484 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



posed for sixty seconds at a distance of nineteen inches from 

 the light, while screened from its action by ten unequal lay- 

 ers of waxed paper, the first four inches long, covering the 

 whole plate, and each successive layer being one tenth short- 

 er, the last being four tenths of an inch long. The effects 

 were compared by noticing, after development, the number 

 of layers of paper through which the light had acted. Thus 

 it was found that the oxyhydric light penetrated but one 

 layer; the Drummond light, three; that of zinc burned in 

 oxygen, four ; of the magnesium light, five ; of a jet of nitric 

 oxide passed through a flask containing bisulphide of carbon, 

 six; of a jet of nitric oxide in a vessel of burning bisulphide 

 of carbon, six and seven ; of a jet of oxygen in a vessel of 

 bisulphide of carbon, seven ; of a jet of oxygen in a vessel of 

 burning sulphur, eight. The introduction of oxygen into a 

 jet of burning sulphur, as it produced the greatest effect upon 

 the bromide of silver, seems to merit further tests as to its 

 practical value. 19 C, VIIL, 127. 



riEE-PEOOF PAPER AND INK FOR VALUABLE DOCUMENTS, ETC. 



The fire -proof writing-paper prepared, according to an 

 English patent, of one part vegetable fibre, two parts asbes- 

 tus, one tenth of a part borax, and two tenths of a part alum, 

 can also be made of a heavier quality, suitable for binding 

 books and preserving manuscripts, etc. The fire-proof ink 

 may be used for printing as well as Avriting. It is composed 

 of twenty-two drams finely powdered graphite, twelve grains 

 copal varnish, two drams sulphate of iron, and eight drams 

 tincture of gall-nuts and indigo carmine; all well mixed, and 

 boiled in water. Any mineral pigment may be substituted for 

 the graphite to form a colored ink. 9 (7, XIII., 152. 



IMITATION OF JACOBSEN's COPYING-INK PENCILS. 



Imitations of Jacobsen's substitute for ink, in the form of 

 copying-ink pencils, have made their appearance. They con- 

 sist essentially of the same ingredients as the original, name- 

 ly, graphite and aniline color, but are consolidated simply by 

 means of tragacanth or other mucilage, instead of by the pe- 

 culiar process by which the compact, homogeneous mass of 

 the original is formed. The imitation is, therefore, readily 

 distinguished, since it is very porous and brittle, is never 



