1818.] the Atoms of Chemical Bodies. 339 



chemical bodies in the second volume of the Annals of Philo- 

 sophy, the subject has since that time been investigated with so 

 much skill and perseverance by Dr. Wollaston, Professor Berze- 

 lius, and several other chemists, that improvements have been 

 made in almost every individual number. 1 conceive, therefore, 

 that it will be interesting to chemists if I lay before them an 

 epitome of the present state of the subject. This I shall do by 

 giving a new table of the weights of the atoms of different bodies 

 such as they have been established by the most accurate experi- 

 ments hitherto made. I am far from flattering myself that the 

 numbers which I shall give are all accurate ; on the contrary, I 

 have not the least doubt that many of them are still erroneous. 

 But they constitute at least a nearer approximation to the truth 

 than the numbers contained in the first table. It is only by 

 successive, and probably very slow approximations, that we can 

 expect to reach the truth at last. Every new step is something 

 gained ; and, therefore, deserving of attention. I am far from 

 being apprehensive of being found fault with by those who 

 understand the nature of chemistry, and the true mode of improv- 

 ing it, for having formerly given numbers for the atoms of bodies 

 founded on the best data which I could procure at the time, and 

 for abandoning these numbers for others furnished by more 

 accurate experiments. We may expect, now that accuracy is 

 the great object of chemical experimenters, that more and more 

 precise results will be obtained as we proceed. Many, of 

 course, of the numbers which I now give will be to be abandoned 

 hereafter, and new numbers substituted, founded on experiments 

 approaching nearer to absolute accuracy. Meantime we must 

 be satisfied with the best facts which the science can furnish. 

 I am even of opinion that it has a very material tendency to 

 advance the science to lay before chemists the present state of 

 our knowledge, and the value of the data upon which our con- 

 clusions are founded. 



Weight of an atom. 



1 Oxygen , 1-000 



2 Chlorine 4-500 * 



3 Iodine 15-625t 



4 Hydrogen 0- 125 a 



* The weight of an atom of hydrogen is cjerived from the 

 composition of water. It has been established, that water is 



Thi-. number depends upon the specific gravity of chlorine gas. Gay-Lussae 

 and Thetuird found it 2-47. I think Dr. Pront'n reasons for considering it as 2-5 

 are aatisfai tin . Davy has shown that protoxide of chlorine: is a compound of two 

 volumes f chlorine and one volume of oxygen. Now if we consider it as a com- 

 pound of one atom chlorine + one atom oxygeu, it is obvious that an atom of 

 chlorine will weigh 4 5. 



Tlii, is the number obtained by d'ay-Lussac from the combination of iodine 

 and zinc, whicii he found a compound of 100 iodine + 26-52 zinc. Now 26-59 : 

 100 :: 4*1*5 : 15-625. I have very slightly modified Cay-I.ussac's numbers to make 

 the atom of iodine a multiple of 125. 



v 2 



