SULPHUREOUS SPRINGS. 23 



for it appears that the hot springs themselves are subject 

 only to imperceptible variations. All these springs are 

 slightly impregnated with sulphuretted hydrogen gas. The 

 fetid smell, peculiar to this gas, can be perceived only by 

 approaching very near the springs. In one of these wells 

 only, the temperature of which is 56*2, bubbles of air are 

 evolved at nearly regular intervals of two or three minutes. 

 I observed that these bubbles constantly rose from the same 

 points, which are four in number ; and that it was not pos- 

 sible to change the places from which the gas is emitted, by 

 stirring the bottom of the basin with a stick. These places 

 correspond no doubt to holes or fissures on the gneiss ; and 

 indeed when the bubbles rise from one of the apertures, the 

 emission of gas follows instantly from the other three. I 

 could not succeed in inflaming the small quantities of gas 

 that rise above the thermal waters, or those I collected in 

 a glass phial held over the springs, an operation that ex- 

 cited in me a nausea, caused less by the smell of the gas, 

 than by the excessive heat prevailing in this ravine. Is this 

 sulphuretted hydrogen mixed with a great proportion of car- 

 bonic acid or atmospheric air? I am doubttul of the first 

 of these mixtures, though so common in thermal waters ; for 

 example at Aix la Chapelle, Enghien, and Bareges. The 

 gas collected in the tube of Fontana's eudiometer had been 

 shaken for a long time with water. The small basins are 

 covered with a light film of sulphur, deposited by the sul- 

 phuretted hydrogen in its slow combustion in contact with 

 the atmospheric oxygen. A few plants near the springs 

 were incrusted with sulphur. This deposit is scarcely 

 visible when the water of Mariara is suffered to cool in aii 

 open vessel ; no doubt because the quantity of disengaged 

 gas is very small, and is not renewed. The water, when 

 cold, gives no precipitate with a solution of nitrate of copper; 

 it is destitute of flavour, and very drinkable. If it contain 

 any saline substances, for example, the sulphates of soda or 

 magnesia, their quantities must oe very insignificant. Being 

 almost destitute of chemical tests,* we contented ourselves 



A small case, containing acetate of lead, nitrate of silver, alcohol, 

 prussiate of potash, &c., had been left by mistake at Cumana. 1 evapo. 

 rated some of the water of Mariara, and it yielded only a very small 

 residuum, which, digested with nitric acid, appeared to contain only 

 little silica and extractive vegetable matter. 



