Size-reduction of materials is an important operation in many chemical industries. The purpose of size-reduction are: (a) for specific mesh size product; (b) grinding for release, or unlocking grinding for purposes of surface exposure or locked-in products for chemical or physical attack; (c) specific surface grinding for product; and (d) size modulus, where limited mesh size is needed for specific processing operation. Size-reduction is accomplished by (a) impact, (b) differential movement of adjacent surfaces and (c) by the combination of both. Most size-reduction of a combination of both, whereas swing hammermill grinding is due mainly to impact. Rittingers’ and Kicks’ laws are empirical formulas which do not make an attempt to resolve the forces as applied to grinding into their component parts. Possibly the application of the component forces as applied to impact grinding would give a key to the multiple factors controlling size-reduction. If this can be worked out, the general formula might be obtained that would apply to all phases of size-reduction. The purpose of this investigation is to study the factors as applied to swing hammermill grinding; also, to determine if it is possible to formulate an equation which will hold for the size reduction of various materials. / Master of Science