300 W H AT IS LIFE 



proof. A wealth of experimental work thus has 

 proved Planck's element of action to be indeed a 

 universal constant. However, though the quantum 

 theory so far as h is concerned has been generally 

 accepted as fully established, not many have been 

 ready to accept Einstein's "extreme quantum theory" 

 of discrete, or corpuscular, "light-quanta." Recently 

 (1923), direct and, it would seem, convincing proof 

 of Einstein's theory of light-quanta has been fur- 

 nished by the Compton effect. But serious difficul- 

 ties remain, and must be cleared up before various 

 phenomena that have been accounted for on the 

 wave-theory can be harmonized with the quantum 

 theory. See Energy, Photoelectric Effect, and Comp- 

 ton Effect. 



Radical. Chem. A group of atoms which enters 

 into chemical combinations, acting as a single ele- 

 ment, and that can pass unchanged through many 

 chemical transformations. 



Salt. Chem. A compound that is produced when 

 the hydrogen of an acid is replaced by an electro- 

 positive element or radical. See Acid, Electrolyte, 

 and Electrolytic Dissociation. 



Simiidae. An African and Asiatic family of apes. 



Sols. Colloidal solutions. 



Solution. 1. The term is generally understood 

 to refer to the liquid phase, but solutions may also 

 exist in the solid, and gaseous phases. A solution 

 is "a single homogeneous phase made up of two or 

 more components and whose compositions may vary 

 within certain limits." In the liquid phase the liquid 

 is known as the solvent^ and the substance dissolved 

 in it, as the solute. 2. The process of dissolving a 

 substance in a solvent. 



Sorption. A general term denoting all cases in- 

 volving more than one of the factors, adsorption, 



