IT)!^ THE MODERN THEORY OF CHEMICAL TYPES. 



which corrcppoiulod to the "order;" a "chemical" type to the "genus;" aud 

 the various meniberd under the same chemical type corresponded to the 

 " species." 



Compounds of the same molecular type consisted of the same number of 

 atoms; hut not in binary groups, as the electro-chemical theory required. 



Under each molecular type were the chemical types, consisting of tin; same 

 number of atoms (as before) but similarly arranged. The individuals of the 

 Bamc chemical type consisted of the same number of atoms, similarly arranged, 

 but dirtering iu the kind of atoms. The following example will illustrate the 

 theory : 



MOLECULAU TYPE OF TWELVE ATOMS. 



, , 1 . 1 X f Acetic acid 04114^)1 > Individuals of 1st chemical 



1st chemical type J (ji,io,aeeticacid. 04 01,1104 ] type. . 



-, 1 , . 1 ^ i Alcohol C4 He O2 ) Individuals of 2d chemical 



2d chemical type <,r . r^ n i^ } + 



•^ ^ ( iUercaptan O4 tie b-z } type. 



These all bi-loug to the same molecular type of twelve atoms. The iirst 

 two and the last two belong, respectively, to the same rliemlcul type; the atoms 

 are regarded as being similarly arranged, because acetic and chloracetic acids, 

 on the one side, and alcohol and mercaptan on the other, bear a great analogy 

 to each other in their compounds and in the proilucts of their decomposition by 

 the same reagents. The following method was adopted for writing the for- 

 mulfe according to this theory : 



Acetic acid O4 ^^ [ O4 



Chloracetic acid C4 yy^ > O4 



Acetate of potassa C4 ,.^ > O4 



Acetic ether C4 ,.-, v'r \ ^ O4 



(U4il5J ) 



Chloracetic ether C4 ,^\i . \ O4 



V^4-t-t5J ) 



The following contain Cg Ilg O4, but the atoms are arranged differently 



Butyric acid Cg ^' I O4 



Acetic ether ^•^ fO H) 1 ^-^ 



Propionate of methyle Cg /^ il \ ? O4 



It will be observed that chlorine, in the type, takes the place of the upper 

 hydrogen atoms and potassium, and the radicals the place of the lower ones, 

 thus indicating the diiTerent nature of the several hydrogen atoms iu the type ; 

 and, furUier, that this theory was obliged to assent to the idea of " radicals," 

 namely, groups of atoms playing the part of single atoms. 



The type theory met with many supporters, some of them the best thinkers 

 which have enriched modern chemistry ; it met with many variations, some 

 of which penetrated far into the realms of fancy; but it would probably have 

 fallen into disuse had not the discovery of the compound ammonias directed 

 the att(!Utioa of the chemical world to this method of imagining the constitution 

 of chemical compounds. 



At the same time that attention to this subject was arrested, homologous 

 scries were discovered, (by a type theorist,) and important laws with respect, 

 to them, such as the relative boiling points of their members, their vapor den-> 



