CHEMISTRY. (CHEMICAL PHYSICS.) 



149 



since been followed out to full investigation, and 

 an extensive study has been made of the be- 

 havior of various other substances under similar 

 conditions of oxidation and of the resulting prod- 

 ucts. The peculiar advantage of the method with 

 iron consists in the fact that it is often possible 

 to obtain by it products of limited oxidation 

 which can not be prepared in any other way. 

 Hydrogen peroxide is the most efficient oxidizing 

 agent for the purpose, although others may some- 

 times be substituted. The iron which is essen- 

 tial to the process must in all cases be in the fer- 

 rous condition, but its proportion bears little, if 

 any, relation to the yield. In regard to the 

 general nature of the oxidation, it may be as- 

 sumed that the initial result is the replacement 

 of H by OH. The part played by the iron in these 

 changes is still matter for discussion. The au- 

 thor's provisional theory is that the ferrous iron 

 first replaces nonhydroxylic hydrogen, and is 

 subsequently oxidized; and it is remarked that 

 in .the case of every substance found to be sensi- 

 tive to this reaction nonhydroxylic hydrogen is 

 present, associated in almost every case with alco- 

 holic hydroxyl. The author is studying a vari- 

 ety of subjects of typical constitution, with the 

 hope of throwing further light upon the general 

 nature of this oxidation process, and publishes 

 reports of progress concerning tartronic, lactic, 

 glyceric, and malic acids. 



In an account of aqueous solutions of metallic 

 gold obtained by him through reduction of the 

 chloride, Richard Zsigmondy has shown that me- 

 tallic gold can be held in solution in water in 

 different colored conditions. Although the great 

 variety of colors obtained from the colloidal sil- 

 ver of Mr. Carey Lea can not be produced with 

 gold, yet gold solutions are obtained which are 

 deep red, blue, and black, as w r ell as of shades 

 lying between those colors, according to the con- 

 ditions under which the gold is reduced. The 

 blue or violet solutions seem to be the most easily 

 obtained. The red solution is the one princi- 

 pally studied. It is obtained by treating very 

 diluted, boiling hot, and slightly alkaline solu- 

 tions of gold chloride with different reducing 

 agents, such as formic aldehyde, acetic aldehyde, 

 alcohol, and even hydroxylamine. Other colors 

 are, however, liable to be produced by deviations 

 in the process. The very dilute red solution can 

 be evaporated to half its volume without change, 

 but further boiling will cause it to turn to a 

 dark violet color, with precipitation of gold as 

 a black violet powder. The solution can be re- 

 duced to one twentieth of its volume in a few 

 days. Solutions containing 0.12 per cent, of col- 

 loidal gold were obtained, but on further con- 

 centration metallic gold was precipitated. The 

 red-gold solution passes through the closest filter 

 paper without change. It is tasteless. On addi- 

 tion of neutral salts, acids, or fixed alkalies, the 

 beautiful red color turns to blue; the liquid be- 

 comes turbid, gradually losing its color, and in 

 eight or nine hours the gold falls to the bottom 

 as a blue-black powder. Potassium ferrocyanide 

 changes the color to green, and after twenty- 

 eight hours to yellow; but gold is not precipi- 

 tated. The metallic gold in aqueous solution 

 acts like other dissolved colloidal substances 

 when subjected to electrolysis. 



A detailed study of the properties of liquid 

 ammonia has been undertaken by E. C. Frank- 

 lin and C. A. Kraus for the purpose of fol- 

 lowing out the manifest close relation that exists 

 between that solvent and water. Water, the 

 authors observe, occupies an essentially unique 

 position among the known solvents. Its' physical 



properties, such as its capar-ity as a general solvent 

 for salts and its power of electrolytic dissociation, 

 its low molecular elevation constant, its high boil- 

 ing point, and its heat of fusion, heat of volatiliza- 

 tion, critical temperature and critical pressure, 

 specific heat, association constant and dielectric 

 constant, with values so much higher than the 

 corresponding values for other substances, all 

 combine to distinguish it from other solvents and 

 give it a place by itself. As a result of their 

 studies the authors conclude that of all known 

 liquids ammonia most closely approaches water 

 in all those properties which give that substance 

 a conspicuous position among solvents. In its 

 capacity as a general solvent for salts it is sec- 

 ondary to water, but superior to all other sol- 

 vents. It closely approaches w r ater in its power 

 to dissociate electrolytes; some salts conduct 

 electricity even better in ammonia solution than 

 they do in aqueous solution. It plays a part in 

 many compounds analogous to that of water in 

 salts containing water of crystallization. Its heat 

 of volatilization and probably its association con- 

 stant are higher than those of any other liquid 

 with the one exception of water. For a sub- 

 stance of such simple composition its critical 

 temperature and critical pressure, and its boil- 

 ing point at atmospheric pressure, are remark- 

 ably high, as is still conspicuously true of the 

 corresponding constants in the case of water. Its 

 specific heat is quite as great as that of water, 

 while its molecular elevation constant is lower 

 than that of any other substance for which meas- 

 urements have yet been made. Ammonia differs 

 from water in its inability to dissolve the sul- 

 phates and sulphites, the alkaline carbonates, 

 phosphates, oxalates, the hydroxides of the alkali 

 and alkaline-earth metals, and the facility with 

 which it dissolves organic substances. The liquid 

 does not exhibit a maximum density above the 

 freezing point, and the solid ammonia is not spe- 

 cifically lighter than the liquid at its freezing 

 point. 



Major-Gen. J. Waterhouse, of the Royal Photo- 

 graphic Society, assumes, on the basis of Moser's 

 thermographic observations, that metallic silver 

 is sensitive to light. If cut-out masks be laid 

 upon the surface of silver leaf or foil, silvered 

 glass, or on a daguerreotype plate, and exposed 

 to the sun's rays, a visible image ultimately be- 

 comes apparent on the metallic surface. The 

 effect may, however, be got in a very much 

 shorter space of time if the partly exposed metal 

 be subjected to mercury vapor or developed by 

 immersion in an acid solution of a ferrous salt 

 mixed with nitrate of silver. Clear images, hardly 

 as yet to be called pictures, can thus be obtained 

 of a permanent character, so that it may be 

 possible to work the daguerreotype process with- 

 out iodizing the plate. In fact, the photographic; 

 phenomena of the invisible developable image, the 

 visible image, reversal, and the effect of pressure 

 marks can all be illustrated on the plain silver 

 surface. Copper seems to be sensitive in the 

 same way. 



M. Becquerel has discovered that such sub- 

 stances as develop phosphorescence under the 

 action of the ultra-violet rays are rendered lu- 

 minous by the radiations of radium, while those 

 which develop that property under the red rays 

 are not so affected, and he remarks upon other 

 analyses between the ultra-violet rays and those 

 emitted by radium. 



New Substances. The emission of active 

 rays from pitchblende has been found by M. and 

 Mme. Curie not to proceed only from the urani- 

 um contained in the mineral, but from two other 



