The late Dr. Thomas Thomson. 257 



instances of superacid and subacid salts, and that he had intended to 

 pursue the subject so as to learn the cause of so regular a relation ; but 

 that such a pursuit was rendered superfluous by the appearance of Dal- 

 ton's theory, as explained and illustrated by Thomson. He shows also 

 that the bicarbonate of soda loses one-half its carbonic acid by exposure 

 to a red heat — that the potash in supersulphate of potash is united to 

 twice as much acid as the same quantity of potash in the neutral sulphate, 

 and that potash unites with three different quantities of oxalic acid, 

 which bear to each other the relation of 1, 2, and 4. Dr. Thomson 

 always said, that in the absence of Dalton, WoUaston would have been, 

 very soon, the discoverer of the atomic theory. 



These facts gradually drew the attention of chemists to Mr. Dalton 's 

 views. Sir Humphry Davy, however, and others of our most eminent 

 chemists, were hostile to them. In the autumn of 1807, Dr. Thomson 

 had a long conversation with Mr. Davy at the Royal Institution, 

 during which he attempted in vain to convince him that there was 

 any truth in the new hypothesis. A few days after, he dined with 

 him at the Royal Society Club at the Crown and Anchor in the 

 Strand. Dr. WoUaston was also present. After dinner every mem- 

 ber left the tavern, except Dr. "WoUaston, Mr. Davy, and himself, who 

 all remained behind, and sat an hour and a-half conversing upon the 

 atomic theory. WoUaston and Thomson tried to convince Davy of the 

 inaccuracy of his opinions ; but he went away more prejudiced than ever. 

 Soon after, Davy met Mr. Davies Gilbert, the President of the Royal 

 Society, and exhibited to him the atomic theory in so ridiculous a light, 

 as to make Mr. Gilbert call afterwards on Dr. WoUaston, to learn, pro- 

 bably, what could have induced a man of his sagacity and caution to adopt 

 such opinions. Dr. WoUaston begged of Mr. Gilbert to sit down and 

 listen to a few facts which he would state to him. He then went over 

 the principal facts, at the time known, respecting the salts in which the 

 proportion of one of the constituents increases in a regular ratio ; and the 

 relations also which Dalton had found carbon to bear to hydrogen in 

 defiant gas and carburetted hydrogen. Mr. Gilbert went away a convert 

 to the truth of the atomic theory, and had soon the merit of convincing 

 Sir Humphry Davy, who ever after was a strenuous supporter of it. 



This incident is related in Dr. Thomson's " History of Chemistry," 

 published in 1831 — one of the most delightful books that can be read by 

 a zealous chemist. It is full of biography and anecdote connected with 

 chemistry and chemists. The lives of most of the moderns are taken, 

 with little alteration, from the Annals of Philosophy, where bo had 

 first published them, and the series is there completed, not of course 

 with the same originality, but with prodigious industry and great dis- 

 crimination, accompanied also with interesting additions and criticisms of 

 his own. The book was published in tlie modest form of a contribution 

 in two volumes to the " National Library." It has never appeared in 

 any other form, and if Messrs. Colburn and Bentley could induce Dr. 



