Page:Popular Science Monthly Volume 1.djvu/389

Rh exposure to weather is considerable, far greater, indeed, than is generally known. The results of his analyses show in some cases a total loss in weight of a specimen, from this cause, amounting to 33.08 per cent., while its deterioration in quality, for purposes of fuel or gas-making, reached a still higher figure. This change consists in a slow combustion, in which the volatile constituents—which are most valuable combustible elements are gradually eliminated, while the relative proportions of carbon-ash and sulphur are comparatively augmented. It might be expected, now that the nature of this change is indicated, that anthracite (which has already gone through a very similar process in becoming what it is by the loss of its bituminous matter) should suffer least of all coals from this action, and the result of analysis shows this to be the case. The density and compactness of this variety, aside from its chemical character, protect it in no inconsiderable degree. The cannel coals rank next in their power to resist deterioration from this source, while the bituminous varieties are the most susceptible. The experiments of Dr. Yarrentrapp are of such direct and practical importance that all who are engaged in the mining, transportation, storage, or consumption of coal, can study them with profit. It appears from accurate tests of a number of samples before and after exposure, that all the valuable properties of the coal had deteriorated. The coking quality of the weathered coal diminishes with its gas-yielding quality, the author informing us that a sample of coal, yielding when freshly mined a firm, coherent coke, after eleven days' exposure yielded a coke of no coherence, and in all the samples tested the rule was absolute that the longer the coal had been exposed the greater was the inferiority in the quality of the coke it produced. The gas-yielding quality decreased in one instance 45 per cent., and the heating power 47 per cent.; while the same sample under cover lost in the same time but 24 per cent, for gas purposes, and 1 2 per cent, for fuel. These experiments go far to explain the almost universal inferiority of the Black or waste coals in heating power when prepared for burning, even though some combustible material like pitch or tar is used in their cementation. It indicates, too, the imperative necessity of keeping coals amply protected from the deteriorating action of the air and moisture, by keeping them constantly dry and under cover.

Anecdotes of Rats.—A gentleman, who has passed many years of his life at St. Helena, told me lately several stories about rats, so curious that I thought them worthy of record. He said that at one time the common brown rat was extremely common all over the island, in fact, a perfect pest; and, to avoid its attacks, his father had constructed a large store, rat-proof; i. e., a rat once in could not get out again. A number, however, came in with produce and goods from the ships, and bred there. Around this store were Venetian blinds to the windows, and one day one of his men, when it was raining, watched a rat sitting on the Venetian, and putting out his tail to collect on it the drippings of water at the edge; he then withdrew it and licked it. The servant told his master, who immediately understood that the rats could get no water inside the store, and therefore directed that a butter firkin should be cut down to four or five inches, and in the top a large circular wire rat-cage trap should be fixed. Several small planks were placed for the rats to get up to the entrance to the cage, which exactly fitted the firkin. No food would have induced the rats to enter the trap, but water did, and many were thus captured. When caught they were given to the dogs; but there was one rat which would not leave the trap for many days. He was well identified day by day, till, becoming incautious, he leaped down, and was immediately killed. There is one peculiarity with these rats, viz., their very often building or making their nests in the trees. I have in India several times found rats'—nests in trees; but then they have always been stolen nests, such as deserted abodes of the squirrel or sparrow; but here my friend, who is no naturalist, tells me that they construct them principally of fir spines, on the ends of the boughs, some twelve or fifteen feet from the ground, in the common fir-trees. The spots selected are just where the overlapping bough nearly meets the lower one. He said that all