260 The late Dr. Thomas Thomson. 



The experimenters purposely kept themselves ignorant of the weight of the 

 diamond they had employed, until the results were calculated. On one 

 occasion they concluded that 708 milligrammes had been burned, when 

 in reality 717 had been weighed to them. They examined the tube which 

 had contained the diamond, and found there the deficiency— equal to 9 

 milligrammes — in fragments of Brazilian topaz. These experiments were 

 repeated the following year by MM. Erdraann and Marchand. They 

 obtained a result nearly similar, viz. 75,087 for the atom of carbon. 

 The French as well as the German chemists concluded that 75 was the 

 real number for carbon. 



In 1843, M. Dumas made known his adherence to the atomic weights 

 of three more of the elements on Prout's list, viz. hydrogen 0'125, azote 

 1"75, and calcium 2-50. Erdmann and Marchand again corroborated his 

 results for hydrogen and calcium, and detei mined anew the number for 

 mercury to be 12'5, and for sulphur 2'0, oxygen being l-QO. Svan- 

 berg and Norlin found the number for iron to be exceedingly near 

 to 3-5, a result which was confirmed by Berzelius himself. Marignac 

 found, for azote, the number 1'7525, and Anderson 1"744 from his 

 experiments on the nitrate of lead ; close approximations on either side of 

 1"75. It must be admitted, however, that Thomson's numbers for chlorine, 

 potassium, sodium, and a few others of the elements still want confirmation. 

 There seems little doubt, then, (and these experimenters incline to the 

 opinion,) that the doctrine of multiples of hydrogen is a law of nature, and 

 that the more exact we become in our analyses, tlie more shall we ap- 

 proach to it in our results. These are the precise numbers which Prout 

 originally determined, and Thomson for twenty-five years maintained, 

 against much opposition ; and seldom do ingenuity, sagacity, and persever- 

 ance meet with so successful and triumphant a conclusion. I remember 

 having had the chance to announce to Dr. Thomson one of these sub- 

 stances, I forget which, as having dropped into his list. I need not tell 

 his friends that no expression of triumph or of gratification escaped him. 

 He took the result as a matter of course, and was confident, that for other 

 numbers also, it was only a question of time. 



To give an account of Dr. Thomson's own contributions to Nicholson's 

 Journal, to the Philosophical Transactions, to the Annals of Philosophy, 

 to the Records of Science, and to the Proceedings of our own Society, 

 would be to take in review his merits as an investigator more fully than 

 is consistent with my present plan. I will only say that they have their 

 excellences and they have their wants. Other men have observed more 

 of the hidden characters of the substances on which they worked ; and, 

 considering the multitude of experiments Dr. Thomson has conducted, he 

 has certainly made known to us comparatively few important new bodies. 



In 1804, in a paper on the oxides of lead, Dr. Thomson first introduced 

 the use of the Greek ordinal numbers to denote the degree of oxidation 

 of a metal. Thus, the protoxide is that in which the metal is united to 

 a minimum of oxygen ; tlic deutoxido has the second degree of oxidation ; 



