Decembek 26, 1890.] 



SCIENCE. 



363 



dropped Professor Mayor's name from the litlepage, although ac- 

 knowledging his indebtedness to that gentleman's book. The dis- 

 tinctive features of the work as now presented consist in its 

 " building-up a boy's knowledge of Greek upon the foundation of 

 his knowledge of English and Latin,"' and in the fact that " no 

 Greek words have been used in the earlier part of the book except 

 such as have connections either in English or Latin." 



— Among the recent publications received from the United 

 States Coast and Geodetic Survey OiBce is " Appendix No. 8, Re- 

 port for 1888.(90 pp. sketch), entitled Geodesy. Geographical 

 Positions in the State of Connecticut. Prepared for publication by 

 Charles A. Schott, assistant." This collection of geographical po- 

 sitions, and of geodetic data re.^ulting, is made in continuation of 

 the scheme of publishing the results in those States where the 

 field-work of the triangulation is substantially completed, and 

 where the triangulation could be made to rest on the standard 

 ■data of the survey. 



— An interesting paper by Professor von Hofmann, upon the 

 dissociation of carbon dioxide gas into carbon monoxide and oxy- 

 gen by means of the electric spark, is referred to in Nature of 

 Dec. 4. Dalton and Henry long ago showed that carbon dioxide, 

 althouj^h formed by exploding a mixture of two volumes of car- 

 bon monoxide with one volume of oxygen by the passage of an 

 electric spark, is again partially decomposed into carbon monox- 

 ide and oxygen by the continued passage of the spark. This dis- 

 sociation, however, is very slow, and usually incomplete. Hof- 

 mann and Buff, in the course of their well-known work upon 

 gaseous re-actions, further showed that " the electric spark passes 

 through carbon dioxide with a violet glow, producing at first a 

 rapid increase in the volume, which, however, becomes less and 

 less marked until at the expiration of about half an hour the sep- 

 arated carbon monoxide and oxygen reoombine with a sudden ex- 

 plosion, the re-formed carbon dioxide at once commencing to be 



again dissociated." Deville and Berthelot afterwards investigated 

 the same phenomena, and also found that the re-action was never 

 complete, proceeding only until about 28 or 29 per cent of the 

 carbon dioxide was decomposed, but they never observed any ex- 

 plosive recombination as described by Hofmann and Buff. Pro- 

 fessor Hofmann has therefore determined the exact conditions under 

 which the explosive recombination occurs. It certainly appears 

 somewhat remarkable that the same spark can effect both disso- 

 ciation and recombination; yet such, within the limits described 

 in the memoir, is an actual fact. The first essential point to be 

 observed is the length of path of the spark. The most suitable 

 distance apart of the platinum terminals appears to be between 

 two and a half and three millimetres, and Professor Hofmann 

 advises the use of adjustable terminals rather than the ordinary 

 platinum wires fused into the side of the eudiometer. A Leyden 

 jar in the circuit renders the occurrence of periodical explosions 

 more certain. The spark should also pass at about a quarter the 

 height of the gas column, instead of, as usual, near the top. The 

 current itself, moreover, should not be too strong: that from two 

 Bunsen cells and only a moderate sized Ruhmkorfl coil is quite 

 sufficient, and yields the best results. It is also preferable to use 

 a volume of carbon dioxide, previously dried over oil of vitriol, 

 not exceeding ten cubic centimetres at a pressure of 650-700 mil- 

 limetres : eight cubic centimetres give excellent results. Under 

 these conditions, the first explosion usually occurs in from fifteen 

 to twenty minutes, and sometimes earlier. The flame commences 

 in the neighborhood of the spark, and then perceptibly spreads 

 through the whole length of the gas column. It is colored blue 

 in the first explosion, and green in the succeeding ones, owing to 

 the volatilization of a little mercury vapor. The second and suc- 

 ceeding explor;ions occur after shorter intervals than the first. 

 This experiment is certainly one of the most interesting in all the 

 range of dissociation phenomena; and full details, with drawings 

 of the apparatus, are given by Professor Hofmann in his memoir. 



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