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THE POPULAR SCIENCE MONTHLY. 



potash is a more powerful developing agent 

 than ammonia ; 3. That, so far from it being 

 true that the most energetic form of devel- 

 opment, 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 con- 

 tent ourselves with simply stating the prin- 

 cipal results, referring the reader who desires 

 fuller information to the pages of our con- 

 temporary. 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 de- 

 veloping 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 ob- 

 tained from oil of Roman camomile and 

 oil of peppermint. The organic bases ex- 

 hibit little developing power. Concerning 

 pyrogallol the author writes that with potas- 

 sium formate it gives better results than 

 with any other substance. A large number 

 of vegetable substances were tried, with 

 varying results. Finally, the author experi- 

 mented 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 



Preservation of Wood by eh airing and 

 tarring. A writer in the Industrie-Matter, 

 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 impreg- 

 nated. 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 air- 

 tight and water-proof coating. It is impor- 

 tant 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 ag- 

 riculturist 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 inacces- 

 sible to them. And, as the overground por- 

 tion 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 con- 

 taining a growing Dracwna two and a half 

 feet in height. The worm was left undis- 

 turbed 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 in- 

 soluble constituents being rendered soluble. 

 The author's conclusion was that, inasmuch 

 as he could discover no injury done to the 

 roots of the Dracama, the worm had fed on 

 the remains of plants in the earth, utilizing 

 and decomposing them thoroughly. 



Drowning - Accidents. The advantages 

 of " paddling " aud " 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 pad- 

 dling and treading require no previous in- 

 struction, and in the great majority of cases 

 would save life. In swimming, the mouth 



