A peptide synthesis instrument can be used for small scale peptide synthesis. The instrument can include several unique features, including a compression style reaction vessel permitting quick setup of the reaction vessel, a double reaction vessel system permitting efficient mixing without loss of solvent or solvent-to-resin contact, gravity-fed heated reservoirs establishing a fixed volume for delivery to the reaction vessel, fume-free solvent addition permitting solvent addition to fixed bottles, and an improved amino acid manifold assembly which reduces the number of components and increases the ease of use of the instrument. Each of these features improve upon the current state of the art in solid phase automated peptide synthesizers.