SECT. XIV. DEFINITE PROPORTIONS. Ill 



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 universal application, and is in fact one of the most 

 important discoveries in physical science, furnishing information 

 previously 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 hydrogen, 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 hydro- 

 gen ; 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 a vast number of substances that have been 

 examined, it has been concluded that there are great diiferences 

 in the weights of the ultimate particles of matter. Although 

 Dalton's law is fully established, yet instances have occurred 

 from which it appears that the atomic theory deduced from it is 

 not always maintained. 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 three, &c. 

 For example, one volume or measure of oxygen unites with two 

 volumes or measures of hydrogen in the formation of water. 



Dr. Faraday has proved, by experiments on bodies both in 

 solution and fusion, that chemical affinity is merely a result of 



