SPECTRUM ANALYSIS 867 



to give free access of air. If a rancid odour is exhaled, and the mass grows green, 

 the process goes on well ; but if it grows black, it must be more freely exposed to the 

 air. As soon as all the surface is covered with green mouldiness, which usually 

 happens in eight or ten days, the cover is removed, and the matter is placed in the 

 sunshine for several days. When it has become as hard as a stone, it is cut into 

 small fragments, thrown into an earthen vessel, and covered with the 250 pounds of 

 water having the salt dissolved in it. The whole is stirred together, and the height 

 at which the water stands is noted. The vessel being placed in the sun, its contents 

 are stirred up every morning and evening ; and a cover is applied at night to keep it 

 warm and to exclude rain. The more powerful the sun the sooner the soy will be 

 completed ; but it generally requires two or three of the hottest summer months. As 

 the mass diminishes by evaporation, well-water is added ; and the digestion is con- 

 tinued till the salt-water has dissolved the whole of the flour and the haricots ; after 

 which the vessel is left in the sun for a few days, as the good quality of the soy 

 depends on the completeness of the solution, which is promoted by regular stirring. 

 When it has at length assumed an oily appearance, it is poured into bags, and strained. 

 The clear black liquid is the soy, ready for use. 



SPANISH GRASS. See ESPABTO and PAPER. 



SPAR, HEAVY or PONDEROUS. Sulphate of baryta. See BARYTA. 



SPARRY XROIf ORE, or SPATHIC IRON. (Syn. Chalybite, Sideritc, 

 Siderose, Brown Spar, &c.) Spathose iron ore has been largely worked on the 

 Brendon Hills, in Somersetshire, and . it is also found on Exmoor, and in Perran- 

 zabuloe, and at the iron mines on the north coast of Cornwall. It also occurs at 

 Weardale in Durham. See IRON. 



SPECIFIC GRAVITY designates the relative weight of different bodies under 

 the same bulk: thus a cubic foot of water weighs 1,000 ounces avoirdupois; a 

 cubic foot of coal, 1,350; a cubic foot of cast iron, 7,280; a cubic foot of silver, 

 10,400 ; and a cubic foot of pure gold, 19,200 : numbers which represent the 

 specific gravities of the respective substances, compared with -water = 1,000. See 

 GRAVITY, SPECIFIC. 



SPECTRUM, Solar or Prismatic. If a pencil of solar light is admitted through 

 a small hole, into a dark room, and allowed to fall upon the edge of a prism, a beauti- 

 fully-coloured flame-like image is formed upon the opposite wall ; the order of colours 

 being red, orange, yellow, green, blue, indigo, and violet, the red being the least re- 

 frangible ray, and the violet the most so of the ordinary visible rays. Careful examina- 

 tion proves the yellow ray to be the most luminous ; the red ray the most calorific ray ; 

 and the violet to possess the most energetic chemical power. Heat-rays, invisible under 

 ordinary conditions exist below the red band ; some of them having peculiar powers, 

 are known as the parathermic rays ; and chemical rays extend, with much power, far 

 beyond the violet end of the visible spectrum. Luminous rays are also rendered visible 

 at the most refrangible end of the spectrum by throwing the spectral image into a solu- 

 tion of sulphate of quinine, or on a piece of uranium glass, and some other substances ; 

 these are called the fluorescent rays. With this brief description of the Newtonian 

 spectrum, as it is often called, (Sir Isaac Newton, being the first who investigated its 

 striking phenomena) our readers must be satisfied. The practical applications of our 

 knowledge form the subject of the next article. 



SPECTRUM ANALYSIS. Dr. Wollaston was the first who observed the ex- 

 istence of non-luminous spaces or dark lines in the solar spectrum. Dr. Ritchie proved 

 that these lines were dependent on absorption, and showed how they could be in- 

 creased in visible numbers by artificial means. Fraunhofer, however, was the first to 

 make a full investigation of them, and to publish a map of them ; hence they have been 

 generally called Fraunhofer's Lines. 



These lines are of so fixed a character in relation to the coloured bands of the 

 spectrum, that if it is desired to indicate with great precision any special rays of the 

 spectrum, they are referred to by letters or numbers. The position the lines occupy 

 have been determined by a careful examination of the map of Fraunhofer, and the 

 very complete delineation of those lines published in the ' Philosophical Transactions ' 

 for 1859, by Sir David Brewster and Dr. Gladstone. Fraunhofer laid down on his 

 map 354 lines, but Sir David Brewster says : ' In the delineations which I have exe- 

 cuted, the spectrum is divided into more than 2,000 visible and easily recognised por- 

 tions, separated from each other by lines more or less marked.' 



The origin of these dark lines, spaces in which there is no light, can scarcely be 

 said to be yet satisfactorily resolved. Fraunhofer, and others following him, thought 

 that the light emitted from the photosphere was, from the first, deficient in those rays, 

 or that thej' were lost, either by absorption in passing through the solar atmosphere, 

 or obtained possibly in passing through that of the earth. Angstrom, who also dis- 

 covered many bright lines in the spectra from artificial lights, advanced some highly 



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