Volcanic Dust which fell in tJte Orkney Islands. 219 



to arise from differences in the nature of the materials of the 

 several volcanoes. Vauquelin found that the ashes ejected 

 from Vesuvius in 1822 gelatinized with acids. He obtained 

 from them, 55 per cent, of silica, 15 of alumina, and 16 

 of oxide of iron, besides potash, lime, and small quantities of 

 soluble salts and carbon.* Dufrenoy found the ashes of 

 Guadaloupe and of Mexico to be so much acted on by acids, 

 as to admit of a separation of the subject of analysis into 

 portions soluble in acids and portions insoluble.! His results 

 were as follows, moisture having been previously expelled by 

 ignition : — 



Dufrenoy also found in the Guadaloupe ashes of 1797 

 about 2^ per cent, of soluble sulphates ; and in those of 

 1836 about ^ per cent, of sulphur.J 



* Ann. de Chim. et de Phys., xxv., 72. 



t Annales des Mines, 3d Series, xii., 355. 



+ The following is extracted from the public papers : — " During Sep- 

 tember and October, Hecia was in eruption, and this circumstance was 

 indicated as follows : — 



*' On the night of 2d September, the largest of the Orkney Isles was, 

 during a violent storm, covered with fine ashes, resembling ground 

 pumice-stone. The report continues : The only way of accounting for 

 it, is by supposing that Mount Hecla has had an eruption, as the wind 

 was exactly from that quarter, and it is quite evident that the dust is 

 volcanic. Dr Barry, in his History of Orkney, says, that in 1783, the 

 last dreadful eruption of Mount Hecla, the dust fell on Orkney in the same 

 manner, being thus carried upwards of 400 miles." 



Intelligence from Copenhagen next confirmed the above conjecture. 

 On the same, or the following night, the crew of a vessel, bound from 

 that port to Reikiavik, observed, whilst about eighteen English miles 

 from land, volcanic flames on the southern coast of Iceland. On the 3d, 

 two vessels near the Faroe Islands were also covered with ashes. 



