286 



NA TURE 



[September 2, lyog 



on the geometric side in discussing the relation of form to 

 structure/ 



The discovery of trimethylene by Freund and the subse- 

 quent introduction of synthetical methods of preparing 

 polymethylenes by W. H. Perkin, jun., mark the onset 

 • of a new era, opening out as they did the possibility of 

 understanding the structure of camphor and the terpenes 

 and other constituents of the volatile oils from plants. 



Chemist after chemist had attempted in vain to solve 

 the riddle presented by camphor. Suddenly, in a moment 

 of inspiration, a satisfactory solution of the problem was 

 offered by Bredt. The acceptance of the bridged ring, the 

 special feature of the Bredt formula of camphor, marks the 

 introduction of a new moment into organic chemistry. 



The recognition of similar rings in several hydrocarbons 

 of the terpene class, mainly in consequence of the masterly 

 work of von Baeyer, has contributed in no slight degree to 

 an understanding of these compounds : nevertheless, much 

 remains to be learnt and there are many and serious 

 difficulties to be overcome before we shall be in a position 

 to appreciate the genetic relationship of all the substances 

 included in the group. When the account of the work is 

 written it will form one of the most striking and fascinat- 

 ing chapters in the history of our science. 



■\mong the many names of those who have contributed 

 to its development the first to be mentioned is that of 

 Wallach, to whose unwearied efforts, continued during a 

 long series of years, so much is owing. The synthetic 

 work carried out with brilliant success in recent years by 

 W. H. Perkin may also be referred to as of extraordinarv 

 promise but of well-nigh inconceivable difficulty. 



Before leaving this chapter, reference should be made to 

 the almost protean character of camphor, as disclosed by 

 the work of inquirers such as Kipping, Pope, Forster. 

 Lapworth and Lowry ; no other substance has lent itself 

 to use in quite so many directions and with such fruitful 

 results. Special mention may be made of the demonstra- 

 tion which Pope has given, with the aid of the camphor- 

 sulphonic acids, that nitrogen, sulphur, selenium and tin 

 give rise to optically active substances in all respects 

 analogous to those furnished by carbon. The success with 

 which Kipping 's arduous labours have been crowned is 

 also very noteworthy, taking into account the many diffi- 

 culties he has overcome in preparing optically active silicon 

 compounds. The extension of the Pasteur-van 't Hoff 

 theory of asymmetry inferentially to all elements which 

 are at least quadrivalent, now accomplished, is of super- 

 lative importance. 



Lowry's refined observations on the conditions which 

 determine the interconversion of isodynamic forms of some 

 of the camphor- derivatives may also be cited as of special 

 value as a contribution to the studv of metamerism and 

 the conditions which determine chemical change generallv. 



\ot the least interesting feature of camphor is the light 

 thrown by its behaviour on the influence which oxygen 

 exercises as an attractive element and on the part which 



1 The time is now approaching when it will be possible to extend the 

 study of benzenoid compounds beyond the formal and superficial stage ; 

 hitherto we have been content to develop the methods of preparing such 

 substances and to determine their number and their distinctive properties. 

 Ever>-thing has to be learnt as to the exact character of the changes which 

 attend their formation from the parent substance benzene and as to the exact 

 nature of their inter-relationship. The impression produced by benzene, in 

 my mind, is that of an eminently plastic system capable of responding to 

 every slight change that may be impressed upon it. Nothing is more re- 

 markable than the difference between benzene and its homologues, so obvious 

 in the extraordinary increase in activity which attends the introdtiction of 

 hydrocarbon radicles in place of one or more hydrogen .itonis. But such 

 plasticity is not characteristic of benzene only : if the properties of benzene- 

 sulphonic acid be contrasted with those of the various substituted benzene- 

 sulphonic acids, it is clear that ever>- \'ariation meets with some response from 

 the sulphonic group ; what is still more remarkable, if the hydrogen in the 

 hydroxylic group in the phenolsulphonic acids be displaced by other radicles, 

 not only does the oxygen atom to which the radicle is attached seem to 

 respond to the change but the benzenoid system and the still more distant 

 sulphonic system are also affected. It is well known that the physical con- 

 stants are all v.iriables in the case of benzenoid compoimds. Perhaps the 

 most remarkable confirmation of the view here advanced, however, is that 

 afforded by the conclusion arrived at by Barlow and Pope that in the case of 

 benzene derivatives, although the spheres of influence of the carbon and hy- 

 drogen atoms are relatively the same as in the parent compound, the spatial 

 arrangement of the component spheres of atomic influence remaining practi- 

 cally unchanged, nevertheless the actual volumes of the spheres of influence 

 of both carbon and hydrogen alter proportionally to the alteration in mole- 

 cular volume. Thus they maintain that in the case of the conversion of 

 benzene (molecular volume 77*4) into tetrabromobenzene (molecular volume 

 130'2), the volumes of the spheres of influence of both carbon and hydrogen 

 - expand in the ratio of 77*4 : i3o"2. Such a conclusion is very noteworthy. 



