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Updated: May 20, 2025
Pyrites dispersed in quartzose veins, crossing the mica-slate, are often auriferous, no doubt; but no analogous fact leads to the supposition that the sulphuretted iron which is found in the schistose marls of the alpine limestone, contains gold. Some direct experiments, made with acids, during my abode at Caracas, showed that the pyrites of Cuchivano are not auriferous.
In several spots of the valley of Caracas, the gneiss contains a small quantity of gold, disseminated in small veins of quartz, sulphuretted silver, azure copper-ore, and galena; but it is doubtful whether these different metalliferous substances are not too poor to encourage any attempt at working them.
The residue dissolved in water, filtered, and tested with copper-foil, etc. Tests. The following table gives the action of corrosive sublimate with reagents: 1. With iodide of potassium Bright scarlet colour. 2. With potash solution Bright yellow colour. 3. With hydrochloric acid and First a yellowish and then a black sulphuretted hydrogen colour. 4.
The able chemists above mentioned were, like myself, struck with the extreme purity of the hot waters that issue from the primitive rocks of the basin of Aragua. Those of Onoto, which flow at the height of 360 toises above the level of the sea, have no smell of sulphuretted hydrogen; they are without taste, and cannot be precipitated, either by nitrate of silver or any other re-agent.
The flame, when it does make its appearance, is very smoky and gives little light, because, in addition to the coal gas of commerce, there are present ammonia gas, sulphuretted hydrogen, carbonic acid, tar vapour, etc., which prevent brightness of flame. A miniature gasworks, if it is to be worthy of its name, must obviously endeavour to separate the troublesome components from the useful gas.
The waters, which are loaded with sulphuretted hydrogen, issue from a quartzose sandstone, lying on compact limestone, the same as that we had examined at the Morro. We again found in this limestone intercalated beds of black hornstein, passing into kieselschiefer. The real kieselschiefer and Lydian-stone have not been observed hitherto except in the transition-slates and limestones.
It is nearly surrounded by a broad belt of papyrus, so dense that we could scarcely find an opening to the shore. The plants, ten or twelve feet high, grew so closely together that air was excluded, and so much sulphuretted hydrogen gas evolved that by one night's exposure the bottom of the boat was blackened. Myriads of mosquitoes showed, as probably they always do, the presence of malaria.
I will, lastly, give you a test that will be useful in your own homes to detect minute quantities of lead in water running through lead pipes. Place a large quantity of the water in a glass on a piece of white paper, and add a solution of sulphuretted hydrogen and let stand for some time. A brown colour denotes lead.
Heated in substance, it crepitates and chars; and if heat be increased, the metal is deposited. Treated with sulphuretted hydrogen, a characteristic orange-red sulphide is formed. A drop of the solution evaporated leaves crystals, either tetrahedric, or cubes with edges bevelled off. Sulphuretted hydrogen passed through gives the orange-red precipitate above named.
All delicate animals must be intrusted one by one to their new home, and carefully watched for deaths and decay, which, whether arising from dead plants or animals, ruin everything very quickly, unless they be promptly removed. For sulphuretted hydrogen, even in very minute quantities, is sure death to all these little creatures. The emanations from paint and putty are often fatal in new tanks.
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