430 Notes on Organic Chemistry. 



factured atmospheric air. In this compound the two con- 

 stituents will behave just as might be expected from mere 

 dilution. The oxygen does not, in anyway, alter its properties, 

 but they are reduced in euergy by the admixture of nitrogen. 

 No microscope can exhibit the molecules of either gas, so that 

 we cannot tell, by that mode of examination, that a molecule of 

 oxygen and another of nitrogen lie in juxtaposition, as we 

 found the particles of charcoal and of chalk. We can, however, 

 devise experiments which lead to the conclusion that atmo- 

 spheric air is only such a mixture ; and as oxygen is heavier 

 than nitrogen, it would separate and fall to the bottom if gases 

 did not possess a property of inter diffusion ; so that, if we have 

 two bottles, one above the other, connected with a long narrow 

 tube, and fill the lower bottle with oxygen, and the higher one 

 with nitrogen, they will, in opposition to gravity, mix very 

 thoroughly together. In a chemical combination, the elements 

 are so combined as to form a new substance, which usually 

 differs from both constituents. Thus two dry gases, oxygen 

 and hydrogen, form water, which bears no resemblance to one 

 or the other. Chemical compounds differ from mechanical 

 mixtures in being of a definite character — exactly eight parts 

 by weight of oxygen and one of hydrogen form water, and it 

 cannot be made with either more or less. If the hydrogen be 

 taken from the water, and carbon substituted, we may obtain 

 an oxide of carbon, instead of an oxide of hydrogen ; but in the 

 new compound, six parts by weight of carbon will exactly replace 

 the one part by weight of hydrogen, and neither more nor less 

 will do, though two parts of the oxygen will combine with one 

 part of the carbon, and form a more highly oxygenated compound. 

 The general law is that bodies combine in definite proportions, 

 which bear to each other a certain relation of weight ; and if 

 they combine in more than one proportion, the higher com- 

 pounds will contain some simple multiple of the weight found 

 in the lowest compound. Thus, if oxygen and hydrogen are 

 found in a thousand compounds, they will stand related to 

 each other in such compounds by weight, either as 8 is to 1 , 

 or any simple number of times 8 is to any simple number of 

 times 1. 



The simplest sort of chemical compound is when a single 

 atom or equivalent of one substance is combined with a single 

 atom of another substance. A more complicated compound 

 may consist of single equivalents of two bodies, each composed 

 of two separate substances ; and we may ascend in the scale 

 of complexity until we reach substances containing a great 

 many atoms of several elementary bodies, all united to form a 

 chemical whole. In the mineral world we find a comparative 

 simplicity of composition, often accompanied by great stability ; 



