chlorine. The equation forms a short and con- 

 venient plan of recording the facts of experiment. 



Nature does not always permit man to mix things 

 in any proportion he pleases. She does sometimes, 

 if he only uses the attractions of adhesion or cohe- 

 sion in binding the material together; but if he 

 employs chemical attraction, she restricts him to 

 special proportions. That is to say, if the things 

 mixed do not attack one another or intimately com- 

 bine then admixture may be effected in any propor- 

 tion; and the mixture is a mere mixture having the 

 mean properties of its components. 



When compounds unite to form definite chemical sub- 

 stances, they always combine in the same proportions. 



A definite compound always contains the same elements 

 in the same proportions. 



While many substances only unite chemically in 

 one proportion, others combine in two or even more. 



When two elements unite in more than one proportio?i, 

 the resulting compounds cojitain, to a constant proportion 

 of one element, simple multiple proportions of the other 

 or the weights of the constituent elements bear some similar 

 simple relations to each other. 



ATOMIC WEIGHTS. It is a fact, that, when ele- 

 ments unite with one another in the peculiar and 

 intimate manner termed chemical, they do not com- 

 bine in the haphazard proportions of a mere mix- 

 ture, but in one fixed and constant proportion. Such 

 proportions or weights represent the weights of their 

 atoms. Oxygen unites with other elements in pro- 

 portions of 16, therefore 16 is the weight of the atom 

 of oxygen. Chlorine unites with other elements in 

 proportions of 35^, therefore 35^ is the atomic 

 weight of chlorine. And for a similar reason the 

 atomic weights of hydrogen will be I, carbon 12, and 

 iodine 127. It will be understood that these are the 



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