his speech is one of the best speeches ever .. he had used many rhetorical devices but we discuss two here :
metaphor :generally the metaphors are the comparison of the things but the metaphors used in the speech are called hard-hitting because these are the metaphors to excite the crowd listening ..like : he rung the bell in great joy to convey the message of freedom ..
Allusions : in the speech he used allusions to make crowd understand clearly..it is the reference to any event ,or a person ..like: i guess my mother thinks me superman that is why she asked me to do so much work.