FROM CHAOS TO CORAL.

New Zealand Times, Volume XXX, Issue 4432, 3 June 1875, Page 3

FROM CHAOS TO CORAL.

(From the Scientific American.) Many of our i;eaders doubtless have noted, perhaps, during the study of experimental chemistry, that silver, when melted and afterwards allowed to solidify in an earthen crucible, will, as it cools, assume a brisk effervescence. The mass bubbles and swells ; small particles are thrown out of the pot, and, in fact, a miniature volcanic eruption is reproduced ; to complete the resemblance to which the silver, when solid, appears covered with little cones pierced at the centre, simulating the forms of volcanoes. This phenomenon, however, we can easily account for from the knowledge that gases ai-e absorbed not only by liquids at the ordinary temperature, but by. melted bodies. The silver absorbs oxygen, which it abandons on cooling ; the mere sudden the latter the greater the disengagement of the gas ; while, on the other hand, if the metal be allowed to get cold slowly, the oxygen escapes insensibly and hardly disturbs the surface. Melted litharge also absorbs oxygen, and similarly abandons it. A like absorption takes place in the combustible gases which are found in the furnaces for melting metals, and recent investigations iu France have proved that cast iron, after cooling, retains a notable quantity of gas, especially of carbonic oxide and hydrogen. While, however, totally melted bodies absorb gases and reject them at the moment of cooling, the same bodies, when simply softened by the action of heat (though absorbing gases as before), retain the gases after becoming cool, and give them off slowly under the influence of a new elevation of temperature, and of an almost perfect vacuum. These facts are not only very curious, but are of considerable importance from a geological point of view. Volcanoes, it is known, when in eruption emit various gases ; first hydrocloric acid, sulphuric acid, and hydrosulphuric acid ; later, the carburetted hydrogens predominate ; and finally appears a disengagement of carbonic acid, which lasts for centuries. The volcanoes of Auvergne, 1 in France, have been extinct for thousands of years, and yet springs charged with carbonic acid are abundant in the vicinity. There are other well-known instances, such as the celebrated Dog Grotto, near Naples, so called from the practice of lowering unhappy dogs into its depths to see them overcome by the deleterious gas, and the Guevo Upas, or poisonous valley of Java, where the atmosphere is so deadly that the soil is said to be covered with the bones of animals aud of men who have died from its effects ; in both of which the discharge of gas has existed from time immemorial. Humboldt counted 407 volcanoes on the earth, of which 225 only were active. This latter number has since been increased to 270, of which 190 are on the islands or shores of the Pacific. The majority of volcanoes are situated near the great fracture •which extends along the coast of the American continents and is prolonged to Kamschatka, to Japan, and as far as Java and Sumatra; others are located in New Zealand, New Britain, the New Hebrides, New Caledonia, and in the antarctic regions, Mounts Erebus and Terror. The quantity of carbonic acid disengaged by these vast furnaces is enormous. Boussingalt estimates it at 95 per cent. of their entire gaseous emission, and this has been verified by Bunsen in investigations upon the emission of Mount Heola. Here, then, is an immense and apparently inexhaustible series of reservoirs, which form the source of a large amount of the carbonic acid in the world. It remains to examine how this supply was generated ; and the theory which has been proposed is readily followed. When the earth cooled down from its molten state, the various substances, which were maintained separate by the excessive temperature, became united according to their respective affinities : hydrogen and oxygen formed water ; oxygen and carbon, carbonic acid ; chlorine and sodium, sea salt, aud so on. The incandescent rocks, however, while still liquid, found themselves in contact with a dense atmosphere containing various gases, which they absorbed in exactly the same manner as we have stated the silver and letharge to act as regards oxygen and iron in reference to carbonic oxide aud hydrogen. Further, it was possible that these rocks should become charged in a greater degree with carbonic acid than with other gases existing in the atmosphere through the action of a relative affinity, just as the melted silver absorbs oxygen instead of nitrogen, though both are present in the same, atmosphere. As commotions on the surface of the globe were frequent in the transition state, the rocks were perpetually changing places. Vast masses would be engulphed, to be replaced by others rising from the depths, and so an incredible quantity of carbonic acid became occluded in their substance. As these rooks solidified, the oarbonic acid slowly escaped ; and if, as is proved, with reasonable probability, there still exists in the interior of our globe an incandescent mass which is constantly cooling, here, then, is the source of the disengagement of the gas which, escaping through the volcanic apertures, mingles with our atmosphere. It is curious in thus tracing the part which the extinct volcanoes play in the economy of our globe, to note how perfectly the migration, which the carbonic acid that they evolve may assume, illustrates the truth of the indestructibility of matter. First found in the primitive atmosphere of our earth, it beoame_ absorbed by the incandescent rooks, and remains buned in their depths for thousands of years.. Little by little, however, as its captors become colder, it makes its way from its subterranean prison, and escapes into our atmosphere. Its liberty is, however, of short duration, for the ram again seizes it and carries it perhaps to the rivers, aud the latter to the sea. hiom the water it is wrested by lime to form a carbonate, which minute animal cuke —the coral insects, working tirelessly century after century—build first into a reef and then into an island, forming, perhaps, the nucleus of a new continent to be completed in the ages far in the future.