32 On Tropical Miasmata. 
diluted, provided that they are not exhaled in recesses or in 
enclosed spaces, which do not at all, or but slightly, partake 
of the external movements of the air. With respect to car- 
bonic acid gas, there are many instances of this kind in the 
neighbourhood of the Laacher Sea. I was many times in the 
neighbourhood of the village of Wehr, on a large plain, most 
likely an old crater of an extinct voleano, where carbonic acid 
gas is evolved in immeasurable quantities from hundreds of 
acidulous springs close to one another, and where, at many 
points, bubbles as large as the head scatter the water toa 
height of more than a foot. Nevertheless, in the middle of 
the marsh, the smell of the gas is hardly, but that of the 
marshly exhalations very distinctly, perceptible. From this 
it is to be seen that gases are by far more easily distributed 
throughthe atmosphere, than exhalations of putrefying matters. 
“In applying these observations to the exhalations of sul- 
phuretted hydrogen from the water on the coast of Africa, it is 
obvious that they, when even yet so considerable, will hardly 
affect a ship’s company. But the exhalations of putrefying 
matters doubtless bear quite another relation to those exposed 
to them. 
‘J think it will be found that the sea-water in that country 
will contain far less sulphuretted hydrogen than that analyzed 
by Professor Daniell, and that this gas for the most part has 
been produced during the carriage of the waters to England. 
Indeed, the vegetable matter found in different proportions in 
all those waters which contained sulphuretted hydrogen, seems 
to be the remaining part of what has been decomposed by the 
sulphatesinthem. All those waters were bottled in the months 
of September, October, and November, 1839. The Reports 
of Professor Daniell are dated on the 13th April 1840 ; when, 
therefore, the analysis of them was made, they had been pre- 
served in the bottles above half ayear. This space of time 
is, however, according to my researches, more than sufficient 
to effect decompositions of sulphates by vegetable matters. 
Besides, according to the experiments of Professor Daniell, 
mentioned in No, 4 of The Friend of Africa, three months are 
alone sufficient to produce sulphuretted hydrogen, by adding 
a quantity of newly-fallen leaves to water, in which sulphate 
