Are there any literary devices used in Act III of "Romeo and Juliet"?
Early in act 3, Benvolio encourages his friends to find a cool place to go and rest; he wants to avoid a fight with the Capulets. He says, "For now, these hot days, is the mad blood stirring" (3.1.4). He means that when it's this hot outside, people get angry and are more prone to fighting. Therefore, it isn't really their blood that gets "mad"; rather, the idea of mad blood refers to angry people. This is called synecdoche, when a part of something is substituted for the whole.
Mercutio argues with Benvolio, however, claiming, "Thou—why, thou wilt quarrel with a man that hath a hair more or less in his beard than thou hast. Thou wilt quarrel with a man for cracking nuts, having no other reason but because thou hast hazel eyes" (3.1.18-22). These are two examples of hyperbole, or overstatement, when someone exaggerates the truth in order to emphasize that truth. Mercutio insists that Benvolio is as apt to fight as he, as Benvolio will fight someone because of the number of hairs in his beard or because he is cracking nuts. These are overstatements because we don't really believe that Benvolio is so combative, especially having witnessed him trying to break up a fight earlier in the play.
Mercutio then employs understatement when asked if he's hurt (after he fights Tybalt). He says, "Ay, ay, a scratch, a scratch. Marry, 'tis enough" (3.1.97). His injury is actually much more than a scratch; it is a fatal wound. It is more than "enough" to kill him. He then employs a pun when he tells Romeo, "Ask for me tomorrow, and you shall find me a grave man" (3.1.101-102). The word grave means serious but it is also a hole in which you bury someone. Mercutio knows that he will be dead by tomorrow, a serious condition indeed.
Juliet employs an allusion at the beginning of scene 2, as she waits for Romeo to come to her bedroom. She says, "Gallop apace, you fiery-footed steeds, / Towards Phoebus' lodging. Such a wagoner / As Phaeton would whip you to the west / And bring in cloudy night immediately" (3.2.1-4). She refers to figures in Greek mythology, Apollo, a god associated with the sun, and to the sun-god's son, a boy named Phaeton, who drove the sun god's chariot and lost control of it when the horses ran too fast and set the world afire, plummeting into the sea. Juliet is anxious for night to come, and she wants the sun to set now.
She also uses a simile to compare her excitement to that of a child's before a feast day. She says, "So tedious is this day / As is the night before some festival / To an impatient child that hath new robes / And may not wear them" (3.2.30-33). A simile is a comparison of two unalike things using the word like or as.
Yes, there are a few examples of literary devices used in Act III, scene iii of "Romeo and Juliet".
In line 2, Friar Lawrence says, "Affliction is enamour'd of thy parts." (A. III, s. iii) -- This is an example of personification. In line 3, he then continues by saying, "And thou art wedded to calamity." (A. III, s. iii). This is an example of a hyperbole.In line 5, Romeo says, "What sorrow craves acquaintance at my hand." (A. III, s. iii) which is another example of personification. In addition to these three examples, the entire scene is full of imagery, as is most of Shakespearean plays.