112 



J. W. Judd — On Volcanos. 



yellow colour, but sometimes exhibiting a bright red tint, com- 

 municated to them by the sulphide of arsenic (Kealgar). 



The distinguished chemists, who at the instance of the French 

 Academy have studied the gases discharged from volcanic vents, 

 have accumulated a large body of valuable information on this 

 interesting subject. Vulcano affording such remarkable facilties 

 for their investigation, has received much attention from MM. 

 Charles Sainte-Claire Deville, Leblanc and Fouque. Their con- 

 clusions it would be impossible to detail, much less to discuss the 

 bearings of upon geological questions, in the present sketch. Some of 

 the more important facts obtained may, however, be briefly noticed. 



The elements which have been detected among the gaseous ema- 

 nations of Yulcano are as follows : — oxygen, hydrogen, nitrogen, 

 chlorine, iodine, sulphur, selenium 1 (first detected by Stromeyer in 

 1825), phosphorus, arsenic, and boron ; and the presence of bromine 

 is suspected though not proved. The most remarkable circumstance 

 is the abundance of boron in these emanations ; this element not 

 being an ordinary product of volcanic action, though found so 

 abundantly in the hot springs of Tuscany. 



It has been clearly shown that the nature of the gases evolved 

 varies with the temperature of the fumaroles. This fact is illus- 

 trated by the following table, in which I have placed side by side a 

 number of the analyses made by M. Fouque : 





a. 



b. 



c. 



d. 



e. 



/ 



Sulphurous and "> 

 Hydrochloric acids, j 

 Carbonic acid 



73-80 



2340 



traces . 



0-52 



2-28 



66-0 



12-0 



10-0 



2-4 



9-6 



34-0 



28-0 



12-0 



4-8 



21-2 



27-19 



59-62 

 0-0 

 2-20 



10-99 



7-3 



68-1 



10-7 



2-7 



11-2 



0-0 

 63-59 



Sulphuretted Hydrogen 



traces 

 7-28 





29-13 







a. was from a strongly acid fumarole, with a temperature of 

 360° C, which deposits sulphide of arsenic, chloride of iron, and 

 chloride of ammonium towards its centre, and boracic-acid and 

 sulphur at greater distances. 



b. was from a similar fumarole, but with a temperature of only 

 250° C. 



c. was similar to a and 6. 



d. deposited similar salts to the former, but its temperature was 

 only 150° C. 



e. was from a slightly acid fumarole, with a deposit of chloride 

 of ammonium, sulphur, and boracic, acid, and a temperature of only 

 100° C. 



/. was similar to e. 



Sulphur appears to be deposited round volcanic fumaroles through 



1 The mixture of sulphur and selenium deposited here received from Haidinger 

 the name of " Volcanite." 



