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 hubbies 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 ah-? 1 am doubtful 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 Eontana’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 an 
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 be 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 a 
little silica and extractive vegetable matter. 
