The late Dr. Thomas Thomson. 259 



water, and having exactly sixteen times its density in the state of 

 ga.-s, had an atomic weight of 8. In the same way he gave 14 for azote 

 and for phosphorus, 16 for sulphur, 20 for calcium, 24 for sodium, 28 for 

 iron, 32 for zinc, 36 for chlorine, 40 for potassium ; and thus he obtained 

 not only round numbers as compared with hydrogen, but numbers which 

 when divided by 2, and most of them by 4, were still multiples by even 

 numbers, and without residue, of the weight of hydrogen. 



Thomson was again the first to perceive the truth and the importance 

 of the discovery made by Dr. Prout. He immediately adopted it, and in 

 November, 1818, he published a new table of atomic weights, embodying 

 its principles, and taking advantage of all the improvements that had been 

 made in analysis during the previous five years. 



In the meantime Berzelius, by a long course of the most persevering 

 exertion, had obtained experimental results of great exactness and great 

 value, from an immense number of bodies. Many of them were published 

 in 1 813, and others followed. When Thomson published his illustrations of 

 the doctrine of Prout, Berzelius refused to accept it, or to be guided other- 

 wise than by the results of his experiments. The numbers of Berzelius were 

 adopted almost universally on the continent, and partially even in this 

 country. In most instances they diff'ered but slightly from Thomson's num- 

 bers. In others, however, the diiference was considerable, as in the very 

 important case of carbon, where it was nearly 2 per cent. It was not 

 till 1840, that any chemist of note joined Thomson in the defence of 

 Prout's doctrine. During these twenty-five years, he maintained his 

 principles and the correctness of his numbers almost single-handed, for, 

 as in the case of Dalton, Prout had done a great proportion of his work 

 when he announced his theory. The experiments of Biot and Arago, 

 which guided WoUaston, Thomson, and Prout, gave 75"4 as the atomic 

 weight of carbon, oxygen being 100 ; and Prout, on the theoretical 

 considerations I have mentioned, reduced it to 75, which is equal to 6 on 

 the hydrogen scale. But Berzelius, conjointly with Dulong, had obtained 

 a different experimental result, and, in accordance with it, his number for 

 carbon was 76'438. 



At length, however, in December, 1840, a most important paper was 

 read to the Academy of Sciences, by MM. Dumas and Stag, on the 

 quantity of carbonic acid produced by the burning of carbon. Graphite, 

 after undergoing a process of purification, was taken for one set of 

 experiments, and diamond for another. These substances were burned 

 in a modification of the tube for organic analysis, and the carbonic acid 

 was collected in a Liebig's alkali-apparatus. The details are exceedingly 

 interesting, but I must not repeat them here. Several months were 

 spent on this single experiment, and nearly half-an-ouuce of diamond 

 burned. The results from graphite gave 



For the atom of carbon, 74 982 



And those from diamond gave 75'005 



The mean of the whole being 74 903 



