240 



NATURE 



[December 21, 191 1 



select the same or similar dyestuffs. It is also a 



desideratum for the merchant or textile manufacturer 

 to be able to ascertain whether the colour of the mate- 

 rials dyod for him is always obtained with the dye- 

 stuffs specified, whether the shade dyed by one firm 

 is or is not a chemical match for that dyed by another, 

 and other similar questions. The analytical chemist 

 is also frequently called upon to determine the actual 

 dyestuff or dyestuffs employed, for example, in the 

 composition of a lakr pii^Miicnt for wall-papers or 

 lithographic printing, (u- to identify the material used 

 for colouring certain food products. 



With the large number of dyestuffs which come 

 into consideration it is obvious that no satisfactory 

 scheme of identification can be based upon individual 

 and empirical reactions, such, for instance, as the 

 changes of colour produced by caustic soda or concen- 

 trated sulphuric acid. Such individual tests can only 

 be employed effectively after the genetic relationships 

 of the dyestuff in question have been ascertained by 

 means of suitable group reagents; and only those 

 chemical properties can be employed as group reactions 

 which depend upon general differences in chemical 

 structure. Another reason why such a principle can 

 alone prove satisfactory is that the scheme adopted 

 must be capable of including and referring to their 

 appropriate groups the new colouring matters which 

 are constantly appearing, the individual reactions of 

 which are unknown. 



In the analytical scheme published by A. G. Green 

 in 1893, which is based in part upon the earlier 

 schemes of Witt and Weingaertner, the chief differ- 

 entiation is effected by the behaviour of the dyestuff 

 upon reduction with zinc dust, and the reaction of its 

 reduction products with air and with chromic acid. 

 Whilst nitro-, nitroso-, and azo-compounds are com- 

 pletely broken down upon reduction, and cannot there- 

 fore be reoxidised, those dyestuffs which may be 

 regarded as having an ort/io-quinonoid structure give 

 leuco-compounds which are readily reoxidised to the 

 original dyestuff by air, and those to which a para- 

 quinonoid structure is attributable give leuco-com- 

 pounds stable to air but reoxidised by chromic acid. 

 Still, a further group are not reducible at all, whilst 

 dyestuffs of the anthracene class are converted into 

 coloured hydro-derivatives. 



In 1905 and 1907, Green, assisted by Yeoman, Jones, 

 Haley, and Stephens, published a very complete 

 scheme for the analysis of dyestuffs upon textile 

 fibres, in which the above principles were employed in 

 conjunction with other group tests. In this scheme 

 sodium hydrosulphite was substituted for zinc dust as 

 the reducing agent, and the colourless potassium per- 

 sulphate for chromic acid, all the reactions being 

 effected upon the fibre instead of in solution. This 

 scheme of analysis is not only applicable to dyed mate- 

 rials, but can also be readily applied to colouring 

 matters in the solid form or when associated with 

 mineral bases, food products, &c., by previously trans- 

 ferring the dyestuff to wool or cotton. 



In the work under review the author claims to have 



produced a perfected scheme of analysis of general 



applicability. In place of employing group reactions 



to differentiate the dyestuffs according to their struc- 



NO. 2199, VOL. 88] 



tura! relationships and dyeing properties, the sy«tei: 

 adopted is largely empirical, being based upon ili 

 exact determination of colour changes effected 1 

 various reagents, the shades obtained being compar- 

 with standard sh;ide cards and the results tabula i.<: 

 bv a system of lettering. Although Green's reduitimi 

 and oxidation tests are also employed as "generi* ' 

 reactions, their indications are interpreted in a strictly 

 formal manner under arbitrary but rigidly fixed con- 

 ditions. This produces the result that the main 

 groups or "genera" frequently contain dy^ 

 stuffs which are entirely unrelated. We find, 

 for instance, azo-colours of the benzopurpurine 

 type classified together with rhodamine (a i 

 colour); phosphine and other acridine colours cl;i 

 with annatto; auramine (a diphenylmethane dcriv 

 tive) in association with primullne (a compound ■ 

 the thiazol class); various alizarine colours in clo-' 

 conjunction with rose Bengal and violamines (pyroii' 

 colours) ; and dyes of the azo-class, triphenylmethan' 

 and natural red woods amongst the azines, oxazin' 

 and thiazines. The author's system also involves t! 

 coordination of dyestuffs of entirely different dyeii 

 properties, irrespective of whether they are "basic . 

 "acid," "substantive," or "mordant" colours. 



The book contains colour reactions of some 1475 

 individual dyestuffs, which are recorded with extreme 

 precision for the selected conditions. Although, how- 

 ever, it has involved much careful labour, the utili 

 of the work has been largely sacrificed to the desire lo 

 obtain an impossible degree of accuracy and through { 

 the unscientific and inconvenient system of diff- r- 

 entiation adopted. Such a rigid system of colour i 

 actions does not take account of the fact that com- 

 mercial dyestuffs usually contain variable impurities 

 or are shaded with small quantities of other colour! t- 

 matters. Furthermore, it may be questioned whet): 

 the exact tint obtained in the tests would not be a! 

 affected by small indeterminate factors, such as t 

 purity of the reagents or the quality of the text; 

 materials used in dyeing. Lastly, the scheme couu; 

 not be applied to mixtures without a complete separa- 

 tion into the constituents, a condition which is seldom 

 possible. .\rthur G. Green. 



MUNICIPAL ENGINEERING. 

 A Manual of Civil Engineering Practice : Specially 

 arranged for the Use of Municipal and County * 

 Engineers. By F. Noel Taylor. Pp. xiiH-8oo. 

 (London: C. Griffin and Co., Ltd., 191 1.) Pr: 

 255. net. 



THIS book has been written to supply the needs 

 of young engineers who propose to devote them- 

 selves to those branches of engineering practice which 

 fall to the lot of the municipal and county engineer, 

 or the borough surveyor; the duties which have to 

 be undertaken by such officials are of a most var: 

 character, and involve a wide range of knowledge ; 

 books of reference are essential to such men, and 

 Mr. Taylor, drawing largely upon his own profes- 

 sional experience, has dealt with the entire field of 

 work covered by the term "municipal civil engineer- 

 ing." 



