at the Royal Institution, 1908-1916 737 



In 1826 he made another discovery of cardinal importance to the 

 same industry, that of sulphonaphthalic acid — naphthalenemlphonic 

 acid we now term it. Though chronicled by Bence Jones in his 



1740, it is stated that ' fossile carbons ' on distillation yield a little water and 

 * a sharply tasting spirit,' which must have been benzol." 



This disingenu )us statement does not appear in the previous edition. Those 

 who are acquainted with the behaviour of coal when distilled are well aware 

 that the " spirituous " product is a very complex mixture from which it is by 

 no means an easy matter to separate benzene. The quotations given obviously 

 do not contain the faintest approach to an anticipation of Faraday's discovery. 

 In his paper read before the Royal Society on June 16, 1825, he describes how 

 he isolated benzene, by cooling the liquid with ice and salt, as a crystalline 

 solid, of definite melting point ; the liquefied substance boiled at a definite tem- 

 perature. He determined the density of the liquid and also of its vapour ; finally 

 he made an exact analysis of the substance and deduced the composition of 

 the hydrocarbon correctly, the formula he gave to it being that now used after 

 translation into terms of the pre.?ent-day molecular theory. He made a full 

 chemical examination of the hydrocarbon and he nitrated it, though he did 

 not isolate nitrobenzene ; he even sulphonated it. Taking into account his 

 training and the state of knowledge at the time, it is one of the most remark- 

 able pieces of early work in organic chemistry with which we are acquainted. 

 Having worked with a material practically identical with that used by Faraday, 

 I can appreciate the extraordinary skill he displayed in making his discovery-. 

 It may be mentioned that the gaseous hydrocarbon noticed by Faraday 

 accompanying the benzene is not, as is often stated, the hydrocarbon butylene, 

 C4H8 but, in all probability, crotonylene C^Hg (cf . Cham. Soc. Journ., ] 886, p. 74). 



Another German, Prof. Otto N. Witt, in a communication to the Berlin 

 Chemical Society made shortly before his death (Ber., 1915, p. 743), by 

 implication rather seeks also to detract from the originality of Faraday's 

 work with naphthalene by attributing to Brande the discovery that when the 

 hydrocarbon is dissolved in sulphuric acid it gives " a soluble substance of acid 

 nature." This statement is not in accordance with what Brande says. 



The account of his work appeared in the Quarterly Journal of Science 

 (1820, pp. 21, 181) imder the title "On a Substance produced during the 

 Distillation of Coal Tar." He was not even aware, at the time, what particular 

 compound he was dealing with. He speaks of it only as a white crystalling 

 substance and states that : — 



" In sulphuric acid, when aided by heat, it dissolves in considerable abund- 

 ance, forming a deep violet-coloured solution which bears diluting with water 

 without decomposition." 



Faraday, early in his memoir (Phil. Trans., 1826, p. 140), refers to Brande's 

 work and reproduces this statement. But, at the outset, after speaking of his 

 previous work on benzene referred to above, he goes on to state that he was 

 led to study the action of sulphuric acid on "analogous" bodies — naphthalene 

 among others — because he " had occasion to notice the peculiar action exerted 

 on certain of these compounds by sulphuric acid. Daring my attempts to 

 ascertain more minutely the general nature of this action, I was led to suspect 

 the occasional combination of the hydrocarbonaceous matter with the acid 

 and even its entrance into the constitution of the salt which the acid afterwards 

 formed with bases." 



Obviously, he was in possession already of a perfect method of reasoning. 

 For its time, the work is altogether remarkable on account of its complete- 

 ness. He recognized the existence of " a peculiar compound of sulphuric acid 

 with the elements of the naphthalene which possesses acid properties." He 



Vol. XXI. (No. 110) 3 c 



