CONTENTS I . Acknowledgment ........................................... 4 I1 . Levulose Solutions ........................................ 5 I11 . Description of Apparatus .................................. 8 a The Cells ........................................... 8 b Deposition of Membranes ......................... 1 0 c Recovery of Old Cells .............................. 1 1 d Manometers ........................................ 1 2 e Regulation of Temperature ........................ 16 IV . Measurements ............................................. 19 V . Discussion of Tables ...................................... 3 6 V1 . Conclusions ................................................ 39 V11 . Biography ................................................. 4 0 I. ACKNOWLEDGMENT. Th6 author is glad to avail himself of this opportunity to express his appreciation to Prof. Morse, the late Prof. Jones, Dr. Lovelace, Dr. Reid, Dr. Frazer, Dr. Holland, and Dr. Schwartz for their valuable instruction. The author is especially grateful to Prof. Morse, at whose suggestion and unde w hose guidance this investigation was undertaken and carried out. The author is under obligation to Dr. - Holland for much valuable advice and assistance. The author is indebted to Dr. Frazer for much inspiration, and for his kindly interest in the work. THE OSMOTIC PRESSURE MEASURMENTS OF LEVULOSE SOLUTIONS AT THIRTY DEGREES 11. LEVULOSE SOLUTIONS. The levulose, which was used in this investigation was obtained in Germany. The preliminary purification in which the penta-acetate was made, giving the pure sugar upon hydrolysis, was performed by Dr. C. S. Hudson, of the Bureau of Chemistry at Washington, D. C. The author wishes to acknowledge his obligation to Dr. Hudson and his co-workers for this valuable material. There remained in the sugar some traces of acetic acid. Our solute was freed from the traces of acetic acid by the following method, depending upon the fact that levulose is practically insoluble in cold absolute alcohol. One hundred grams of the once recrystallized sugar were dissolved in fifty cubic centimeters of 75 alcohol which had been previously warmed on a steam bath. Seventy-five cubic centimeters of absolute alcohol were added to this solution. It was necessary, in some cases, to add a little animal charcoal and a few cubic centimeters of washed alumina to remove a slight turbidity. After filtering the mixture, twenty-five cubic centimeters of absolute alcohol were added to the clear filtrate. Upon seeding the solution, the sugar was precipitated. The crystallization was carried on in a dessicator with frequent stirring. The yield was about 50 of the original material used and the specific rotation was found to be 92O. 0, the same value as the one assigned to pure levulose by the Bureau of Chemistry at Washington. Solutions of levulose are peculiar in that they exhibit a change in specific rotation with change in temperature. A solution which is taken from a cell after having given - . --. ... a-. . - . , ljzvulose Solutions. a measurement, is examined in a saccharimeter to determine whether or not it has undergone a change in concentration...