Page:Popular Science Monthly Volume 51.djvu/730

714 Vincey, of the French School of Agriculture, as hygienically and economically the most perfect. The work is done through the nitric oxidation of nitrous organisms effected, independent of vegetation, by special microbes contained in the soil. The nitrates thus formed, combined with the very soluble bases contained in the earth, are taken up as foods by plants or carried off in drainage waters. The purifying quality of the soil is not augmented by the production of crops upon it. The siliceous sewer beds of Gennevilliers, near Paris, dug up and ridged, without crops, are capable of absorbing and purifying 1,200,000 cubic metres of sewage per hectare (about two acres and a half) a year. Agriculture is regarded as of great importance in the economy of sewer beds, but not so much on account of its relations to purification as to the quantity of water which the ground can receive. The demands which the most thirsty crops can make upon the water constituents of sewage are, however, limited; and they absorb only a fraction of the amount poured upon the beds. M. Vincey's observations in the Agricultural Park of Asnières indicate that forest land is capable of usefully purifying at least as much water as the natural meadow; and it results from all the experiments that, for a like soil and equal volumes of sewage, a smaller surface of meadow or forest is required than, for instance, of kitchen-garden crops. Siliceous soils and sands free from marl appear to have the highest purifying qualities. Limestone formations, marls, clays, etc., are inferior in these properties. The longer a soil has been purifying sewer water, the fitter it becomes for continuing the work; for purifying irrigation multiplies the colonies of mineralizing ferments in the soil. Comparative examination of land in which the operation had been going on from ten to twenty years and of soil that was virgin to the process, showed that no nitrogen had accumulated in the earth in consequence of sewage irrigation. The smaller part of the mineralized matter passes into the crops, while the larger part is washed away.

Cycles and Dogs in War.—The utility of bicycles in military art having been demonstrated, men of war are now studying the means of contending against them and their riders. The mere overthrow of the instrument does not convey any great advantage, for the man is there, and possibly still standing, armed, and ready to fight. Dogs have so far seemed to be the most effective agents in this contention, and the large Danish dog has been selected as the animal most fit. About a thousand dogs are said to be under training in Berlin for this sort of warfare. They are taught to distinguish the uniforms of friends—German, Austrian, and Italian—from those of the enemy—French and Russian—and attack the latter, the legs of the sham "hostile" soldiers being well protected, of course, by stout buskins. As all the armies will have cycle troops, they will all have to have their trained war dogs; and then, when the attack has commenced, La Nature slyly intimates, and the dogs get mixed with the cyclists, they will leave the soldiers and go to fighting one another.

Hydraulic Blasting.—A meeting of the Manchester Geological Society is reported in Industries and Iron, at which a new hydraulic apparatus for breaking down coal in mines was discussed. Mr. James Tonge, who described the apparatus, called attention to the great danger attending the ordinary method of blasting in coal mines, and said that the numerous serious accidents from this cause had led the inventors to look for a safer process of loosening the coal. The new apparatus consists of a hydraulic cartridge, eighteen inches in length and three in diameter, and weighing thirty pounds, and a small but powerful hand pump fitted with a pressure gauge weighing about twenty pounds. The mode of using it is as follows: The coal is holed underneath the usual depth, and a hole drilled near the roof to about the same depth as the holing, in the same way as for blasting. After this the cartridge is placed in the hole and pushed to the back. No "stemming" is required. The pump is coupled to the cartridge, the suction pipe placed in a small bottle of water, and work commences. Very soon the gauge begins to show the rising pressure—half a ton, a ton, a ton and a half, two tons to the square inch. During this time a cracking sound is heard, indicating the shearing off of the coal at the back. The gradual way in which the work is done, without shock