312 Reviews — Dr. A. Bran's Volcanic Researches. 



settled with extreme slowness. Photographs show the author wading 

 through such emulsions well over his ankles. At a distance from the 

 crater, for example at Pompeii, the ash fell with 0-1 per cent, water 

 and was sufficiently moist to retain a finger-print. This increasing 

 water content depends upon the presence of the hygroscopic chlorides 

 Fe Cl 3 , Mg Cl 2 , etc. Where it has 0-2 per cent, water the ash 

 agglutinates into little spheres. The hygroscopic character of the ash 

 is well shown by the following experiment. After careful drying the 

 ash is exposed to a moist atmosphere saturated at 20° C. (P. = 780 mm.). 

 It absorbs — 



In 5 minutes . . . . 0'13 per cent, of water. 



» 15 .... 0-30 



,, 60 .... 0-90 



Those who maintain tiie orthodox aqueous theory of volcanic 

 explosions must suppose that the ash falling near the crater was too 

 hot during its transit to absorb any of the water-vapour by which it 

 was propelled. This involves another difficulty : the ash when it 

 falls is white, but it can be shown experimentally that owing to its 

 content of ferrous chloride, it reddens immediately if exposed to the 

 action of water-vapour at a high temperature. 



2. In the mass of the cone and in the crater the salts Fe 3 Cl G , 

 Fe Cl 3 , Mg CI 3 , and Al 3 Cl 6 may be collected dry and undecomposed, 

 although at low temperatures they are deliquescent, while at 300° C v 

 water-vapour transforms them instantaneously into Fe 3 3 , Mg O, and 

 Al 3 3 . 



3. One day during the eruption drops of moist clay did indeed fall 

 at Resina ; at other places, however, the ash was dry. The local 

 nature of the phenomenon points to the atmosphere as the source of 

 the water in this particular case. The very darkness due to a cloud 

 of ash is in itself a provocative cause of rain, owing to the fall in 

 atmospheric temperature involved ; thus Brun and Montagnier have 

 observed drops of clay during a sandstorm at the Bay of Peneda, 

 Lanzarote, one of the Canary Islands, whither we may now follow 

 our indefatigable guide. 



Brun went to the Canaries with Montagnier on purpose to study 

 volcanoes in a typical arid region. Solfatara were found on the Sugar 

 Loaf of Tenerife. Those of the crater had a temperature of 83° C, 

 and liberated gases which, when deprived of water, had a percentage 

 volume composition of about 67 per cent. C0 3 , 4 per cent. 3 , and 

 29 percent, unabsorbable gases (nitrogen, etc.). The water saturated 

 the fumaroles after showers of rain, and in fact occurred as drops 

 carried in the stream of gas; at other times its amount was insufficient 

 to maintain saturation. 



Timanfaya, in Lanzarote, proved exceptionally interesting. Bain 

 falls but once a year in this island, and at the time of Brun's visit, in 

 mid-September, 1907, the last rain had fallen on April 27, and had 

 continued for four hours only. 



The cone of Timanfaya is a mass built up of lapilli, dating from the 

 eruption of 1730-6, and is still warm (1907). Where the tempera- 

 ture is highest the pebbles are cemented into a reddened crust 

 10 cm. deep. The base of this crust is covered with a thin green 



