Page:Popular Science Monthly Volume 12.djvu/526

510 potash is a more powerful developing agent than ammonia; 3. That, so far from it being true that the most energetic form of development, when no soluble salt of silver is present, is that which depends on the use of free alkali, a most powerful development may be had without free alkali; 4. That ferrous salts do not act only in the presence of a soluble salt of silver. We have not space to describe the method followed by the author in his researches, but must content ourselves with simply stating the principal results, referring the reader who desires fuller information to the pages of our contemporary. Among the bodies found by Mr. Lea to possess the power of developing the latent image are sugars, manna being especially noteworthy as producing, under certain conditions, "an image as bold and strong as any substance hitherto known." Of the glucosides some give good images. Of several organic acids tried, only one, cevadic acid, exhibited tolerable developing power. The resins exhibit more or less developing power, guaiacum being nearly as energetic as pyrogallol itself. Among the essential oils, the oil of cloves yields a strong, clear image, and good results are also obtained from oil of Roman camomile and oil of peppermint. The organic bases exhibit little developing power. Concerning pyrogallol the author writes that with potassium formate it gives better results than with any other substance. A large number of vegetable substances were tried, with varying results. Finally, the author experimented with cuprous oxide and with ferrous salts: a colorless solution of the former in ammonia develops a strong image; but the salts of ferrous oxide "proved to be the most interesting and remarkable of all the bodies examined, in their action on the image."

Preservation of Wood by charring and tarring.—A writer in the Industrie-Blätter, in remarking on the methods of preserving wooden posts by charring and coating with tar, says that these methods are effectual only when both are applied. If the posts are only charred, the charcoal formed on the surface acts only as an absorber of moisture, and really hastens decay. By applying tar without previously charring, the tar only forms a casing about the wood. Timber that is exposed to the action of water or let into the ground should first be charred, and then while still warm should be treated with tar till it is fully impregnated. The acetic acid and oils contained in the tar are evaporated by the heat and only the resin left behind, which penetrates the pores of the wood and forms an airtight and water-proof coating. It is important to impregnate the posts a little above the line of exposure, for here it is that the process of decay affects the wood first, and where the break always occurs when a post is removed from the earth or strained in testing.

Earthworms in Agriculture.—That the earthworm is of great service to the agriculturist is shown by the author of a paper, the substance of which we find in Die Natur. Not only does the earthworm not attack or injure the roots of plants; on the contrary, it aids them in their growth by excavating passages through which they can penetrate into strata otherwise inaccessible to them. And, as the overground portion of a plant is always proportioned to the length and number of its roots, it is plain that the earthworm is of great benefit to the plants in its neighborhood. The author placed an earthworm in a flower-pot containing a growing Dracæna two and a half feet in height. The worm was left undisturbed for some time, and soon it was found that it had passed through itself at least one-half of the earth in the flower-pot. The soil was in this way improved, many insoluble constituents being rendered soluble. The author's conclusion was that, inasmuch as he could discover no injury done to the roots of the Dracæna, the worm had fed on the remains of plants in the earth, utilizing and decomposing them thoroughly.

Drowning-Accidents.—The advantages of "paddling" and "treading water," as a means of escaping from drowning when one is suddenly precipitated into deep water, are set forth by a writer in the Sanitary Record. The motions performed in the acts of paddling and treading require no previous instruction, and in the great majority of cases would save life. In swimming, the mouth