A bomb calorimeter and associated apparatus to determine the heats of combustion of organic substances is described. It hEs been employed to obtain the heat of formation of monohydrate citric acid. The value found was AH; = 1837.6 abs. W/mole, = 439.2 kcal/mole.A bomb calorimeter and associated apparatus has been designed and constructed to determine the heats of combustion of organic substances. The calorimeter was calibrated by burning benzoic acid, and has been employed to determine the heat of combustion of monohydrate citric acid. Thermodynamic data for citric acid are of biochemical interest in connexion with the energy changes of metabolic processes. The free energy of formation of the aqueous citrate 3-ion has been evaluated with the aid of biochemical data to be -279 kcal/mole at 25O.1 This is consistent with the previously available combustion measurements for the crystalline monohydrate 2 and data for the solution,3 and ionization 4 only if the entropy has the unlikely value of 88 cal/mole deg. at 25". The combustion measurements in this paper are consistent with a more reasonable value for the entropy of about 70 cal/mole deg. for the crystalline monohydrate.
In a study of the technology of the melt spinning of 6.6 nylon filaments of diameter in the range 30–100 μ, some new crystallisation phenomena have been noted. Because of the geometrical form of the filaments, cooling from the melt is extremely rapid. Solidification takes place in a fraction of a second, and further cooling to room temperature is also rapid. The polymer can be observed at various stages during its quenching, either by taking samples from the running filaments, or by examining it whilst it is running.
Under these conditions, the solid polymer is seen to have a structure not very different from that of the melt. This structure is stable at room temperature for long periods in the absence of moisture. However, on exposure to moisture, diffusion of water into the filament may result in elongation with accompanying changes in the crystalline character. The effects of temperature and moisture concentration on the diffusion process have been studied. X‐Ray diffraction, depolarisation of light and microscopical techniques have been used to examine the crystallisation process in the filament as it is being spun and during the subsequent process of equilibration with water.
X‐Ray and optical results show changes of structure to occur on different time scales: the implications of this on the concepts of polymer morphology are discussed. The important röle played by atmospheric moisture in the crystallisation of 6.6 nylon is established, and the likely dependence on water content of second‐order transition data is examined.
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