34o 



NA TURE 



[August 9, 1883 



present and the preceding reports, that they contain a 

 mass of information on fish and fisheries of a kind which 

 has never been before brought to a focus, and in issuing 

 such a guide to all interested, the United States Govern- 

 ment has set us an example which we ought at once to 

 follow. The volume is published at Washington, and is 

 printed at the Government Printing Office. 



LETTERS TO THE EDITOR 

 [ The Editor does not hold himself responsible for opinions expressed 

 by his correspondents. Neither can he undertake to return, 

 or to correspond with the writers of, rejected manuscripts, 

 No notice is taken of anonymous communications. 

 I The Editor urgently requests correspondents to keep their letters 

 as short as possible. The pressure on his space is so great 

 that it is impossible otherwise to insure the appearance even 

 of communications containing interesting and novel facts.'] 



Cyanogen in Small Induction Sparks in Free Air 



Among the "Notes" inNATURE for July 19 (p. 281), where the 

 products of combustion are given for various illuminants in 

 common or uncommon use, and where coal-gas, oils, and 

 candles have a fearful amount of both water-vapour and car- 

 bonic acid charged against them, the return for electric lights 

 b^th in the arc and incandescent shapes is given a-; o - o for each ; 

 a return which is there considered to show " the great supre- 

 macy of electric lighting over all the other methods of illumina- 

 tion when considered as a matter of health." 



Now this I believe is most happily true of the incandescent 

 electric lights hermetically sealed in their vacuous glass globes ; 

 but who, on second thoughts, would presume to say that it is so 

 with the arc lights, consuming their carbons visibly in the open 

 air? The solid carbon gradually disappears from view, every 

 one allows, and if it has not combined in gaseous condition with 

 the oxygen of the atmosphere, like that of wax candles, it must 

 have mainly combined with the nitrogen, and formed the far 

 more deleterious compound gas, cyanogen, the basis of prussic 

 acid : and that such gas or hydrocyanic acid is produced in the 

 electric arc was set forth by Prof. James Dewar in the Royal 

 Society Proceedings for June 19, 1879. 



Leaving the great arc lights, therefore, to such a master of 

 the subject, chemical, physical, and electrical, as the Jacksonian 

 Professor in the University of Cambridge, I would request to be 

 allowed to mention here a spectroscopic proof, which I have not 

 seen mentioned before, that cyanogen is also formed in every 

 induction electric spark worked under atmospheric pressure. 



In plate I of M. Lecoq de Boisbaudran's admirable "Spectres 

 Lumineux" he gives beautifully engraved views of the spectrum 

 of the induction electric spark first at the positive pole, then at 

 the negative pole with a "mean length " of spark, which was in 

 his case probably about one inch ; its extreme length with his in- 

 duction coil and bichromate battery, in its best condition, being 

 two inches. 



Now the spectrum he gives for the positive pole is neither 

 more nor less than the low temperature spectrum of nitrogen ; 

 that is as we see nitrogen in a gas-vacuum tube, with all its 

 numerous and delicately shaded bands as such, though it is 

 bioxide of nitrogen according to M. Thalen. 



But the spectrum which M. Lecoq de Boisbaudran gives for 

 the negative pole has in addition to the above, and besides the 

 red hydrogen line, a number of other most distinct lines and 

 bands, including one line in the violet, which he dignifies with 

 the letter a, and which is certainly the grandest thing in the 

 whole spectrum. 



In his printed pages I do not find that the celebrated French 

 spectroscopist gives any explanation of the origin of either that 

 line or the other supernumeraries, the hydrogen line excepted. 

 But on turning to my own paper on " Gaseous Spectra " printed in 

 vol. xxx. of the Transactions of the Royal Society, Edinburgh, 

 in 1881, I find on pp. 119 and 122, last column, that almost 

 every one of the lines and bands which I had separated there 

 from the impurities or dissociated elements of the tube's contents 

 and had put down as due to the compound gas "cyanogen" 

 is coincident in place and character with some one or other 

 supernumerary in M. Lecoq de Boisbaudran's spectrum of the 

 negative pole. My spectrum places are indeed very rough, 

 owing to the small amount of dispersion then employed, viz. 

 one simple prism of white flint with a refracting angle of 52° ; 

 but the testimony of the whole is cumulative, and, considering 



Spark at the Negative Pole in the Open Air by M. Lecoq de 

 Boisbaudran, with a rather Wide Slit 



Colour W " ^' ^ ace Inten- Appear- 



Reeion approx. in stty ance Description. 



s Brit. inch, approx. approx. 



Orange 41,300 

 Citron 44,850 



Green 



Green 



/ 48,600 

 l49,3°o 



50, 100 

 5o,Soo 



Narrow band. 



Stronger band with hazy 

 line. 



Group of bands and hazy 

 lines. 



Broad band with stronger 

 edges. 



r-i ( 53,8oo) '* := Larger and strong 



Glaucous J ^; 70Q J 4 SSg the preceding. S 



5 Very thin line. 



er than 



Blue 



Violet 



Violet 

 Violet 



55,200 2 

 59,400 8 



Most powerful line, the 

 « of the spectrum. 



59, 5°° 5 ^c. A. darkening of the nitro- 



gen band. 



900 5 2—31 Broad band, with strong 

 400 5 a^^S terminal bars. 



f 59. 



1 60, 



Cyanogen's Concluded Spectral Lines by C. Piazzi Smyth, with a 

 rather A r arro70 Slit 



Colour W - N ' P1 ? ce Inten- Appear- 



Orange 



/4I.I46 

 1 41,55 



552 



Citron 44,878 

 48,582 



2 fe 

 2 & 



Description. Reference page. 



Cyanogen ? 

 Cyanogen 



111 



Green 



Green 



. 49,350 



49,996 

 50,728 



4 u, 



3 i 



True cyan, group 120 & 121 



Sharp line begins ( 



a band of lines. ( ' 20 



Isolated line. 120 & 122 



** Cyanogen. 



120 



and 122 



l 53,963 3 fe. Not nitrogen nor 

 carbon. 



54-570 



Blue 55,271 



Violet 59,405 



2 J Cyanogen ? 



2 I Cyanogen ? 



(•Grand line, fol- ' 



lowed by a band, f ,, 



characteristic oil I2 0&I22 



Violet i 59.9SS 2-o 



\ 60,356 - 2 



Violet 60,541 ro 



I cyanogen. 



fc. Cyanogen. 



' Cyanogen ? 



Nitrogen ? 



120 & 122 



the totally independent manner in which my results were arrived 

 at, and the certainty with which they were slated on their own 

 merits, perfectly overwhelming. 



Thus — of the line which I now identify with that one which is 



