ON ITS EXTERIOR. SPRINGS OF VAPOUR AND GAS. 213 



there was no known way of determining, in a mixture of 

 nitrogen and hydrogen, the relative proportions of each. 

 A method of doing this, so that an admixture of three 

 thousandths of hydrogen could be detected, was dis- 

 covered four years afterwards by Gray-Lussac and my- 

 self. ( 293 ) In the half century which has elapsed since 

 my visit to Turbaco and my astronomical survey of the 

 Magdalena Eiver, no traveller examined the above-de- 

 scribed small mud- volcanoes scientifically ; until, at the 

 end of December 1850, my friend Joaquin Acosta, ( 294 ) 

 who was acquainted with modern geology and chemistry, 

 made the important observation that, " at that time 

 the cones exhaled a bituminous odour; that some petro- 

 leum floated on the surface of the water in the orifices ; 

 and that the gas which rose from each of the volcancitos 

 was inflammable." Of all this there was no trace in my 

 time. Acosta asks whether these circumstances indicate 

 a real alteration produced in the phenomena by subter- 

 ranean processes, or whether the discrepancy arises 

 merely from error in the earlier experiments ? I should 

 have freely admitted the latter to have been a probable 

 explanation, if I had not preserved the leaf of the journal 

 in which I noted the experiments in detail on the 

 same morning on which they were made. ( 295 ) I find 

 nothing therein which could now give me any doubts 

 respecting them ; and the experience above alluded to, 

 i. e. that (according to Parrot's account) " the gas of 

 the mud-volcanoes of the peninsula of Taman had, in 

 1811, the property of preventing combustion; that a 

 glimmering splinter was extinguished in it ; and that the 

 bubbles which rose a foot thick, could not be made to 

 ignite in bursting," whereas at the same place, Gobel, 



