meunier: formation of magmatic gases 217 



solvent along with it and causes it to be spurted out to a greater or 

 less distance. That ejection might even take on all the leading 

 characters of a volcanic eruption, if the ordinary stopcock, which 

 curves downward, were replaced by a straight tube pointing 

 upward. In that case a veritable spray of water would be seen 

 spurting forth, just as a veritable spray of lava spurts forth from 

 a crater. This spray of lava, called ashes because of its color, 

 occurs when the projected liquid is solidified so rapidly that the 

 rock has not time to crystallize but assumes the vitreous state 

 and reproduces the phenomena of Prince Rupert drops when 

 suddenly broken. 



If we suppose our soda-water spray to be produced in a space 

 with sufficiently low temperature, it will fall in the shape of 

 extremely fine ice-dust, which would correspond to the volcanic 

 ashes. If, howevea', the siphon be left open, it can not keep up 

 the ejection of this spray indefinitely. Soon the gas escaping 

 from occlusion, issuing with less violence, will carry the liquid 

 with it more sluggishly, till finally it merely drivels over the mouth 

 of the bottle and runs over the table along the slope presented by 

 the latter. In that condition it represents the lava flow issuing 

 from the volcano. In both cases it will be found that the emis- 

 sion of gases does not stop at once. If you hold your nose close 

 to the liquid bubbling out of the bottle, you will feel the prickling 

 characteristic of carbonic acid. Similarly, the coulee of Vesuvius 

 or Etna will continue for some time to emit jets of vapor, which, 

 by reason of their complexity, in contrast with the simplicy of 

 the carbonic acid, have deposited all the characteristic coatings 

 of fumaroles. 



Carrying the comparison still further, we may subject a soda- 

 water siphon to cooling till the liquid therein is reduced to a lump 

 of ice. It will then be noticed that cavities are formed, especially 

 in the upper part of the lump of ice, which represent the casts, as 

 it were, of the bubbles of gas relinquished by the solvent and re- 

 tained by its solidification. An important fact will then be ob- 

 served, namely, that the siphon may be opened with impunity; 

 no ''eruption" takes place. This is strictly analogous to the 

 history of the volcano. Our lump of ice resembles in many 



