GLOSSARY 295 



by combining with oxygen. (A base is a compound 

 that in aqueous solution gives hydroxyl ions [HO].) 

 Bases combine with acids and form salts. See Acids 

 and Salt. 



Millimicron. One-thousandth of a micron. (A 

 micron is equivalent to one-thousandth of a milli- 

 meter, or one-millionth of a meter.) A unit for 

 measuring light-waves. 



Molecular Weight. The sum of the atomic weights 

 of all the atoms in the molecule of a compound or 

 element. 



Molecule. Chem. Two or more atoms that are 

 bound together chemically constitute a molecule. 

 The power of atoms to unite with other atoms to 

 form molecules is termed their "valency." The 

 atoms of all the elements except the rare gases 

 (helium, argon, neon, krypton, and xenon) enter 

 into combination with other atoms to give mole- 

 cules. When two or more atoms of the same element 

 are united, they form a molecule of an element. 

 When the combining atoms are of different kinds, they 

 form a molecule of a compound. A molecule con- 

 sists of the smallest number of atoms that will 

 form a given chemical compound. Thus it is the 

 smallest particle of a substance, or compound, that 

 can have an independent existence and retain its com- 

 position and properties . The molecule of most inor- 

 ganic substances is light, and consists of only a small 

 number of atoms. The molecule of most organic 

 substances (carbon compounds) is extremely heavy. 

 Thus, according to Julius B. Cohen, probably few 

 proteins have a molecular weight of less than 10,000. 

 The minimum molecular weight of hemoglobin (the 

 solid coloring-matter of red blood-corpuscles) is 

 estimated at about 16,000. A molecule, an octadec- 

 apeptid (18 amino acid molecules combined), hav- 



