214 COSMOS. 



water, which rests upon a compact floor of mud. The erup- 

 tions are not simultaneous in neighbouring cones, but in 

 each one a certain regularity was observable in the periods 

 of the eruptions. Bonpland and I, standing on the outer- 

 most parts of the group, counted pretty regularly 5 eruptions 

 every 2 minutes. On beading down over the small orifice 

 of the crater a hollow sound is perceived in the interior of 

 the earth, far below the base of the cone, usually 20 seconds 

 before each eruption. A very thin burning wax taper was 

 instantly extinguished in the gas, which was twice collected 

 with great care ; this was also the case with a glowing chip 

 of the wood Bombax Ceiba. The gas could not be ignited. 

 Lime water was not rendered turbid by it ; no absorption 

 took place. When tested for oxygen with nitrous acid gas, 

 this gas showed no trace of the former in one experiment ; 

 in a second case, when the gas of the Yolcancitos had been 

 confined for many hours in a bell glass with water, it exhi- 

 bited ratter more than one hundredth of oxygen, which 

 had probably been evolved from the water and accidentally 

 intermixed. 



From these analytical results I then declared, perhaps not 

 very incorrectly, that the gas of the Volcancitos of Turbaco 

 was nitrogen gas, which might be mixed with a small 

 quantity of hydrogen. At the same time I expressed my 

 regret in my journal, that in the state of chemistry at that 

 time (April, 1801), no means were known by which, in a 

 mixture of nitrogen and hydrogen gases, the numerical 

 proportions of the mixture might be determined. The 

 expedient, by the employment of which three thousandths 

 of hydrogen may be detected in a gaseous mixture, was only 

 discovered by Gay-Lussac and myself four years afterwards, 69 

 During the half-century that has elapsed since my residence 

 in Turbaco, and my astronomical survey of the Magdalena 

 river, no traveller had occupied himself scientifically with 

 the small mud-volcanoes just described, until, at the end of 

 December, 1850, my friend Joaquin Acosta, 70 so well versed 



69 Humboldt and Gay-Lussac, Memoire sur ^analyse de I'air atmo- 

 spherique in the Journal de Physique, par Lametherie, t. Ix, p. 151 (see 

 my Kleinere Schriften, Bd. i, s. 346). 



70 " It is with emotion that I have just visited a place which you 

 made known fifty years ago. The appearance of the small volcanoes of 



