528 THE PRINCIPLES OF SCIENCE. [CHAP. 



to account for the particular group of qualities belonging to 

 each element, but there are multitudes of particular facts 

 of which no further account can be given. Why should 

 the sulphides of many metals be intensely black ? Why 

 should a slight amount of phosphoric acid have so great 

 a power of interference with the crystallisation of vanadic 

 acid ? l Why should the compound silicates of alkalies and 

 alkaline metals be transparent ? Why should gold be so 

 highly ductile, and gold and silver the only two sensibly 

 translucent metals ? Why should sulphur be capable of 

 so many peculiar changes into allotropic modifications ? 



There are whole branches of chemical knowledge which 

 are mere collections of disconnected facts. The properties 

 of alloys are often remarkable ; but no laws have yet been 

 detected, and the laws of combining proportions seem to have 

 no clear application. 2 Not the slightest explanation can 

 be given of the wonderful variations of the qualities of iron, 

 according as it contains more or less carbon and silicon, nay, 

 even the facts of the case -are often involved in uncertainty. 

 Why, again, should the properties of steel be remarkably 

 affected by the presence of a little tungsten or manganese ? 

 All that was determined by Matthiessen concerning the 

 conducting powers of copper, was of a purely empirical 

 character. 3 Many animal substances cannot be shown to 

 obey the laws of combining proportions. Thus for the most 

 part chemistry is yet an empirical science occupied with 

 the registration of immense numbers of disconnected facts, 

 which may at some future time become the basis of a 

 greatly extended theory. 



We must not indeed suppose that any science will ever 

 entirely cease to be empirical. Multitudes of phenomena 

 have been explained by the undulatory theory of light ; 

 but there yet remain many facts to be treated. The 

 natural colours of bodies and the rays given off by them 

 when heated, are unexplained, and yield few empirical 

 coincidences. The theory of electricity is partially under- 

 stood, but the conditions of the production of frictional 

 electricity defy explanation, although they have been 



1 Roscoe, Bakerian Lecture, Philosophical Transactions (1868), 

 vol. clviii. p. 6. 



2 Life of Faraday, vol. ii. p. 104. 



3 Wat 



fatts, Dictionary of Ck&mistry, voL ii. p. 39, &c. 



