LAWS AND THEORIES OF CHEMISTRY. 97 



advocated a theory of atoms. But the views of the ancients were 

 speculative and had no physical basis resting upon experiments, and 

 therefore were of no service to science. It was not until 1804 that a 

 theory or conception of matter was proposed by John Dalton, of 

 England, that had the merits of being capable of being put to tests 

 and from which deductions could be made that lent themselves to ex- 

 perimental verification. Dalton's atomic theory holds that (1) elements 

 arc made up of inconceivably small particles which are indivisible in 

 chemical actions and called atoms (from the Greek dro//oc, uncut, or 

 not yet divided) ; (2) the atoms not only have definite weights, but 

 the atoms of any one element have the same weight, which is differ- 

 ent from the weight of the atoms of some other element ; (3) when 

 the elements unite chemically, the action takes place between the 

 atoms. If we assume this theory to be correct and argue from it as 

 a basis, w can deduce the laws of definite proportions and multiple 

 proportions. Let us suppose that two certain elements, A and B, 

 unite, and the union is of the simplest kind possible, that is, in each 

 instance an atom of A is united with an atom of B. No matter what 

 the mass of the resulting product may be, whether an ounce, pound, 

 or ton, the whole chemical action is simply a repetition throughout 

 the mass of what might be called the unit action, that is, the union 

 of one atom of A with one atom of B. Hence the ratio between 

 the weights of the elements in the resulting compound, that is, its 

 composition, must be the same as the ratio between the weights of 

 the aton? of A and the atom of B. But the weights of these atoms 

 arc definite and constant, hence the composition of the compound 

 must be constant, or, in other words, the compound is an illustration 

 of the law of definite proportions. By a simple extension of the 

 above argument, the law of multiple proportions may be deduced. 

 The theory also accounts for the fact that if two elements are brought 

 together in other than certain proportions, say 56 parts of iron to 32 

 parts of sulphur, after union has taken place, part of the one or the 

 other element is found uncombined. It is easy to see, too, that, if 

 the theory is correct, the elements ought to combine according to a 

 system of figures such as were discussed above as combining weights, 

 for these weights are bound to be proportional to the weight of atoms, 

 which are definite. The atomic theory has been found in accord with 

 the facts of chemistry for a century or more, and we are justified in 

 accepting it, although we cannot prove absolutely the existence of 

 atoms. 



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