NO. 2079, VOL. Si] 



spatial configuration may play in determining directions of 

 change. It is clear that, whatever the agent, the attack is 

 always delivered from the oxygen centre and that the 

 direction in which the attack becomes effective depends on 

 the position which the agent can take up relatively to the 

 various sections of the molecule.' 



It must be confessed that our efforts to penetrate behind 

 the veil in the case of the higher carbohydrates — starch 

 and cellulose in particular — have not been rewarded with 

 success. 



Moreover, though much has been done of late years to 

 unravel the nature of the vegeto-alkaloids, substances such 

 as quinine are still only partially deciphered and not one 

 of the more complex alkaloids has been produced synthetic- 

 ally. In view of the .fact that quinine is still the one 

 effective and practically safe anti-malarial medicine, the 

 disclosure of its constitution is much to be desired. The 

 isolation of adrenaline from the suprarenal capsule and the 

 discovery that this alkaloid — which is an extraordinarily 

 active substance physiologically — plays a most important 

 part in controlling vital processes is of supreme interest. 

 Other glands — the pituitary gland, for example — appear t6 

 contain peculiar active substances, which are of particular 

 consequence in regulating animal functions. The discovery 

 of such substances affords clear proof that life is largely 

 dependent on what may be termed chemical control. 



In addition to indigo, the simpler yellow and red natural 

 colouring-matters have now been thoroughly examined, but 

 this class of substance still affords abundant opportunity to 

 investigators. Kostanecki's comprehensive studies of the 

 xanthone group may be referred to as of particular value. 



Attention ma\' be directed here to the investigation of 

 brazilin and hasmatoxylin by W. H. Perkin and his vari- 

 ous co-workers, not merely as being full of interest and 

 importance as a contribution to our knowledge of the 

 relation between colour and structure and as a brilliant 

 example of technical skill but because of the illustration 

 it affords of the extreme intricacy of such inquiries and of 

 the vast amount of Labour they entail. The general public 

 probably has not the slightest conception of the difficulties 

 which attend such research work and of its costliness. 



As an investigator of vegetable colouring-matters, no 

 one has been more assiduous or has displayed greater skill 

 of late years than .\. G. Perkin. His recent refined inves- 

 tigation of the colour-yielding constituents of the indigo 

 plant is of exceptional value at the present time, although 

 it is to be feared that it comes too late to save the situation 

 in India. The work of the brothers Perkin, it may be 

 pointed out, is of exceptional interest on the human side 

 as well as from the scientific standpoint, as their enthu- 

 siasm and wonderful manipulative skill afford a striking 

 and noteworthy example of hereditary genius. 



Two substances of commanding interest which have long 

 resisted attack — the red colouring-matter of the blood and 

 leaf-green — are at last going the way of all things chemical, 

 as the secret of their nature is being wrung from them. In 

 Willstatter's skilful hands chlorophyll is proving to be by 

 no means the fugitive material it was supposed to be ; the 

 complexity of the problem it offers, however, seems to be 

 far beyond anything that could have been anticipated ; so 

 much greater will be the interest attaching to the final 

 solution. The discovery that green chlorophyll is a mag- 

 nesium salt is of special importance, as the first clear 

 indication of the manner in which magnesium salts are of 

 service to plants. 



Apart from the special interest which attaches to the 

 investigation of vegetable colouring-matters on account of 

 their being coloured substances, such inquiries are of value 

 as furnishing material for the discussion of the metabolic 

 activity of plants. - 



1 Cf. Chem. Soc. Trans. 



2 But a note of sadness pervades the story. The efli'ect of learning^ to 

 understand Nature always appears to be that we at once brush her aside 

 when we have wrested from her the secrets which she has so long preserved 

 inviolate. No sooner did we learn the nature of the madder colouring- 

 matters than we proceeded to prepare them arlitically — thus putting an 

 end to the cultivation of a valuable crop. Indigo is meeting with a like 

 fate, a catastrophe which might well have been avoided had scientific 

 assistance been called in at the proper time. Not content with making 

 natural colouring-matters, we set to work to outrival the rainbow in our labora- 

 tories and the feminine world is decked with every variety of colour in conse- 

 quence, although unfortunately our blends too often lack the beauty of those 

 of truly natural origin, which rarely, if ever, off'end the eye. We congratulate 

 ourselves on our cleverness in thus imitating Nature but no idea of thrift 



