No abstract

In a paper dealing with the rate of absorption of water by rubber Andrews and Johnston' showed that the observations on a series of sheets of different thickness of the same rubber compound follow practically a single curve2 when the fractional saturation of the sheet as a whole-as determined by the increase in weight on immersion-is plotted against t/a2, t being the period of immersion in water, and a the half-thickness of the sheet. It was recognized that rubber is not the ideal substance for such a test of the general theory which leads to this conclusion, because of the oxidative and other changes which it might well undergo during the long period of immersion necessary; so we looked round for other materials, readily obtainable in uniform sheets of different thickness, which would be more stable under the conditions of experiment, and concluded to try cellulose acetate, celluloid and clear Bakelite (yellow and brown).$ We found however that the sheets of cellulose acetate reach substantial saturation in a few minutes, so rapidly indeed that a very thin sheet would promise to be useful as the absorptive member in a hygrometer; further that the celluloid sheets yielded in time to the water in which they were immersed so much of the original solvent or of camphor that conclusions based upon change of weight of the immersed sheets would be quite meaningless. The sheets of yellow Bakelite (presumably therefore those which in the course of manufacture were cured a t a lower temperature or for a shorter time) upon immersion increased in weight for about two days, but thereafter lost steadily for upwards of two years, the final weight being about 1 7~ less than the original dry weight; corresponding to this, phenol diffused out into the water and was easily recognisable. There remained therefore as satisfactory material for our purpose only the brown Bakelite, sheets of which showed a regular increase of weight throughout the period of immersion; but even with this material we found, when at the conclusion of the experiments the sheets were dried for three days at I I O O (by which time the weight had become practically constant), that the final dry weight was less than the original weight by an amount averaging about 1 7~. This difference may be due, in part or wholly, to the fact that the samples were not so thoroughly dried before the initial weighing; to this loss of material of the sheets may be attributed the fact that the points for the thicker sheets corresponding to the very longest periods of immersion lie slightly below the 1 Andrews and Johnston: J. Am. Chem. SOC., 46, 640 (1924); see also Boggs and Blake: Ind. Eng. Chem., 18,224 (1926); Lowry and Kohman: J. Phys. Chem., 31,23 (1927).2 Immediately after immersion, and until the water, entering from either surface of the sheet, reaches its central plane, the rate of absorption is, of course, dependent on the area but not upon the thickness of the sheet. 8 For sheets of these materials we are indebted to the Eastman Kodak Company, the DuPont Company, and t...

<p>Vat photopolymerization 3D printing provides new</p><p>opportunities for the fabrication of tissue scaffolds and medical</p><p>devices. However, it usually requires the use of organic solvents or</p><p>diluents to dissolve the solid photoinitators, making this process</p><p>environmentally unfriendly, and not optimal for biomedical</p><p>applications. Here, we report biodegradable liquid polymeric</p><p>photoinitiators for solvent-free 3D printing of biodegradable polymeric</p><p>materials by digital light processing. These photoinitiators enable</p><p>systematic investigation of structure-property relationship of 3D</p><p>printing polymeric materials without the interference from the reactive</p><p>diluents and offer new perspectives for the solvent-free 3D additive</p><p>manufacturing of bioresorbable medical implants as well as other</p><p>functional devices.</p>

Available data on the conductance of barium hydroxide solutions are rather limited. Those given in the "International Critical Tables ''1 apply to quite dilute solutions and include only three values which fall within the concentration range 0.016 to 0.20 M. The only other data found in the literature, but not used in deriving the values in the "International Critical Tables," are those of the Bureau of Standards, at temperatures between 23 and 27°.2 However, when these two sets of values were compared, a large discrepancy was found. This observation led us to undertake the present measurements, required for biological experiments at 28°.3 Table I Concentration, miili-equivalents per liter solution, c Specific conductance, k X 10* Equivalent conductance, (k X 10*)/c Concentration, milli-equivalents per liter solution c Specific conductance, k X 10*