August 28, 1884] 



NATURE 



vortices, 1 whether cored or coreless, does not seem to imply the 

 liability of translational or impulsive energies of the individual 

 vortices becoming lost in energy of smaller and smaller 

 vibrations. 



As a step towards Kinetic theory of matter it is certainly most 

 interesting to remark that in the quasi-elasticity, elasticity look- 

 ing like that of an india-rubber band, which we see in a vibrating 

 smoke-ring launched from an elliptic aperture, or in two smoke- 

 rings which were circular, but which have become deformed 

 from circularity by mutual collision, we have in reality a virtual 

 elasticity in matter devoid of elasticity, and even devoid of 

 rigidity, the virtual elasticity being due to motion, and generated 

 by the generation of motion. 



SECTION B 

 chemical science 

 Opening Address by Prof. Sir Henry Enfield Roscoe, 

 Ph.D., LL.D., F.R.S., F.C.S., President of the 

 Section 



With the death of Berzelius in 1848 ended a well-marked epoch 

 in the history of our science ; with that of Dumas — and, alas ! 

 that of Wurtz also — in 18S4 closes a second. It may not perhaps 

 be unprofitable on the present occasion to glance at some few 

 points in the general progress which chemistry has made during 

 this period, and thus to contrast the position of the science in the 

 " sturm und drang" year of 1848, with that in the present, 

 perhaps quieter, period. 



The differences between what may probably be termed the 

 Berzelian era and that with which the name of Dumas will for 

 ever be associated show themselves in many ways, but in none 

 more markedly than by the distinct views entertained as to the 

 nature of a chemical compound. 



According to the older notions, the properties of compounds 

 are essentially governed by a qualitative nature of their con- 

 stituent atoms, which were supposed to be so arranged as to form 

 a binary system. Under the new ideas, on the other hand, it is 

 mainly the number and arrangement of the atoms within the 

 molecule, which regulate the characteristics of the compound 

 which is to be looked on not as built up of two constituent groups 

 of atoms, but as forming one group. 



Amongst those who successfully worked to secure this impor- 

 tant change of view on a fundamental question of chemical 

 theory, the name of Dumas himself must first be mentioned, and, 

 following upon him, the great chemical twin-brethren Laurent 

 and Gerhardt, who, using both the arguments of test-tube and of 

 pen in opposition to the prevailing views, gradually succeeded, 

 though scarcely during the lifetime of the first, in convincing 

 chemists that the condition of things could hardly be a healthy 

 one when chemistry was truly defined " as the science of bodies 

 which do not exist." For Berzelius, adhering to his preconceived 

 notions, had been forced by the pressure of new discovery into 

 the adoption of formula; which gradually became more and more 

 complicated, and led to more and more doubtful hypotheses, 

 until his followers at last could barely succeed in building up the 

 original radical from its numerous supposed component parts. 

 Such a state of things naturally brought about its own cure, 

 and the unitary formulje of Gerhardt began to be generally 

 adopted. 



It was not, however, merely as an expression of the nature of 

 the single chemical compound that this change was beneficial, 

 but, more particularly, because it laid open the general analogies 

 of similarly constituted compounds, and placed fact as the touch- 

 stone by which the constitution of these allied bodies should be 

 ascertained. Indeed, Gerhardt, in 1S52, gave evidence of the 

 truth of this in his well-known theory of type, according to 

 which, organic compounds of ascertained constitution can be 

 arranged under the four types of hydrogen, hydrochloric acid, 

 water, and ammonia, and of which it is, perhaps, not too much 

 to say that it has, more than any other of its time, contributed 

 to the clearer understanding of the relations existing amongst 

 chemical compounds. 



Another striking difference of view between the chemistry of 

 the Berzelian era and that of what we sometimes term the modern 

 epoch is illustrated by the so-called substitution theory. Dumas, 



1 See papers by the author "On Vortex Motion," Traits. R. S- E., April 

 1867, and " Vortex Statics," Proc. R. S. E., December 1875 ; also a paper by 

 J. J. Thomson, B.A., " On the Vibrations of a Vortex Ring," Trans. R. S., 

 December 1881, and his valuable book on "Vortex Motion." 



