SECT, xrv.] DEFINITE PEOPOETIONS. 121 



substances will unite with one part by weight of the other, 

 or with two parts, or three, or four, &c., so as to form a new 

 substance ; but in any other proportions they will only be 

 mechanically mixed. For example, one part by weight of 

 hydrogen gas will combine with eight parts by weight of 

 oxygen gas, and form water ; or it will unite with sixteen 

 parts by weight of oxygen, and form a substance called 

 deutoxide of hydrogen ; but, added to any other weight of 

 oxygen, it will produce one or both of these compounds 

 mingled with the portion of oxygen or hydrogen in excess. 

 The law of definite proportion established by Dr. Dalton, 

 on the principle that every compound body consists of a 

 combination of the atoms of its constituent parts, is of uni- 

 versal application, and is in fact one of the most important 

 discoveries in physical science, furnishing information pre- 

 viously unhoped for with regard to the most secret and 

 minute operations of nature, in disclosing the relative weights 

 of the ultimate atoms of matter. Thus an atom of oxygen 

 uniting with an atom of hydrogen forms the compound water ; 

 but, as every drop of water however small consists of eight 

 parts by weight of oxygen and one part by weight of hydro- 

 gen, it follows that an atom of oxygen is eight times heavier 

 than an atom of hydrogen. In the same manner sulphuretted 

 hydrogen gas consists of sixteen parts by weight of sulphur 

 and one of hydrogen ; therefore an atom of sulphur is sixteen 

 times heavier than an atom of hydrogen. Also carbonic 

 oxide is constituted of six parts by weight of carbon, and 

 eight of oxygen ; and, as an atom of oxygen has eight times 

 the weight of an atom of hydrogen, it follows that an atom 

 of carbon is six times heavier than one of hydrogen. Since 

 the same definite proportion holds in the composition of all 

 substances that have been examined, it may be concluded 

 that there are great differences in the weights of the ulti- 

 mate particles of matter. M. Gay Lussac discovered that 

 gases unite together by their bulk or volumes, in such simple 

 and definite proportions as one to one, one to two, one to 



