412 
THE CONSTITUTION OF MATTEU. 
ments, that, in nearly all cases of chemical combination, the compounds formed 
consist of definite and invariable proportions by weight of the constituents em¬ 
ployed. This is the leading fact which cannot be disputed. A study of its 
different features has led to three great general statements, known as the law 
of definite proportions; the law of reciprocal proportions; and the law of multiple 
proportions. 
The first of these is simply an enunciation of the rule just stated: “Thus, 
water, which consists of one part by weight of hydrogen united to eight parts 
of oxygen, cannot be formed by the same elements in any other than these pro¬ 
portions. You can neither add to nor subtract from the normal ratio of the 
elements without entirely altering the nature of the compound. 7 ’ 
It must be stated, however, that all the best and most careful experiments 
have been made only upon the simplest compounds, such as metallic salts. It 
yet remains to be proved whether there are not numerous instances of combina¬ 
tion occurring in indefinite proportions. There seem to be instances of such 
combination when the attraction between the uniting elements is of a feeble 
character. 
The second law quoted asserts that when chlorine, for example, unites with 
oxygen and with carbon, the proportions of oxygen and carbon in the compounds 
so formed are those in which they will themselves unite together, or, as the law 
of multiple proportions telle us, are simple multiples or fractions of those pro¬ 
portions. Upon these three “laws,” which, be it observed, are merely general 
formulae expressing what had been observed in a number of individual instances, 
Dalton based his atomic theory, explaining the combination of masses of matter 
in invariable proportions by the hypothesis of their being constructed of par¬ 
ticles of definite size and weight and indivisible. As before observed, this can¬ 
not be directly inferred. “ All which observation teaches us is, that if there be 
such particles they are smaller than the smallest observable quantities.” At 
the present day, however, we may safely say that there are few, if any, chemists 
who believe as implicitly in the atoms of Dalton as he did himself. Dalton 
seems to have been utterly uncompromising in his notions on this matter. 
lie even explains such phenomena as “ the opacity of metals and their lustre ” 
by the hypothesis that “ a great quantity of solid matter and a high condensa¬ 
tion of heat are likely to obstruct the passage of light, and to reflect it.” The 
really valuable portion of Dalton’s work was the discovery of the laws of mul¬ 
tiple and reciprocal proportion. 
The atomic theory is now received as the basis of a most valuable method of 
expressing, in a manner intelligible to the mind, a vast body of facts, and giv¬ 
ing the whole a systematic form. “ The real experimental import of the equi¬ 
valent numbers is the expression of the proportional and relative weights of 
bodies in which they produce equivalent effects in chemical combinations, and 
these effects we represent to our minds and render intelligible by ascribing 
them to indivisible particles or ‘ atoms ’ which occupy a certain space, and 
possess a certain form or shape.”* So that the idea is employed simply as a 
metaphor. When we begin to inquire what these atoms are which are so 
freely handled and discussed, what is their nature, are they really indivisible 
ultimate particles? we are led away into another region into which chemistry 
can follow with but halting steps, if at all. 
The President of the Chemical Society has recently been giving an elaborate 
defence of the atomic theory ; it cannot but be surmised that there exists at the 
preseut time more than a small amount of disaffection from the theory, or such 
a defence could not have been called for. 
It will be useful to recall the principal properties of matter, by the study of 
* Liebig’s Letters, p. 103. 
