June io, 1920] 



NATURE 



449 



at the Royal Academy. An exhibition of his 

 sketches held after his death comprised more than 

 a hundred separate pictures. 



Himself probably the most eloquent of scientific 

 exponents since Tyndall, it is interesting- to learn 

 that Thompson fully realised, as has many 

 another, the difficulties pertaining- to the giving 

 of a Royal Institution discourse, where it is not 

 unusual for some few of the audience to know 

 quite as much as, if not more than, the lecturer, 

 while the majority can fully understand but little 

 of what they hear. Of .interest also is the account 

 of the slender beginnings of his library, w-hich 

 his proclivities as a collector and as a learned 

 bibliophile led him to accumulate, until, enriched 

 as it was by many ancient works and a whole host 

 of rare pamphlets, it developed into one of the 

 most complete and valuable existing collections of 

 electrical publications. 



It is satisfactory to know that the skill and 

 labour expended in making this collection will not 

 be thrown away, as the whole library is to be 

 preserved intact at the Institution of Electrical 

 Engineers, where it will form a worthy monument 

 to Thompson's industry and discernment. 



A, A. Campbell Swinton. 



Academic Research and Industrial 

 Application. 



The Chemistry and Technology of the Diaco-Com- 

 pounds. By Dr. J. C, Cain. Second edition. 

 Pp. xii+199. (London: E. Arnold, 1920.) 

 Price 125. 6d. net. 



THE important chapter in organic chemistry 

 which is summarised so admirably by the 

 author of the treatise under review affords a strik- 

 ing illustration of the difficulty of explaining the 

 details of a chemical synthesis to a non-chemical, 

 although scientific, audience. 



The element carbon furnishes the framework 

 or skeleton of all organic compounds, but much of 

 the chemical liveliness appertaining^ to the more 

 reactive of these substances is due to nitrogen, an 

 element endowed with a dual personality. In the 

 free state inert and loath to enter into chemical 

 combination, when combined it becomes extremely 

 active. Everything living that grows contains 

 nitrogen, and this element is also present in all 

 organic explosives and in the physiologically active 

 alkaloids. It is, therefore, not surprising- that the 

 study of organic nitrogenous substances has 

 always had a great fascination for chemists, who 

 have never grown tired of speculating on the 

 molecular structure of these compounds. It was 

 from this academic point of view that about 

 NO, 2641, VOL. 105] 



sixty years ago Prof. Kolbe, of Marburg, 

 set his pupils to work on the action of nitrous 

 acid on various aromatic amines, nitrogenous 

 compounds of the ammonia type derived from the 

 aromatic hydrocarbon, benzene. One of these 

 workers was Johann Peter Griess, who, on treating 

 picramic acid with nitrous acid, discovered the 

 first diazo-compound, so called because its mole- 

 cule contained a very reactive group, Nj, consist- 

 ing- of two atoms of nitrogen or azote. 



Purely as a matter of scientific curiosity and 

 without any thought of possible applications, 

 Griess proceeded to generalise this reaction and 

 succeeded in showing- that the common primary 

 aromatic amines yielded diazo-compounds. These 

 diazo-derivatives, he found, were very reactive 

 compounds, and he tried their action on all pos- 

 sible substances. He was thus led to make a dis- 

 covery of the utmost technical importance, 

 namely, the synthesis of the azo-colouring^ matters. 

 The diazo-reaction itself was discovered in 1858, 

 and Griess obtained the first azo-colour in the 

 years 1861-62. This dye was first manufactured 

 in 1865 by Caro, a German chemist then employed 

 by Messrs, Roberts, Dale, and Co,, of Manchester, 

 The greater part of Griess 's work was carried out 

 in England, first in London in Hofmann's labora- 

 tory, and afterwards while engaged with Messrs. 

 Allsopp, of Burton-on-Trent. 



From those early days to the present time the 

 diazo-reaction has gone on becoming increasingly 

 useful both in technical and in academic chemistry. 

 The azo-colours produced a revolution in the art 

 of dyeing because a large and important group 

 was found to have the valuable property of dye- 

 ing cotton directly without the intervention of a 

 mordant. Other azo-dyes have found useful ap- 

 plication as extremely fast mordant dyes on wool, 

 A third group, the azo-pigments or ingrain dyes, 

 are formed within the textile fibre by impregnating 

 this material successively with the components of 

 the azo-coupling. All students of organic 

 chemistry are familiar with the Sandmeyer and 

 Gattermann reactions, by means of which diazo- 

 compounds become synthetic agents useful in elu- 

 cidating the constitution of aromatic or benzenoid 

 derivatives. The diazo-reaction has been of 

 service in the production of synthetic drugs, 

 notably those of the salvarsan group. It 

 was employed during the war in the manu- 

 facture of sternutatory materials for chemical war- 

 fare. These synthetic developments are all duly 

 noted in Dr. Cain's treatise, which includes many 

 references to original literature. To the student 

 of historical chemistry not the least interesting 

 chapters will be those on the theories of the con- 

 stitution of diazo-compounds. This discussion 



