Proceedings of the Polytechnic Association. 989 



is more complex ; but nitrogen is the most complex of all, in which 

 Bome fourteen lines are seen. 



Common air shows a mixed composition. The weakest of liquid 

 homoeopathic medicines, the components of which could not be 

 detected by chemical analysis, are visible under the spectroscope. On 

 burning a few grains of gunpowder, by the aid of this important 

 instrument, its composition can be determined. 



The following is one of the papers read at Chicago, which were 

 alluded to at the first September meeting of this association. 



Ok the Combining Power of Chemical Elements. 



Read before the Americau Aesociation for the advancement of science, by Professor S, D, Tillman, 

 of the American Institute, New Yofk. 



Since the promulgation of the doctrine of types and substitutions, 

 the saturating powers of chemical bodies have been quite satisfac- 

 torily represented by symbols. The prominence which the subject 

 of atomicity has recently assumed is partly the result of the plain and 

 simple manner of illustrating it. By means of the new notation, and 

 several additional characters or signs, an ideal structure of a chemical 

 body is represented ; for of the real structure nothing is known. In 

 it the saturating power of an atom, or a combination of atoms, is 

 measured by degrees, the lowest power being taken as the unit of 

 measurement. A given numl)er of combining units require a like 

 number of other combining units to complete the structure. The new 

 body is always the result of duality, and its fonn or type will be 

 retained while its chemical functions may be entirely changed by 

 displacement ; for certain parts of the structure may be removed 

 provided a substitution of the same equivalence is made to preserve 

 the molecular equilibrium. Thus the chemist assigns substitution 

 values to every simple and complex radical, and designating them 

 by numbers, from one up to six, is prepared to combine his symbols 

 in a process of matching, which, although quite as simple as 

 that with dominoes, affords the highest satisfaction, because it is 

 always associated with the order, rapidity and precision of mole- 

 cular changes. Yet this kind of chemical reckoning has one 

 •serious drawback, namely, the atomicity of the same element is not 

 an invariable value. It is often decreased l)y a duplication of similar 

 atoms, and, in some remarkable instances among monads, it seems to 

 be increased beyond its normal energy by a kind of induction which 

 has not yet been accounted for. Saturating power depends on causes 



