F. A. Ferret — Vesuvius. 421 



Secondary fumaroles formed in considerable numbers on the 

 sub-terminal flows of 1905-6 on the west-northwest flank, the 

 temperatures of which are recorded in the preceding section. 

 For some time prior to the spring of 1909 chlorides and sul- 

 phates were deposited by some of these, but since then the 

 emanations have been neutral, and the majority have been 

 remarkable as mere purveyors of heated air. Ever since the 

 eruption the large amount of water vapor given off by these 



Fig. 7. 





r ^ - — 









riWI 





^^^^R^~ -j 



Ja 





£&r^ 





pp 







t 



tftm&ntk* 



1 















Fig. 7. Collecting gases from a furnarole at a temperature of 438° C. 



fumaroles after rain has produced the appearance by day of an 

 active lava stream.* 



Far different from these are the primary fumaroles on the 

 northern flank of the cone, which are in communication with 

 an important system of Assures formed in the mountain side 

 during the eruption. They have been notable for their fairly 

 high temperature ever since the eruption, and I have con- 

 stantly insisted upon their importance. Early in 1908 I found 

 323° C. at one of these, and commenced a series of compara- 

 tive observations which has several times been broken off in 

 consequence of the destruction of the fumaroles by individuals 

 who make a business of selling the minerals of the volcano. 



The largest of the fumaroles has, until recently, remained 

 intact. On March 5, 1908 the temperature here was 314° C, 



* These vapors exhibit the well-known effect of increased visibility on the 

 application of a lighted match. 



