992 TjiAXSACTIOiXS OF THE AMERICAN INSTITUTE. 



bodies containing only two elements when the atoms of both elements 

 arc duplicated, because such duplication involves an unequal decrease 

 in their normal atomicity. However, in a homologous hydrocarbon 

 series, in which tlie number of atoms of each element forming a 

 molecule increase by arithmetical progression, the lowest supposable 

 combination will be the measure of the atomicity of the sum of the 

 carbon atoms in every member of the series ; for example, the body 

 not yet isolated, consisting of one atom of carbon and tM'^tatoms of 

 hydrogen, would have a combining power expressed by 4 — 2; 

 accordingly we find that ethylene, and every other homologue has 

 the value of a dyad, and may be united with two atoms more of 

 hydrogen. Thus in the hydride of methyl series, the saturating 

 power of a given number of condensed carbon atoms is expressed by 

 the number of hydrogen atoms in the combination, wiiich is the 

 measure of the power of the same number of carbon atoms in other 

 bodies ; for example, the composition of hydride of ethyl proves that 

 two atoms of carbon play the part of a hexad, therefore the satura- 

 ting power of acetylene, composed of two atoms of carbon and two 

 of hydrogen is expressed by 6 — 2. This branch of the subject can- 

 not be presented even in outline without the use of symbols ; and as 

 the symbols I use are not yet generally adopted, and might divert 

 attention from the principal points to be elucidated, I do not propose 

 to introduce them in the present paper. 



Our subject in its broadest meaning includes mvestigations relating 

 to the diversity of composition in chemical bodies. The cause of 

 this diversity may be assigned in a general way to affinity, by affirm- 

 ing that a powerful electro-positive element combines most directly 

 and intimately with a powerful electro-negative, producing at once a 

 compound in the most condensed state ; as for example, sodium and 

 chlorine in forming common salt, while elements having less affinity 

 may unite by degrees in a variety of Ibrms, as seen in the combina- 

 tions of oxygen with nitrogen, sulphur and the halogens. This 

 tendency to diversity is more remarkable among metalloids than 

 among metals, for the latter, with one exception, are solids, and in 

 general, are not readily brought into the liquid and gaseous states. 



Kothing in the whole range of nature's operations excites greater 

 ^vonder than* the fact that a large majority of the chemical bodies 

 derived fi-om the organic kingdom are composed of the same three or 

 four elements, which by diversity of combination give as great a 

 varietv of characteristics. In anmionia, nitric acid, laughing gas, 



