LECTURE IV.] HISTORY OF CHEMISTRY. 55 



tained confirmation of the law. The law is to this effect : If 

 two substances, A and B, form several compounds, of which 

 the compositions are all calculated with respect to the same 

 quantity of A, then the quantities of B combined with this, 

 stand to each other in a simple ratio. 20 Dalton sought in the 

 atomic theory, an explanation of this law, which was simply an 

 expression of the observed facts. 



According to the atomic theory, chemical compounds are 

 formed by the arrangement, in juxtaposition, of atoms of the 

 elements, these latter being incapable of undergoing any further 

 decomposition. With regard to this Dalton says : 21 " Chemi- 

 cal analysis and synthesis go no farther than to the separation 

 of particles one from another, and to their reunion. No new 

 creation or destruction of matter is within the reach of chemi- 

 cal agency." By the fact that Dalton assigns a definite unalter- 

 able weight to the atom of every element, and admits the 

 possibility of the combination of several atoms, his theory is 

 brought into harmony with experiment, and becomes, indeed, 

 a necessary consequence of it. According to the number of 

 atoms which enter into combination, the resulting atom may 

 belong to a different order. 



The atoms of elements are simple atoms, or atoms of the 

 first order. 



When i atom of an element A combines with i atom of an 

 element B^ i atom of the second order is produced. 



When 2 atoms of an element A combine with i atom of an 

 element B, i atom of the third order is produced. 



When i atom of an element A combines with 2 atoms of 

 an element B, i atom of the third order is produced. 



When i atom of an element A combines with 3 atoms of an 

 element B, i atom of the fourth order is produced. 



When 3 atoms of an element A combine with i atom of an 

 element B, i atom of the fourth order is produced, etc. 



20 It appears that Dalton never stated the law in this general form. 

 Compare Memoirs of John Dalton, by W. Henry, 79 et seq. 21 New 

 System. I, 212 ; A.C.R. 2, 29. 



