Mtxy I, 1879"! 



NATURE 



cult to see from the drawing what is meant in the arrange- 

 1 ment figured between the washing bottle and the French 

 ' drying tube. There are some traces also of careless 

 printing, which it would be well to rectify in future 

 editions, as in the equation of the action of arseniuretted 

 hydrogen on silver nitrate on p. 373. The title of the 

 book is also somewhat presumptuous; it is styled "A 

 Manual of Practical Chemistry:" the two last words being 

 in large type ; a colon is here introduced and then 

 follows the exact title of the book in smaller type, " The 

 Analysis of Foods and the Detection of Poisons." The 

 work cannot be fairly described as a Manual of Practical 

 Chemistry, and the title should therefore have been 

 restricted to the matter actually contained in the book. 



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, 



[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 otheiiuise to ensure the appearance even of com ■ 

 munieations containing interesting and novel facts. 1 



On the Spectrum of Brorsen's Comet 



With reference to Prof C. A. Young's Note on the Spectrum 

 of Brorsen's Comet, in Nature, vol. xix. p. 559, it may be of 

 interot to mention that observations made at the Royal Ob- 

 servatory, Greenwich, confirm his conclusion as to the coincid- 

 ence of the brightest band in the comet spectrum with the green 

 band of carbon. 



We w ere not able to examine the comet's spectrum till April 

 17, as the Great Equatoreal was in the workmen's hands till that 

 date for alterations required to allow of the more convenient use 

 of the spectroscope. On that evening, and again on April 19, 

 the comet's spectrum was repeatedly compared by Mr. Maunder 

 and myself, with the spectrum of alcohol taken in a vacuum 

 tube. The less refrangible edge of the brii^hlest comet-band 

 coincided as exactly as could be determined with the correspond- 

 ing edge of the green carbon-band at S,2C0, but the comet- 

 hand was very nuch wider, extending two-thirds of the way 

 towards F (i.e., about 2co tenth-metres), and covering the carbon- 

 hand at 5,200 (about 30 tenlh-metres broad) and the two follow- 

 ing fainter bands at 5,100 and 5,020. The comparisons were 

 made on April 17 by the help of an occulting bar, and on April 

 19 "ith Hilger's bright-line micrometer, illuminated by red 

 light. With the latter, readings for the comet- and carbon- 

 bands respectively, agreed within half a tenth-metre. The half 

 prism spectroscope with a dispersion of lo» from A to H (equi- 

 valent to two prisms of 60°) was used on the 13-inch equatoreal. 

 From spectroscopic observations of the carton compound, 

 printed in the volume of Greenwich Observations, 1875, it 

 appears that the bands in the spectrum of alcohol are identical 

 with those in the spectra of olefiant gas, and of carbon oxide 

 and dioxide. 



A second band was seen in the orange of the comet's spectrum 

 approximately coincident with the carbon band at about 5,600. 

 This band was of about one-fourth the brightness of the principal 

 hand. 



The resuhs on April 17 were obtained without a knowledge 

 of Trof. Young's work, and thus afford an independent confir- 

 mation of his conclusion. W. H. M. Christie 



Royal Observatory, Greenwich, April 21 



Blue Flame from Common Salt 



I AM perfectly aware that, as Dr. Gladstone points out in your 

 last issui , I have not proved f ICl to be the origin of the blue 

 flame, but I will give some of my reasons for thinking so. 



In the first place I conclude every one will admit that chlorine 



in some form must be present, since only chlorides produce the 



flame. At one time I thought it was due to dissociated or 



^ atomic chlorine ; that view, however, I discarded in favour of 



the hydrochloric acid theory. 



