Page:Popular Science Monthly Volume 55.djvu/885

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863
FRAGMENTS OF SCIENCE.

test. But mining engineers and prospectors are learning that in a mineralized region gold may occur in any rock, and hundreds of prospectors are assaying all sorts of most unpromising-looking rock, satisfied that by assay alone can they determine whether a certain rock is gold-bearing or not. This persistent and more or less systematic work now going on in every mining district must result in the discovery of many valuable deposits in unexpected localities, and ultimately promises to add largely to the annual output of gold."


MINOR PARAGRAPHS.

The investigations of F. E. L. Beal of the Food of Cuckoos and S. D. Judd of the Food of Shrikes in their relation to agriculture are published in a single bulletin by the Department of Agriculture. Mr. Beal finds that the food of cuckoos consists almost wholly of insects, of which he has found sixty-five species in their stomachs, and concludes that from an economical point of view they rank among our most useful birds; and, in view of the caterpillars they eat, it seems hardly possible to overestimate the value of their work. Mr. Judd finds, from a very extensive examination, that the food of butcher birds and loggerhead shrikes consists of invertebrates (mainly grasshoppers), birds, and mice. During the colder half of the year the butcher bird eats birds and mice to the extent of sixty per cent, and ekes out the rest of its food with insects. In the loggerhead's food, birds and mice amount to only twenty-four per cent. Its beneficial qualities "outweigh four to one its injurious ones. Instead of being persecuted, it should receive protection.

The Engineering Magazine is authority for the following: "The wrecking of the steamship Paris on the coast of Cornwall and the difficulties encountered in attempting to save her while a number of her compartments forward are filled with water, lead Mr. Richards, in the American Machinist, to suggest the applicability of compressed air. 'There is a means of expelling the water from the filled compartments so obvious, and so certainly effective, that it seems unaccountable that some engineer has not suggested it before this. Close the hatches of the flooded compartments and drive the water out by forcing air in. It would not make the slightest difference how big the holes might be in the bottom, as the water would be expelled and kept out on the same principle as in the old-fashioned diving bell.' This suggestion carries with it a much larger and more important one—namely, the use of air pumps instead of water pumps to save a leaking ship while afloat. As Mr. Richards well remarks, the work of trying to pump out a leaky ship is not only enormously wasted while it is going on, but it is never finished. If, however, the water leaking into a compartment of a ship be expelled by pumping air into the space, the work is done so soon as the compartment is filled with air down to the level of the leak. After that point is reached the ship is safe, no matter how large the hole, and no further pumping is necessary."

Chlorate of potash has always been regarded by manufacturers and chemists as a nonexplosive, and hence there has been little care taken in handling and storing it. A recent explosion, however, at a large chemical works at St. Helens, in England, seems to disprove this view. A storehouse containing about one hundred and fifty tons of chlorate in the form of both powder and crystals took fire, and almost immediately after the falling in of the roof an explosion of terrible violence occurred, the shock being felt over a distance of twenty miles. The chlorate works were entirely demolished. A large gas holder of the city gas works, containing two hundred and fifty thousand cubic feet of gas, was burst and the gas ignited. Eight hundred tons of vitriol was poured into the streets of the town by the wrecking of ten vitriol chambers in a neighboring alkali works. Houses were unroofed, and in the main streets of the town, a quarter of a mile away, nearly every plate-glass window was demolished. A theory accounting for the explosion, advanced by Mr. J. B. C. Kershaw, in the Engineering and Mining Journal, is that it was due to the sudden and practically simultaneous liberation of all the oxy-