66 



NATURE 



[November 17, 1892 



gation of the bromine addition products of angelic and tiglic 

 acids, and was successful in showing that the two products were 

 essentially different, exhibiting properties indeed so dissimilar 

 that their identity was entirely out of the question. Although 

 their similar constitution was indicated by melting-points differing 

 by only one or two degrees, yet it was found that the crystals of 

 the dibromide of angelic acid immediately reacted with water with 

 production of a colourless oil, whilst the dibromide of tiglic 

 acid remained unchanged in contact with water ; moreover, the 

 two compounds upon decomposition of their sodium salts, yielded 

 two mono-brom-pseudo-butylenes, which differed essentially in 

 their capability of reacting with alcoholic potash. 



In the year 1890, however, Prof. Fittig, of Strassburg, who 

 had previously investigated the subject in conjunction with Herr 

 Pagenstecher, and had obtained identical bromine addition pro- 

 ducts from the two acids, published a paper in the Annalen in 

 which he sought to show that the results of Herr Piickert were 

 incorrect, and that the two substances were identical. Prof. 

 Fittig has since requested Prof. Wislicenus to withdraw the work 

 or substantiate it, and further charges Prof. Wislicenus with see- 

 ing facts through the veil of his theory. Unfortunately Prof. 

 "Wislicenus has been unable hitherto to meet the attack owing 

 to domestic loss and serious illness, but at last he is able to pub- 

 lish the results of a really classical piece of work which he has 

 carried through himself, and which not only demonstrates the 

 truth of Herr Piickert's conclusions, but places the results beyond 

 all criticism, and shows the singular cause of Prof. Fittig's in- 

 ability to repeat them. It is indeed remarkable, but neverthe- 

 less true, that the fate of the theory of geometrical isomerism 

 has actually been trembling in the balance owing to the different 

 situation of the draught cupboards in the Leipzig and Strassburg 

 laboratories. In the former laboratory they are placed between 

 the windows, and in deep shadow ; in the Strassburg laboratory 

 they are against the windows, and are consequently brightly 

 illuminated in daylight. Now Prof. Wislicenus shows that the 

 dibromide of angelic acid is only formed in the absence of 

 bright light, ra;/5 of daylight intensity being absolutely fatal to 

 its forviation. Hence Prof. Fittig only obtained the relatively 

 more stable dibromide of tiglic acid, which in a good light is 

 yielded by both angelic and tiglic acids. As the case is so re- 

 markable, it may perhaps not be uninteresting to give a brief 

 summary of the work of Prof. Wislicenus. 



During the course of other researches concerning geo- 

 metrical isomers, it was found that in order to obtain addi- 

 tion-products in which no internal re-arrangement of atoms had 

 occurred, it was necessary to observe three conditions. One 

 must operate at the lowest possible temperature, exclude light 

 as much as possible, and take care that the halogen to be added 

 is always present in tolerably large excess. When these three 

 conditions are observed, the two respective and distinct bromine 

 addition-products of angelic and tiglic acids are always obtained. 

 They are probably represented by the formulae — 

 CH, Br H H Br CH3 



\1/ \!/ 



C C 



i t 



CH3 Br COOH CH3 BrCOOH 



Dibromide of 

 angelic acid. 



Dibromide of 

 tiglic acid. 



The operation of preparation is best conducted as follows : 

 — A quantity of bromine, at least half as much again as is re- 

 quired by theory, and dissolved in three times its weight of 

 carbon bisulphide, is placed in a flask surrounded by iced 

 water. The flask is fitted with a triply bored caoutchouc 

 stopper, through one hole of which is inserted a thermometer, 

 through a second an exit tube furnished with a calcium chloride 

 drying tube, and through the third the end of a burette con- 

 taining a solution of pure angelic or tiglic acid in five times its 

 weight of carbon bisulphide. The draught cupboard is darkened 

 as much as possible and then the acid solution is slowly allowed 

 to run into the flask. After the expiration of a few hours the 

 formation of the brominated compound i^ complete, and the 

 carbon bisulphide may be evaporated away in a rapid stream of 

 dry air. 



