 

 Ave minutes in the eddy in the stream of lava ; they were not 

 fused ; they did not produce any smell of sulphuretted hydro- 

 gen when acted on by muriatic acid. A tin-plate funnel filled 

 with cold water was held in the fumes disengaged with so much 

 violence from the aperture through which the lava issued : 

 fluid was immediately condensed upon it, which was of an acid 

 and subastringent taste. It did not precipitate muriate of 

 baryta ; but copiously precipitated nitrate of silver, and ren- 

 dered the triple prussiate of potassa of a bright blue. When 

 the same funnel was held in the white fumes above the lava 

 where it entered the bridge, no fluid was precipitated upon it, 

 but it became coated with a white powder which had the taste 

 and chemical qualities of common salt, and proved to be this 

 substance absolutely pure. A bottle of water holding about 

 | of a pint, with a long narrow neck, was emptied immediately 

 in the aperture from which the vapours pressing out the lava 

 issued, and the neck was immediately closed. This air ex- 

 amined on my return was found to give no absorption with 

 solution of potassa ; so that it contained no notable proportion 

 of carbonic acid, and it consisted of 9 parts of oxygen and 91 

 of azote. There was not the least smell of sulphurous acid in 

 the vapour from the aperture, nor were the fumes of muriatic 

 acid so strong as to be unpleasant ; but during the last quarter 

 of an hour that I was engaged in these experiments, the wind 

 changed, and blew the smoke from the crater upon the spot 

 where I was standing : the sulphurous acid gas in the fumes 

 was highly irritating to the organs of respiration, and I suf- 

 fered 



