CHEMICAL AFFINITY. 149 



of iron will combine with twelve parts by weight of oxygen, 

 and twenty-seven parts of iron will also combine with ten and 

 two-third parts of oxygen. Thus, if we retain the unit of iron 

 we must subdivide the unit of oxygen, or if we retain the unit 

 of oxygen we must subdivide the unit of iron, or we must 

 subdivide both by a different divisor. What then becomes of 

 the notion of an atom or molecule physically indivisible ? 



If iron were the only substance to which this difficulty 

 applied, it might be viewed as an unexplained exception, or 

 as a mixture of two oxides ; or recourse might be had to a 

 more minute subdivision to form the units or equivalents of 

 other substances ; but numerous other substances fall under a 

 similar category ; and in organic combinations, to preserve the 

 atomic nomenclature, we must apply a separate multiplier 

 or divisor to far the greater number of the elementary consti- 

 tuents, i.e. we must divide that which is, exhypothesi, indivisible, 



Thus, to take a more complex substance than any formed 

 by the combination of iron and oxygen, let us select the sub- 

 stance albumen, composed of carbon, hydrogen, nitrogen, 

 oxygen, phosphorus, and sulphur. In this case we must either 

 divide the atoms of phosphorus and sulphur so as to reduce 

 them to small fractions, or multiply the atoms of the other 

 substances by extravagant numbers ; thus, to preserve the 

 unit of one of the constituents of this substance, chemists say 

 it is composed of 400 atoms of carbon, 310 of hydrogen, 120 

 of oxygen, 50 of nitrogen, 2 of sulphur, and I of phosphorus. 

 This is a somewhat extreme case, but similar difficulties will 

 be found in different degrees to prevail among organic com- 

 pounds ; in very many no constituent can be taken as a unit 

 to which simple multiples of any of the others will give their 

 relative proportions. By the mode of notation adopted, if any 

 conceivable substance be selected, it could, whatever be the 

 proportions of its constituents, be formulated as atomic. A 

 solution of an ounce of sugar in a pound of water, in a pound 

 and a half, in a pound and a quarter, in a pound and a tenth, 

 might be expressed in an atomic form, if we select arbitrarily 

 a multiplier or divisor. 



In the case of solution, different proportions can be 

 united up to the point of saturation without any difference 



