48 HOW CROPS GKOW. 



Element. At. wt. Symbol. 



Hydrogen 1 H 



Carbon 12 C 



Oxygen 16 O 



Nitrogen 14 N 



Sulphur 32 S 



Phosphorus 31 P 



Chlorine 35.5 Cl 



Mercury 200 Hg (Hydrargyrum) 



Potassium 39 K (Kalium) 



Sodium 23 Na (Natrium) 



Calcium 40 Ca 



Iron 56 Fe (Ferrum) 



Multiple Proportions, When two or more bodies unite 

 in several proportions, their quantities, when not expressed 

 by the atomic weights, are twice, thrice, four, or more times, 

 these weights ; they are multiples of the atomic weights by 

 some simple number. Thus, carbon and oxygen form two 

 commonly occurring compounds, viz., carbonic oxide, con- 

 sisting of one atom of each ingredient, and carbonic acid, 

 which contains to one atom, or 12 parts by weight, of car- 

 bon, two atoms, or 32 parts by weight, of oxygen. 



Molecular Weights of Compounds, While elements 

 unite by indivisible atoms, to form compounds, the 

 compounds themselves combine with each other, or 

 exist as molecules^ or aggregations of atoms. It has 

 indeed been customary to speak of atoms of a com- 

 pound body, but this is an absurdity, for the smallest par- 

 ticles of compounds admit of separation into their elements. 

 The term molecule implies capacity for division just as 

 atom excludes that idea. 



* Latterly, chemists are mostly inclined to receive as the true atomic weights 

 double the numbers that have been commonly employed, hydrogen, chlorine, 

 and a few others excepted. 



t Latin diminutive, signifying a little mass. 