The difference between the two compounds is apparent even 

 at this early stage, for the tiglic compound commences to 

 crystallize long beiore the removal of all the carbon bisulphide, 

 and soon forms a snow-white mass of crystals. On the contrary, 



NO. 1203, VOL. 47] 



the angelic dibromide shows no sign of crystallization, remain- 

 ing as an oil for some time after the removal of all the carbon 

 bisulphide. Eventually it crystallizes to a hard yellowish mass. 

 The only solvent from which it was found practicable to re- 

 crystallize the angelic dibromide was the pentane fraction of 

 petroleum ether boiling at 33"-39°. 



The melting-point of pure angelic dibromide is 86 "5-87. That 

 of tiglic dibromide is 87 -5-88. The two substances behave quite 

 differently upon resolidification. The former congeals to a 

 transparent resinous mass, whilst the latter forms an opaque 

 solid. 



The most striking difference is apparent in their respective 

 behaviour towards water. The dibromide of tiglic acid is only 

 slightly soluble in water, and dissolves unchanged, crystallizing 

 out again upon evaporation. The dibromide of angelic acid, how- 

 ever, instantly combines with the equivalent of one molecule of 

 water, to form a curious unstable liquid, an oil of high refractive 

 power, which is somewhat soluble in excess of water, and is 

 again deposited upon evaporation. This liquid compound is 

 also formed when the dibromide is exposed to moist air, while the 

 dibromide of tiglic acid is not changed in a moist atmosphere. 

 In dry air the angelic liquid compound again dissociates 

 into the dibromide and water vapour. In fact the dibromide of 

 angelic acid would appear to act as an excellent indicator of the 

 hygroscopic state of the atmosphere. 



The two dibromides show a further difference in solubility, 

 the angelic compound being far more readily soluble in all the 

 solvents experimented with. 



Finally the crystals of the two compounds, although both 

 belonging to the triclinic system, are absolutely unlike. From 

 measuremenis made by Dr. Fock, they are shown to exhibit 

 different forms, entirely different angles, and different disposition 

 of optic axes. 



From the above description it will be quite evident that the 

 two compounds are certainly not identical. 



In conclusion, Prof. Wislicenus gives the results of attempts 

 to obtain the dibromide of angelic acid in bright sunshine in the 

 open air, then when working in front of a window, and ^ain 

 when the experiment was periormed upon a table in the centre of 

 the laboratory. In the first case, instead of the angelic com- 

 pound, 92*8 per cent, of the dibromide of tiglic acid was ob- 

 tained, in the second case 89-6, and in the third case 887 per 

 cent. These results render it perfectly clear why Prof. F'ttig 

 could not obtain the angelic compound in his experiments, and 

 they also show how it is possible for two chemists, both working 

 with a desire to ascertain the truth, occasionally to obtain results 

 apparently at complete variance with each other. 



A. E. TUTTON. 



C 



MARINE LABORATORIES IN THE UNITED 

 STATES.^ 



NLY in comparatively recent times has the tremendous 

 importance of the bearing of the invertebrates upon the 

 general questions of biology been appreciated. We have seen 

 ihat some work was done upon these animals at an early date, 

 when the minds of workers were not much troubled by theoret- 

 ical considerations, but the study of the adult forms is sn small 

 a part of a real understanding of these animals that it was 

 unsatisfactory work, and never became popular among investi- 

 gators until embr) ological methods had been introduced. 



Dr. Brooks has remarked that "nearly every one of the great 

 generalizations of morphology is based upon the study of marine 

 animals, and most of the problems which are now awaiting a 

 solution must be answered in the same way.'"^ We find the 

 reason for this in the fact that the biology of the present day is 

 a study of vital phenomena and of natural laws governing living 

 things. The importance of the invertebrates depends, there- 

 fore, upon the fact that in them life exists under simplified con- 

 ditions, affoiding opportunities for the study of questions for 

 which higher forms are, with our present knowledge, too 

 complex. 



As the study of invertebrates has extended, it has become 

 more and more desirable to have more favourable conditions for 

 this work, more abundant facilities for collecting and oppor- 



I Reprinted from " Biological Teaching in the Colleges of the United 

 States," by John P. Campbell, Pro'essor of Biology in the University of 

 C/eorgia ; is-^ued by the U.S. Buieau of Education. 



-Johns Hopkins University Circulars, vol. vi., p. 37. 



