620 



NOMENCLATIVE AND NOTATION, CHEMICAL. 



these four bodies are the same throughout, 

 namely the ordinary molecular, or dilitral vol- 

 ume ; that in the first no condensation in volume 

 has occurred; that in the second there has been 

 a disappearance of 1 volume by condensation, 

 ill the third of 2, and in the fourth of 3 vol- 

 umes. This condensation is carried to still 

 higher degree in types above the fourth here 

 given ; and generally, the condensation in the 

 product-volume increases with the number of 

 elements and of atoms of each entering into 

 the constitution of a compound. As a conse- 

 quence, in compounds of a high order, this 

 normal volume becomes packed with scores 

 of atom-volumes, each originally half its own 

 magnitude ; and the density of the compound gas 

 or vapor, if the body have such form, is corre- 

 spondingly augmented. The molecular weights 

 of elementary and compound bodies of the 

 gaseous form, that is, the weights of their dili- 

 tral volumes, directly represent the specific 

 gravities of such bodies, compared with hydro- 

 gen as 2, or halved (monolitral), with hydrogen 

 as 1. 



Atomicity or Quantivalence of Bodies. Chlo- 

 rine, which in the first of the above types has 

 fixed one atom of hydrogen, tends generally to 

 fix one atom of any element with which it com- 

 bines ; so also of Br and I ; while, like O, also 

 S and Se tend each to fix two atoms ; like N, 

 also P and A tend to fix three atoms ; and like 

 C, also Si and Ti tend to fix four atoms. This 

 fact of the degree of atom-fixing or atom-en- 

 gaging power of an element (the number of 

 atoms it chiefly tends to combine with) con- 

 stitutes, and when known determines, its atom- 

 icity ; and according as elements tend to en- 

 gage 1, 2, 3, 4, or 6 atoms of other bodies, they 

 are by most modern chemical writers said to be 

 mono-, di-, tri-, tetr-, or hex-atomic. 



Hofmann questions the propriety of this use 

 of the terms just given ; and he has substituted 

 for "atomicity" the term quantivalence (quan- 

 tum, how much, valens, availing, or capable 

 of); while, to express the several degrees of 

 quantivalence above indicated, he employs the 

 terms uni-, oi-, tri-, and quadri-valentand for 

 the highest, we may suppose, sexi-valent. He 

 then turns the expressions above given to the 

 new use of marking the number of atoms nor- 

 mally entering into the free molecule of an ele- 

 ment ; according to which use, most elementary 

 molecules are diatonic, while Hg is a monatomic, 

 and P a tetratomic element. The distinction 

 between the equivalence (atomic weight, com- 

 bining proportion, or molecule-forming power) 

 of an element or compound, on the one hand, 

 and the quantivalence (atomicity, atom-fixing 

 and atom-replacing power) of the same body, 

 on the other, must, it is believed, now be 

 sufficiently obvious without further expla- 

 nation. 



Kepresentmg the multiples of equivalents by 

 the small figures placed, as in one form usual, 

 at the right of and below the symbols (thus, 3 , 

 3 , etc.), the coefficient, or number expressing 



the degree of quantivalence, is placed also at 

 the right of the symbol, but above the coeffi- 

 cients in common use being as follows: ' " '" 

 ir T Ti , the first three mere traits, but for which 

 Hofmann, for uniformity's sake, substitutes the 

 numerals ' H iu (hence, O", C' T , etc.). Denot- 

 ing at once both the equivalential and quanti- 

 valential coefficients, expressions such as the 

 following are obtained: O s u , 3 iT , H 4 ', S a u , 

 etc. These double expressions must, of course, 

 in no case be mistaken for fractions; as the 

 two orders of coefficients indicate entirely dif- 

 ferent forms of chemical value or power. Mean- 

 time, it must still more distinctly appear how, 

 in quantivalential power, certain elementary 

 atoms and compound radicals agree; so that 

 not only can the two replace each other, but 

 either tends to replace as many atoms of a mon- 

 atomic element or radical as the number of units 

 in its own quantivalential coefficient. Thus, 

 the triatomic radical glyceryle (CaHs)'' 1 , plays 

 in the constitution of glycerine precisely the 

 same part as the triatomic element aluminium 

 in aluminic hydrate, as follows : 



H 3 > H 3 



while a single equivalent of diatomic calcium 

 may replace in 2HC1 the two equivalents of 

 hydrogen, giving Calls'. It may be added, 

 that for elements and compound radicals, ac- 

 cording to their respective degrees of quantiv- 

 alence, Williamson and Odling adopt the terms 

 monad, dyad, triad, tetrad, etc. 



The Type- Theory not Arbitrary. Among 

 objections to the theory of chemical types, in 

 the form generally accepted, Kolbe in particular 

 (Ann. der Ghem. and Pharm., March, 1860) has 

 urged that the types themselves which have 

 been adopted are artificial and arbitrary. He 

 would, however, introduce a new system, in 

 which, starting with the fact of the origin of 

 organic compounds in a concurrence of C0 a 

 with HiO, he regards an oxide of carbon (say, 

 C,O 4 ) as the type from which all compounds of 

 C., H., and O. may be derived, and assigns for 

 the mono-, bi-, and tri-basic organic acids types 

 consisting of this form and the multiples of the 

 equivalents in it by 2 and 3, while he ad- 

 mits other types also, including that of ammo- 

 nia. Wurtz, in reply, presents arguments in 

 favor of the view that the leading types assumed 

 and the distinctions of bodies corresponding to 

 them actually exist in nature. He says, very 

 pertinently, that a water typo exists because 

 there exists a [class of] diatomic elements, and 

 an ammonia type because there is a [class of] 

 triatomic elements, etc. Thus, the types are 

 determined by a fundamental property of the 

 elements themselves, namely, their power of 

 combining and of substitution, in respect to 

 other elements in a word, by their atomicity. 



The following tabular view of the chemical 

 elements, the indications of which are suffi- 

 ciently explained by preceding statements is 

 adopted in somewhat condensed form from 

 Hofmann's Introduction to Modern Chemistry : 



