338 ORGANIC CHEMISTRY. 



856. ARRANGEMENT OF ATOMS. At a loss 



How are the 



above facts ac- for any other way of accounting for such 

 counted for? difference o f properties, we are compelled 

 to believe that it is because of difference of atomic 

 arrangement. We have seen, in the case of iodide 

 of mercury, mentioned in a former chapter, that a 

 mere touch, which produces motion and re-arrange- 

 ment of its atoms in smaller groups, at the same time 

 changes the color of the compound from yellow to red. 

 Now the molecule of lactic acid, although containing 

 the same relative proportion of all of its constituents, 

 is smaller than the molecule of sugar of milk. It con- 

 tains six atoms of carbon, six of hydrogen, and six of 

 oxygen. The molecule of sugar of milk contains 

 twelve of each, and can therefore furnish material to 

 make two of acid, as it does in the souring of milk. 

 And we may suppose that the change from sweet to 

 sour is owing to this subdivision of the molecules. 



857. There are other cases of identical 



How is diver- . , . -, -, T rr 



sity of prop- composition, in which there is no difference 

 countedfor whatever in the size of the molecule, or the 



when there is number of atoms which enter into its corn- 

 no difference . . . ., ., 



of compost- position. This is the case with the oils of 

 tionor size? turpentine, lemon, and pepper, and perhaps 

 with wood, starch, and sugar. The molecules of each 

 are composed, not alone of the same proportion of the 

 elements which enter into its composition, but, as there 

 is reason to believe, of the same number of atoms of 

 each. We are therefore compelled to look for the differ- 

 ence which shall account for their peculiar property, in 

 a different arrangement of atoms, inside of the mole- 



