4 PLAN OF THE WORK. 



still, because it possesses affinities, and produces in combination, re- 

 sults entirely similar to those of the combustibles, is thrown into the 

 same class, for the purpose of bringing forward the important acids 

 and oxides of which it is the basis. 



Two of the least important of the simple combustibles, boron and 

 selenium, are reserved until this period : their history bears no very 

 important relation to that of most of the other bodies, but, as they too 

 form acids, they are disposed of in the train of the other combustibles, 

 and of the great agents that sustain combustion. 



Fluoric acid, which although undecomposed, has without doubt, a 

 combustible base, is naturally assigned to the same place, in the class- 

 ification, and from its combining, in an interesting manner, with boron, 

 it comes immediately after that body, and before selenium, whose 

 character is rather anomalous, but more allied perhaps to the combus- 

 tibles than to the metals, where many have placed it. 



6. Chlorine and Iodine and Bromine are introduced after the ele- 

 mentary non-metallic combustibles have been described, and at a pe- 

 riod when, as already intimated, their history becomes intelligible. 



The history of bodies, thus far described, embraces a great part 

 of the philosophy of chemistry, and no small part of the most im- 

 portant facts of the science. If we were to name any portion of 

 chemistry, that is more splendid in its experiments, and more afflu- 

 ent in important results, than another, it would be that which is in- 

 cluded in the history of the elementary combustible bodies, especial- 

 ly when we add their relation to chlorine and iodine, which follow im- 

 mediately after the simple inflammables. 



7. The metals come next, and their history includes all the re- 

 maining elementary bodies. There is a general agreement among 

 authors, as to the place which most of the metals are to occupy in a 

 systematic arrangement, and no one at present thinks of presenting 

 them, as some formerly did, in the beginning, along with other ele- 

 mentary bodies. It is true that some of them are used in the de- 

 monstrations that precede, but as most of the facts are familiar, and 

 the phenomena intelligible, this creates no difficulty ; every one can 

 understand, for instance, how iron decomposes water, and he will 

 comprehend how sulphuric acid aids in that process, just as well be- 

 fore as after he has studied the properties of iron and of the other 

 metals. 



II. ORGANIC BODIES. 



They owe their particular modes of existence, to the joint action 

 of the laws of life and of matter. 



There is, of course, nothing elementary in this part of the subject. 

 Both animals and plants must derive their elements from the unor- 



