CHEMISTRY. 



95 



precipitate depends on the amount of sugar 

 present. If this is very small, the gray or black 

 precipitate forms slowly, and it is necessary to 

 allow it to stand for some time (ten or fifteen 

 minutes). This reduction occurs in the cold, 

 after standing quietly for twenty-four or forty- 

 eight hours. The bismuth solution will remain 

 unaltered, and can be diluted to any degree 

 without the precipitation of the bismuth. 

 . New Test for Gallic Acid. Mr. Dudley also 

 proposes the folloVing new test for gallic acid : 

 Prepare a solution of ammonium picrate by 

 adding to a dilute aqueous solution of picric 

 acid an excess of ammonium hydrate. Add a 

 few drops of this reagent to an aqueous solution 

 of gallic acid, and there is produced, at first, a 

 red color, which, in a few seconds, becomes a 

 beautiful green, the depth of color depending 

 on the amount of gallic acid present. Pyrogal- 

 lic and tannic acids produce, at first, a reddish 

 color, but no further material change takes 

 place with them. 



Gallium in American Blendes. Mr. H. B. 

 Cornwall, of Princeton College, has made ex- 

 aminations of American blendes for gallium. 

 Of two European blendes and several Ameri- 

 can ores submitted to the spectroscope, the 

 compact grayish blende from Friedensville, 

 Pennsylvania, showed the gallium line about 

 as plainly as a European specimen from San- 

 tander, which is classed as among the blendes 

 richest in gallium, while a crystallized, rather 

 dark, yellowish-brown specimen from Phcenix- 

 ville, Pennsylvania, showed it more distinctly 

 still. Of other American blendes submitted 

 to examination, those from Joplin, Missouri, 

 Warren, New Hampshire, and Ellenville, New 

 York, gave reason to believe that they contain 

 gallium. According to the studies of Lecoq de 

 Boisbaudran, the alloys formed by heating gal- 

 lium with aluminum remain brilliant, and do 

 not sensibly attract oxygen from the air during 

 their formation. After cooling, they are brit- 

 tle and but slightly coherent. They decompose 

 water with elevation of temperature, evolution 

 of hydrogen, and the formation of a chocolate- 

 brown powder, which ultimately becomes white 

 flocks of alumina, almost the whole of the gal- 

 lium being set free in globules apparently free 

 from aluminum. The slow evolution of hydro- 

 gen by a solid alloy is considerably quickened 

 by contact with a globule of liquid gallium, 

 owing to electric action. Suffused gallium dis- 

 solves aluminum, forming very brilliant, liquid, 

 or pasty alloys, which decompose water with 

 great energy. Ordinarily the decomposition is 

 spontaneous, but sometimes a globule of alloy 

 is inert when thrown into water, while another 

 fragment of the same mass is immediately active, 

 and even renders the first so upon contact with 

 it. On touching the liquid alloy with a frag- 

 ment of solid gallium, crystals appear which 

 are pure gallium, and which do not act on 

 water. After their removal, the alloy is less 

 active, but, if the whole is remelted by the 

 haat of the hand, the alloy regains its activity. 



Variations in the Spectra of Vapors and 

 Gases under Pressure. G. Ciamician has com- 

 municated to the Academy of Sciences of Vi- 

 enna the results of a number of experiments 

 which he has made on the influence of press- 

 ure and temperature on the spectra of gases 

 and vapors. The experiments of Wullner had 

 already shown that with hydrogen, oxygen, 

 and nitrogen, the spectral lines of the second 

 order grow broader with higher pressure, and 

 that this is accompanied with a continuously 

 illuminated background. The phenomenon, 

 however, presents, even in the three perma- 

 nently gaseous elements, very great differ- 

 ences. While the lines in the spectrum of 

 hydrogen become easily broader, even under 

 moderate pressure, those of the spectrum of 

 nitrogen do not expand. M. Ciamician's pur- 

 pose was to institute a comparative investiga- 

 tion, extending to as many elements as possi- 

 ble, for the sake of finding a law, and perhaps 

 an explanation, for the phenomena. The spec- 

 tra of the three halogens, chlorine, iodine, and 

 bromine, at high pressures, exhibit in each case 

 the same peculiarities. The lines have the ap- 

 pearance of merging into each other, and, with- 

 out showing an expansion into bands, they 

 become occasionally somewhat broader. A 

 steadily luminous background is seen, which 

 becomes brighter when the pressure is in- 

 creased, and which is often more intense than 

 the lines themselves. The latter circumstance 

 is frequently seen in the case of iodine, where 

 the continuous spectrum finally covers all the 

 rest; while with chlorine and bromine single 

 lines are always distinguishable from the con- 

 tinuous surrounding light. The appearance is 

 remarked of certain lines in the red field in 

 chlorine and bromine which always preserve 

 their precision and delicacy. Very interesting 

 changes are exhibited in the intensity of the 

 spectral lines under different pressures. It is 

 difficult to ascertain the homology of the lines 

 if the spectra of rarefied vapors in Geissler 

 tubes are employed, for the lines can only be 

 compared in groups, and frequently present in 

 each of the three elements such differences of 

 intensity as to leave in doubt the existence of 

 a homology. The apparent differences arise 

 in reality out of the variation of intensity and 

 of the number of the lines with the pressure. 

 Spectra exhibiting the perfect homology of the 

 lines can always be produced by appropriate 

 changes in the density of the gas or vapor. 

 The spectrum of sulphur exhibits no change 

 under increased pressure. The lines maintain 

 their perfect sharpness, and a continuously illu- 

 minated background appears in the red field. 

 Phosphorus and arsenic give no reaction, and 

 do not show even the continuous spectrum. 

 Arsenic gives at a moderate pressure, and 

 without the interposition of the Ley den jar, 

 a spectrum of the first order, which is almost 

 continuous ; and, with increase of pressure and 

 interposition of the jar, it gives to the spec- 

 trum of lines the spectrum of the second order. 