When AmCl is heated, dissociation occurs, as is well known, 

 NHj and HCl being formed ; the HCl then plays its part in 



producing the blue flame. If calomel be used, it is natural to 

 imagine that the mercury and chlorine are separated, and if the 

 colour is due to HCl, the addition of hydrogen will be necessary 

 before the flame is produced. As a matter of fact I have found 

 that no coloration occurs if the calomel is heated in what I may 

 perhaps be allowed to call the solid part of the Bunsen flame, i.e. 

 where complete combustion takes place, but it is necessary to 

 allow some of the unburnt gas to mingle with its vapour. In 

 practice I adjust the w ire gauze over the burner so that a black 

 spot is seen surrounded by a red hot ring, a little calomel placed 

 on the dark spot volatilises and colours the gas that is btuning 

 above the gauze ; if the gauze is raised so that the dark spot 

 vanishes and all is red hot, the salt volatilises without any 

 coloration ensuing. 



Although I have not been able to see any violet bands when a 

 spark has been taken in HCl, I do not consider that it negatives 

 my theory, since there is a considerable diflisrence between an 

 electric spark and a Bunsen flame, and I now have reason to 

 think that under the influence of the spark the HCl is split up 

 into its components, which will fully account for the absence of 

 violet bands. 1 have likew ise failed to get them from a spark in 

 AmCl. 



A drop of liquid HCl, introduced into a Bunsen flame by the 

 aid of a platinum wire, gives a flash of blue colour, and a lighted 

 taper immersed in a bottle of HCl gas has its flame surrounded 

 by a blue mantle just before it gees out. The colour, to the eye, 

 is identical in both cases to that produced by the volatilisation of 

 a chloride, the peculiar violet tinge showing that it must contain 

 rays of high refrangibility. 



Lastly, if a stream of HCl gas be slowly pasfed into a large 

 Bunsen flame, the colour is produced most vividly, the spectrum 

 showing all the characteristic lines or bands. Here we have the 

 HCl under the same conditions as the chloride ar.d w ith a similar 

 result. 



Dr. Gladstone appears not to have obtained the flame by this 

 method, since he says : " Hydrochlcric acid passed into a flame 

 never gives the violet light." 



This may probably be explained by the fact that if the HCl 

 be passed too rapidly the violet coloration gives place to green, 

 similar to that produced by chlorine alone if the stream of gas 

 be cllovved to slacken, the violet is reproduced, and this may be 

 repeated indefinitely. A. Percy Smith 



Temple Observatory, Rugby, April 26 



Did Flowers Exist during the Carboniferous Epoch? 



According to the position Mr. Wallace has taken in the 

 discussion as to the order of insects to which Breyeria borinensis 

 presumably belongs, everything depends upon the existence or 

 non-existence of transverse reticulation. I re-assert that a regular 

 and thoroughly well-marked transverse reticulation exists over all 

 the wing. 



If Mr. Wallace prefers to believe in the evidence afforded by 

 a photograph in preference to my statement based upon actual 

 examination, and to M. de Borre's words in his description 

 ("Entre toutes ces nervures s'etend un reseau extremement 

 complet de tres-fines nervules allant transversalement d'lme 

 grosse nervure a I'autre "), it is evident that anything I could say 

 would not alter his opinion. 



Further, I utterly fail to comprehend by what process of 

 reasoning he arrives at the conclusion that the photograph " is 

 so beautifully sharp that it brings out the minutest details," 

 when confessedly he has not compared that photograph with the 

 original. 



That the main nervures may be compared with some forms in 

 Lepidoptera and found to agrte to a certain extent is very pos- 

 sible ; it would be singular if it were otherwise, considering the 

 extreme variation in the neuration of Lepidoptera, and the prac- 

 tical certainty that the system of neuration in all orders of insects 

 can be homologised. The presence of dense transverse reticu- 

 lation in a lepidopterous insect would decidedly be an anomaly ; 

 but its absence would not prove that any particular fossil did not 

 belong to the Ephemerida;, for in some recent genera of the 

 latter, such as Oligoneuria, Lachlania, &c., the transverse reticu- 

 lation is so far absent as to be reduced to a few nervules that 

 might be counted on the fingers of one hand. 



Supposing, for the sake of argument, that my assertion may 

 be based upon false premises (and no one is infallible), Breye- 

 ria would probably be relegated to that heterogeneous assemblage 

 of extinct forms of insects possessing densely reticulate wings, to 



