106 



CHEMISTRY. 



Carey Lea, of Philadelphia, and the results 

 published in the American Journal of Science 

 and Arts. In those metallic salts which suffer 

 reduction under the action of light, the nature 

 of the acid has much to do with the facility of 

 reduction ; thus ferric oxalate and citrate are 

 much more easily reduced than ferric sulphate. 

 Further, the reducibility of a s"alt is, as a rule, 

 influenced by the substances in contact with it : 

 thus silver chloride, when alone, changes rather 

 slowly to violet; more rapidly, and to a deeper 

 violet, when in contact with silver nitrate ; on 

 certain sorts of organic matter being added, 

 the change is still more rapid, and the color 

 produced may be intense black. It is affirmed 

 by .Dr. Hermann Vogel that in the case of 

 silver bromide such contact not only affects its 

 general sensitiveness to light, but also modifies 

 its impressibility to rays of different refrangi- 

 bilities. According to Vogel, this change fol- 

 lows a definite law, viz. : the colored sub- 

 stances, absorbing certain rays, increase the 

 impressibility of the bromide to those rays 

 which they absorb. Thus a colored substance 

 which absorbs the yellow rays and radiates the 

 rest of the spectrum, increases the sensitiveness 

 of silver bromide to the yellow rays. The ex- 

 istence of this law Mr. Lea was unable to 

 verify. Below is an abridged account of his 

 experiments. 



1. Ferric Salts. Strips of paper were first strongly 

 colored with aurine, with aniline blue, and with ani- 

 line green, and then impregnated with ammonia 

 ferric oxalate and exposed, side by side with ordinary 

 white paper similarly impregnated, to a spectrum (an 

 artificial spectrum made by coating strips of glass 

 with suitable transparent pigments). After exposure 

 both papers were plunged into a solution of ferrid- 

 cyanide of potassium, which produced Turn bull? s 

 blue in the reduced portions, the remainder continu- 

 ing white. The result of three experiments was to 

 show the aniline blue to be without influence. The 

 aniline green slightly diminished the impressibility, 

 but not more in one part than in another. The aurine 

 produced this effect more strongly. Neither coloring 

 matter exerted any specific influence on the impressi- 

 bility by any particular portion of the spectrum. 



2. Potassium Bichromate. In contact with aurine 

 this salt showed no change of action in its behavior 

 to white, blue, or violet light, nor in the orange or 

 the red. In the yellow it was less impressed than 

 the bichromate strip of paper without aurine. Papers 

 colored with aniline blue and green acted like the 

 plain bichromate, but were perhaps a trifle less sen- 

 sitive to the whole spectrum. 



3. Potassium Ferrideyanide. Papers colored with 

 aurine, coralline, aniline red, blue, and green, and 

 mauveine, were exposed, the reduction being brought 

 about with ferric ammonia oxalate. All these six 

 colors diminished the impressibility of the ferrid- 

 cyanide throughout the whole range of the spectrum-, 

 and no relation could be traced between the color 

 used and the impression of particular rays. 



4. Uranic Nitrate. The same coloring-matters 

 used. With short exposures to violet and white light 

 only the mauveine appeared to give a slight increase 

 of sensitiveness ; but as the increase extended equally 

 to white and violet, no conclusion could be drawn as 

 to influence on specific rays. The coralline dimin"- 

 iishe'd the general sensitiveness a good 'deal, the aurine 

 nearly destroyed it, and the -three aniline colors 

 diminished it a little. 



5. 'Silver Chloride. 'Here coralline, rosaniline, and 



red litmus-paper, increased the sensitiveness to blue 

 and violet ; mauveine and aniline green were with- 

 out eifect, and aurine diminished sensitiveness to all 

 six. 



6. Silver Iodide. Here a violet-blue aniline color 

 increased the sensitiveness to yellow and green rays ; 

 but also had a similar effect upon the violet. Aniline 

 green increased the sensitiveness to violet, blue, 

 green, and yellow rays, but not to the orange and 

 red (the colors approximating to its own color), while, 

 on the contrary, coralline increased the sensitive- 

 ness to the rays most difl'erent from its own color. 

 Hence no definite law appears. 



1. Silver Bromide. Here colorless substances as 

 well as those possessing color were placed in contact 

 with the salt to be reduced. The result was that 

 none of the many substances used exerted a more 

 discriminating action on the sensitiveness to indi- 

 vidual rays than salicine, a perfectly colorless sub- 

 stance : it rendered the silver bromide as sensitive 

 to the red ray as to the green. The author's conclu- 

 sion is, that " there is no general law connecting the 

 color of a substance with the greater or less sensi- 

 tiveness which it brings to any silver haloid for any 

 particular ray." 



The Centennial of Chemistry. The celebra- 

 tion of the hundredth anniversary of the dis- 

 covery of oxygen gas was one of the notable 

 events of the year 1874. The idea of this cen- 

 tennial originated with Prof. H. C. Bolton, of 

 Columbia College, New York, who, in a com- 

 munication to the American Chemist, enumer- 

 ated the many important discoveries in chem- 

 istry which signalized the year 1YT4, and which 

 mark that period as the starting-point of 

 modern chemical science. The project was 

 favorably received, and, at the suggestion of 

 Prof. Eachel L. Bodley, Northumberland, Pa., 

 where Priestley lived after coming to this coun- 

 try, and where he is buried, was selected as the 

 place of meeting. In answer to the call, nearly 

 one hundred chemists assembled at Northum- 

 berland on July 31st. Dr. C. F. Chandler was 

 chosen president of the meeting, and was con- 

 ducted to the chair by Priestley's grandson, Dr. 

 Joseph Priestley. The more prominent features 

 of this interesting celebration were, an address 

 on the "Life and Labors of Dr. Priestley," by 

 Prof. Henry H. Croft, of University College, To- 

 ronto ; the reading of several of Priestley's let- 

 ters written while residing in this country; an 

 address, "A Century's Progress in Theoretic 

 Chemistry," by Prof. T. Sterry Hunt ; a me- 

 morial tribute at the grave of Priestley, deliv- 

 ered by President Coppee, of Lehigh Univer- 

 sity; a "Keview of the Century's Progress in 

 Industrial Chemistry," by Prof. J. Lawrence 

 Smith, of Louisville, Ky. ; and an address of 

 Prof. Benjamin Silliman, on " American Con- 

 tributions to Chemistry." A visit to the house 

 which Priestley built, and in which he died ; 

 an inspection of his " shed," or laboratory, in 

 which he did his scientific work ; and the ex- 

 hibition of apparatus, manuscripts, and pict- 

 ures, relating to Priestley, contributed in large 

 measure to the interest of the proceedings. 



Composition of the Water of Great Salt 

 Lake. In the Chemical News, H. Bassett 

 gives an analysis of the water of the Great 

 Salt Lake. He finds the total solid residue in 



