The Butler Libraries us the Library of Congress (LC) classification scheme for its materials. This is an alpha-numeric system. Each call number begins with a letter or letters followed by a number designating a particular topic. In music, all books and scores are classed wtih the letters "M," "ML," or "MT."
M = Scores
ML = Books about music (i.e., music literature or history)
MT= Materials about music theory or pedagogy (i.e., teaching materials)
Simplified overview of the LC classes relevant to the study of the piano:
Analytical guides: MT140+
Bibliography: ML128.P3
Discography: ML 156.4 P5
Graded lists: ML132.P3
Dictionaries: ML102.P5
Pianists: ML397 (Collected biography), ML417 (Biographies of individual performers)
Biographies of individual composers (cuttered by last name of composer): ML410
History and criticism: ML650+
Construction: ML652+
Instruction and study (studies, methods, etc.): MT220+(MT252)
Accompaniment: MT239
For children: MT745+
Four hand-Two pianos: MT242
Instrumental music: M20+
Duets: M200+
Detailed breadkown of score designations:
M20 - M39 Piano music (Solo)
M20 - M22 Collections
M23 Sonatas
M24 Suites
M25 Other separate works
M26 Piano, 1 hand
M27 Variations
M28 Marches
M30 - M32 Dances (polkas, polonaises, waltzes, etc.)
M32.8 - M39 Arrangements for piano
M198 - M216 Piano (4 hands, 2 pianos, etc.)
M310 - M344 Trios with piano
M410 - M444 Quartets with piano
M510 - M549 Quintets with piano (there are also separate numbers for sextets, septets, octets, and nine or more instruments under add'l. nos.)
M1010 - M1011 Piano with orchestra
M1110 - M1111 Piano with string orchestra