to whom we owe this theory, showed that chlorine can take the 

 place of hydrogen in many compounds, and that the resulting 

 body possesses characters similar to the original. Berzelius 

 opposed this view, insisting that the essential differences between 

 these two elements rendered the idea of a substitution impossible, 

 and notwithstanding the powerful advocacy of Liebig, and the 

 discovery by Melsens of reverse substitutions (that is, the re- 

 formation of the original compound from its substitution-product), 

 Berzelius remained to the end unconvinced, and that which was 

 in reality a confirmation of his own theory of compound radicals, 

 which, as Liebig says, "illumined many a dark chapter in 

 organic chemistry," was looked upon by him as an error of the 

 deepest dye. This inability of many minds to see in the 

 discoveries of others confirmation of their own views is not 

 uncommon ; thus Dalton, we may remember, could never bring 

 himself to admit the truth of Gay-Lussac's laws of gaseous 

 volume-combination, although, as Berzelius very truly says, 

 if we write atom for volume and consider the substance in 

 the solid state in place of the state of gas, the discovery of 

 Gay-Lussac is seen to be one of the most powerful arguments 

 in favour of Dalton's hypothesis. 



But there is another change of view, dating from the com- 

 mencement of the Dumas epoch, which has exerted an influence 

 equal, if not superior, to those already named on the progress 

 of our science. The relative weights of the ultimate particles, 

 to use Dalton's own words, which up to this time had been 

 generally adopted by chemists, were the equivalent weights of 

 Dalton and Wollaston, representing, in the case of oxygen and 

 hydrogen, the proportions in which these elements combine, viz. 

 as 8 to I. The great Swedish chemist at this time stood almost 

 alone in supporting another hypothesis ; for, founding his argu- 

 ment on the simple laws of volume-combination enunciated by 

 Gay-Lussac, he asserted that the true atomic weights are to be 

 represented by the relations existing between equal volumes of 

 the two gases, viz. as 16 to I. Still these views found no 

 favour in the eyes of chemists until Gerhardt, in 1843, proposed 

 to double the equivalent weights of oxygen, sulphur, and carbon, 

 and then the opposition which this suggestion met with was 

 most intense, Berzelius himself not even deigning to mention it 

 in his annual account of the progress of the science, thus proving 

 the truth of his own words : " That to hold an opinion habitually 

 often leads to such an absolute conviction of its truth that its 

 weak points are unregarded, and all proofs against it ignored." 

 Nor were these views generally adopted by chemists until 

 Cannizaro, in 1858, placed the whole subject on its present firm 

 basis by clearly distinguishing between equivalent and molecular 

 weights, showing how the atomic weights of the constituent 

 elements are derived from the molecular weights of their volatile 

 compounds based upon the law of Avogadro and Ampere, or 

 where, as is the case with many metals, no compounds of known 

 vapour-density exist, how the same result may be ascertained by 

 the help of the specific heat of the element itself. Remarkable 

 as it may appear, it is nevertheless true that it is in the country 

 of their birth that Gei'hardt's atomic weights and the consequent 

 atomic nomenclature have met with most opposition, so much 50 

 that within a year or two of the present time there was not 

 a single course of lectures delivered in Paris in which these were 

 used. 



The theory of organic radicals, developed by Liebig so long 

 ago as 1S34, received numerous experimental confirmations 

 in succeeding years. Bunsen's classical research on cacodyl, 

 proving the possibility of the existence of metallo-organic radicals 

 capable of playing the part of a metal, and the isolation of the 

 hydrocarbon ethyl by Frankland in 1849, laid what the sup- 

 porters of the theory deemed the final stone in the structure. 



The fusion of the radical and type theories, chiefly effected by 

 the discovery in 1849 of the compound ammonias by Wurtz, 

 brings us to the dawn of modern chemistry. Henceforward 

 organic compounds were seen to be capable of comparison 

 with simple inorganic bodies and hydrogen not only capable of 

 replacement by chlorine, or by a metal, but by an organic group 

 or radical. 



To this period my memory takes me back. Liebig at Giessen, 

 Wohler in Gottingen, Bunsen in Marburg, Dumas, Wurtz, and 

 Laurent and Gerhardt in Paris, were the active spirits in Conti- 

 nental chemistry. In our own country, Graham, whose memor- 

 able researches on the phosphates had enabled Liebig to found 

 his theory of polybasic acids, was working and lecturing at 

 University College, London ; and Williamson, imbued with the 

 new doctrines and views of the twin French chemists, had just 



