TRANSACTIONS OF SECTION B. 661 



the active spirits in continental chemistry. In our own country, Graham, whose 

 memorahle researches on the phosphates had enabled Lieb'ig 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 been appointed to the chair of practical chemistry in the same college, 

 vacant by the death of poor Fownes. At the same time, Hofmann, in whom 

 Liebig found a spirit as enthusiastic in the cause of scientific progress as his own, 

 bringing to England a good share of the Giessen fire, founded the most successful 

 school of chemistry which this country has yet seen. 



At the Edinburgh meeting of this Association in 1850, Williamson read a 

 paper on ' Results of a Research on iEtherification,' which included not only a 

 satisfactory solution of an interesting and hitherto unexplained problem, but was 

 destined to exert a most important influence on the development of our theoretical 

 views. For he proved, contrary to the then prevailing ideas, that ether contains 

 twice as much carbon as alcohol, and that it is not formed from the latter by a 

 mere separation of the elements of water, but by an exchange of hydrogen for 

 ethyl, and this fact being in accordance with Avogadro's law of molecular volumes, 

 could only be represented by regarding the molecule of water as containing two 

 atoms of hydrogen to one of oxygen, one of the former being replaced by one of 

 ethyl to form alcohol, and the two of hydrogen by two of ethyl to form ether. 

 Then Williamson introduced the type of water (subsequently adopted by Gerhardt) 

 into organic chemistry, and extended our views of the analogies between alcohols 

 and acids, by pointing out that these latter are also referable to the water-type, 

 predicting that bodies bearing the same relations to the ordinary acids as the ethers 

 do to the alcohols must exist, a prediction shortly afterwards (1852) verified by 

 Gerhardfs discovery of the anhydrides. Other results followed in rapid succession, 

 all tending to knit together the framework of modern theoretical chemistry. Of 

 these the most important was the adoption of condensed types, of compounds 

 ■constructed on the type of two and three molecules of water, with which the 

 names of Williamson and Odling are connected, culminating in the researches 

 of Brodie on the higher alcohols, of Berthelot on glycerine, and of Wurtz on the 

 <libasic alcohols or glycols ; whilst, in another direction, the researches of Hofmann 

 •on the compound amines and amides opened out an entirely new field, showing 

 that either a part or the whole of the hydrogen in ammonia can be replaced by 

 other elements or elementary groups without the type losing its characteristic 

 properties. 



Again, in 1852, we note the first germs of a theory which was destined to play 

 an all-important part in the progress of the science, viz., the doctrine of valency or 

 atomicity, and to Frankland. it is that we owe this new departure. Singularly 

 -enough, whilst considering the symmetry of construction visible amongst the inor- 

 ganic compounds of nitrogen, phosphorus, arsenic, and antimony, and whilst putting 

 forward the fact that the combining power of the attracting element is always 

 satisfied by the same number of atoms, he does not point out the characteristic 

 tetrad nature of carbon ; and it was not until 1858 that Couper initiated, and 

 Kekule, in the same year, thoroughly established the doctrine of the linking of the 

 tetrad carbon atoms, a doctrine to which, more than to any other, is due the extra- 

 ordinary progress which organic chemistry has made during the last twenty years, 

 a progress so vast, that it is already found impossible for one individual, even 

 though he devote his whole time and energies to the task, to master all the details, 

 or make himself at home with the increasing mass of new facts which the husy 

 workers in this field are daily bringing forth. 



The subject of the valency of the elements is one which, since the year above 

 referred to, has given chemists much food for discussion, as well as opportunity for 

 experimental work. But whether we range ourselves with Kekule', who supports 

 the unalterable character of the valency of each element, or with Frankland, who 

 insists on its variability, it is now clear to most chemists that the hard and fast lines 

 upon which this theory was supposed to stand cannot be held to be secure. For if 

 the progress of investigation has shown that it is impossible in many instances to 

 affix one valency to an element which forms a large number of different compounds, 



