Emulsin preparations of high purity were obtained as follows. A water extract of sweet almonds was pptd. with acetone, freed of water by repeated, alternate treatment with acetone and ether, redissolved in water, and pptd. with ZnSO4. The precipitate was again treated alternately with acetone and ether as above, redissolved in 10 parts of water, filtered and subjected to ultrafiltration through a 2.8% acetic acid-collodion membrane under a 300-400 mm. pressure difference. Using salicin, f = k/g where k is the monomolecular constant in hydrolysis of salicin in the neighborhood of zero polarimetric reading and g is the wt. in gms. of solid material in 10 cc. of enzyme solution, a rise in the ratio sal:f. from 0.015 to 11.1 was found, or a 740 fold increase in purity, measured in this way.