326 



NA TURE 



{Feb. 6, 1890 



Messrs. Gauthier-Villars (Paris) have recently added 

 three new works to their already large list of photographic treat- 

 ises. One is the " Manuel de Phototypie," by M. Bonnet, giving 

 full details of the various processes for the rapid reproduction of 

 photographs, such as is now demanded for many purposes. The 

 formulae are stated very clearly, and the apparatus required is 

 sufficiently illustrated by diagrams. The treatise is thoroughly 

 practical, and will be very valuable to all interested in the subject, 

 whether as amateurs or for trade purposes. The second^ — -"Temps 

 de Pose " — is by M. Pluvinel, and deals with the difficult question 

 of the time of exposure. It is shown that what is generally 

 regarded as a rule-of-thumb process can be reduced to a scientific 

 one. The various functions of the duration of the exposure are 

 first considered mathematically, and it is then shown how the 

 results of the investigations are to be applied practically, the 

 method being illustrated by worked- out examples. To simplify 

 matters, tables are given showing the different elements, such as 

 coefficient of brightness, for all ordinary photographic subjects. 

 The treatise is chiefly interesting as a scientific contribution, as 

 few photographers will care to take the trouble of working out 

 the time of exposure, now that they have found that good work 

 can be done by judgment alone. The third book is in two 

 volumes, and treats of the various "film " processes (" Precedes 

 Pelliculaires," by George Balagny). It claims to give a full 

 account of all that has been said and done in connection with 

 the subject since the introduction of photography, and as far as 

 we can judge, this claim is fully justified. Every detail of the 

 subject is considered in a very practical manner. One of the 

 most interesting applications of flexible films mentioned is the 

 registration of flash signals in " optical telegraphy." 



The " Year-book of Photography " (Piper and Castle) for 1890 

 fully bears out the good reputation gained by its predecessors. In 

 addition to the information relating to the various photographic 

 societies, there are several articles on the advances in photographic 

 processes which have been made during the past year, and other 

 useful notes. One of the most interesting articles is that by the 

 editor on photography in natural colours, from which we learn 

 that " processes of practical value, to achieve the end, are likely 

 to be discovered by the exercise of ability and perseverance." 

 The only important omission we notice is a record of the 

 remarkable achievements in astronomical photography. The 

 volume contains a portrait and short biographical notice of 

 Edmond Becquerel. The whole forms an invaluable book of 

 reference to all photographic matters, with the exception 

 referred to. 



Messrs. George Bell and Sons have published "The 

 School Calendar and Hand-book of Examinations, Scholarships, 

 and Exhibitions, 1890." This is the fourth year of issue, and 

 great pains have been taken, as in former years, to secure that 

 the information brought together shall be full and trustworthy. 

 A preface is contributed by Mr. F. Storr. 



The sixteenth part of Cassell's " New Popular Educator " has 

 been issued. It includes a map of Australasia. 



The Proceedings of the International Zoological Congress, 

 held in Paris last summer, will be ready for distribution in a 

 fortnight. 



A NEW and very simple method of synthesizing indigo has 

 been discovered by Dr. Flimm, of Darmstadt {Ber. deut. chem. 

 Ges., No. I, 1890, p. 57). In studying the action of caustic 

 alkalies upon the monobromine derivative of acetanilide, 

 CfiHg.NH.CO.CHjBr, a solid melting at 131° '5, it was found 

 that when this substance was fused with caustic potash a product 

 was obtained which at once gave an indigo blue colour on the 

 addition of water, and quite a considerable quantity of a blue 

 solid resembling indigo separated out. The best mode of carrying 

 out the operation is described by Dr. Flimm as follows : — The 



monobromacetanilide is carefully mixed with dry caustic potash in 

 a mortar, and the mixture introduced into a retort and heated 

 rapidly until a homogeneous reddish-brown melt is obtained 

 This is subsequently dissolved in water, and a little ammonia 

 or ammonium chloride solution added, when the liquid im- 

 mediately becomes coloured green, which colour rapidly changes 

 into a dark blue, and in a short time the blue colouring matter 

 is for the most part deposited upon the bottom of the vessel in 

 which the operation is performed. The fused mass may also 

 conveniently be dissolved in dilute hydrochloric acid, and a little 

 ferric chloride added, when the formation of indigo takes 

 place immediately. The collected blue colouring matter may 

 be readily obtained pure by washing first with dilute hydrochloric 

 acid and afterwards with alcohol. That this blue substance was 

 really common indigo was proved by the fact that it yielded 

 several of the most characteristic reactions of indigotin, such as 

 solubility in aniline, paraffin, and chloroform, its sublimation, 

 and the formation of sulphonic acids, which gave similar changes 

 of colour with nitric acid to those of indigotin. The final proof 

 was afforded by its reduction to indigo white and re -oxidation to 

 indigo blue by exposure to air. Moreover, the absorption 

 spectrum of the colouring matter was found to be identical with 

 the well-known absorption spectrum of indigo. Hence there 

 can be no doubt that indigo is really formed by this very simple 

 process. The chemical changes occurring in the reaction are con- 

 sidered by Dr. Flimm to be the following :— Indigo blue is not 

 produced directly, but 'first, as a condensation product of the 



monobromacetanilide, indoxyl is formed, C^Hj; />CH, 



^\ 



COH^" 



C6H,< 



more probably a pseudo-indoxyl of the isomeric constitution 

 /NH. 



yCH^- This intermediate substance then passes over 

 'CO^ 



/NH. /NH. 



by oxidation into indigo, CgH^ ^C=:C<^ pCgH4, 



\CO/ ^CQ/ 



two molecules each losing two atoms of hydrogen by oxidation, 

 and then condensing to form indigo. It was not found possible 

 to isolate the intermediate pseudo-indoxyl, owing to its extreme 

 instability ; indeed, the all-important point to be observed in the 

 practical carrying out of the synthesis by this method is that the 

 fusion must be performed quickly and the temperature raised 

 rapidly to a considerable height, the whole process occupying 

 only a few minutes. The yield of pure indigo under the con- 

 ditions yet investigated is not very large, amounting to about 

 four per cent, of the weight of the original anilide. 



The additions to the Zoological Society's Gardens during the 

 past week include thirteen Cuning's Octodons {Octodon cuniiigi) 

 from Chili, presented by Mr. W. H. Newman ; five Common 

 Dormice {Muscardimis avellanarius), British, presented by Mr. 

 Florance Wyndham ; a Large Hill-Mynah (6^rafz</(7 intermedia) 

 from India, deposited; a Dingo {Canis dingo), born in the 

 Gardens. 



OUR ASTRONOMICAL COLUMN. 

 Objects for the Spectroscope. 

 Sidereal Time at Greenwich at 10 p.m. on February 6 = yh. 

 7m. 56s. 



