CIIEMISTEY. 



the vegetable tissue will be attacked, and the cloth will 

 become more or less rotten from the destruction of some 

 of its molecules. 



414. Difference in Properties with Similarity of Composi- 

 tion. There is often found in organic chemistry great sim- 

 ilarity of composition with wide difference in properties. 

 We will give a few examples. Alcohol, cotton, sugar, and 

 acetic acid are four substances certainly not much alike in 

 their properties, and yet these widely dissimilar bodies are 

 made of the same elements carbon, hydrogen, and oxygen. 

 By examining the formulae of these bodies, here given, 



Alcohol C 2 H 6 O I Grape sugar .C 6 H 12 O 6 



Cotton C 6 H 10 O 5 Acetic acid C 2 H 4 O 2 



you will see that these three elements are combined in very 

 different proportions ; and this illustrates as well the com- 

 plexity of the molecules referred to in 412, for each of the 

 formulae above represents one molecule. We have select- 

 ed only four bodies made of these three elements, but act- 

 ually there are many thousands of bodies composed of 

 these three elements only. 



415. Isomerism. Strange and mysterious as these facts 

 appear, a much more apparently inexplicable feature re- 

 mains to be shown. Examine closely the formulae of the 

 last two bodies named, grape sugar and acetic acid ; you 

 see that if we should multiply by three the little figures, 

 or co-efficients, of the atoms of C, H, and O in acetic acid, 

 we will get the formula of grape sugar ; thus : 



Acetic acid = C 2 H 4 O 3 

 . 3 



Grape sugar = C 6 H 12 O 6 



Here, then, we have two bodies made up of the same 

 elements in the same proportion, and differing only in their 

 molecular weights, and yet how different in their proper- 



