26 PRINCIPLES OF CHEMISTRY 



Scandium, Sc =44. Indium, In =11 3, 



Gallium, Ga=68. Tellurium, Te = 12. r >. 



Germanium, Ge= 72. Caesium, Cs=132. 



Rubidium, Rb=S5. Lanthanum, La]=138. 



Yttrium, Y =89. Didymium, Di =143. 



Niobium, Nb=94. Ytterbium, Yb=173. 



Ruthenium, Ru=104. Tantalum, Ta =182. 



Rhodium, Rh= 1 04. Thorium, Th = 234. 



Besides these 66 elements there have been discovered : Erbium, 

 Terbium, Samarium, Thallium, Holmium, Mosandrium, Phillipium, 

 Vesbium, Actinium, and several others. But their properties and com- 

 binations, owing to their extreme rarity, are very little known, and even 

 their existence as independent substances 28 is doubtful. 



It has been incontestably proved from observations on the spectra 

 of the heavenly bodies that many of the most common elements (such 

 as H, Na, Mg, Fe) occur on the far distant stars. This fact confirms 

 the belief that those forms of matter which appear on the earth as 

 elements are widely distributed over the entire universe. But why, 

 in nature, the mass of some elements should be greater than that of 

 others we do not yet know. 



The capacity of each element to combine with one or another 

 element, and to form compounds with them which are in a greater or 

 less degree prone to give new and yet more complex substances, forms 

 the fundamental character of each element. Thus sulphur easily com- 

 bines with the metals, oxygen, chlorine, or carbon, forming stable sub- 

 stances, whilst gold and silver enter into combinations with difficulty, 

 and form unstable compounds, which are easily decomposed by heat. 

 Compounds, and also elements, may be divided into two classes those 

 which easily enter into many different chemical changes, and those which 

 enter into but few combinations, which are characterised by their small 

 capacity for the direct formation of new, more complex substances. 

 The cause or force which induces substances to enter into chemical 

 change must be considered, as also the cause which holds different 

 substances in combination that is, which endues the substances 

 formed with their particular degree of stability. This cause or force 

 is called affinity (affinitns, affinite, verwandtsckaft), or chemical affinity. 29 



28 It may be that some of them are compounds of other already-known elements. 

 Pure and incontestably independent compounds of these substances are unknown, and 

 some of them have not even been separated but are only supposed to exist from the 

 results of spectroscopic researches. There can be no mention of such contestalilc and 

 doubtful elements in a short general handbook of chemistry. 



29 This word, first introduced, if I mistake not, into chemistry by Glauber, is based on 

 the idea of the ancient philosophers that combination can only take place when the sub- 



