SummaryIntra-ocular pressure was measured before and throughout airway establishment with either the laryngeal mask airway or tracheal tube. Similar measurements were made on removal of either airway and the amount of coughing noted in thejrst minute after removal. There was a significantly smaller increase in intra-ocular pressure ( p < 0.001) using the laryngeal mask airway, both on placement and removal, than with the tracheal tube. Postoperative coughing was significantly reduced using the laryngeal mask airway ( p < 0.001). There was a significantly greater rise in heart rate using the tracheal tube ( p < 0.01) probably related to an increased cardiovascular response. The laryngeal mask airway is recommended as an alternative to tracheal intubation in routine and emergency intra-ocular surgery.
The need for more complete data on the vapor pressure and thermodynamic properties of many elementary substances has prompted us to determine the vapor pressure of solid beryllium over a wide temperature range. For these measurements both the Langmuir and Knudsen methods were used and the data obtained by these two methods are in good agreement. Intercomparison of these data affords a means of determining the value of the condensation coefficient for this substance. The theory and use of these methods are described by other investigator^.^,^^^^In Langmuir's method the vapor pressure of a substance is determined by the relationship where m is the rate a t which the material evaporates into a vacuum per unit area of surface, P is the vapor pressure, M is the molecular weight of the evaporating particle, R is the gas constant per mole, T is the absolute temperature and a is the condensation ~oefficient.~ The necessary relationship for determining the vapor pressure of a substance by Knudsen's method iswhere m is the rate at which the vapor under its equilibrium pressure will effuse through an orifice, and the other symbols have the same meaning as before. ExperimentalThe measurements consisted in the measurement of the rate a t which a metal surface evaporates into a vacuum (Langmuir method) and the determination of the rate a t which metal vapor a t its equilibrium pressure effuses through an orifice (Knudsen method). For the former measurements the samples were in the form of either cylinders or annular rings; for the latter the finely divided material was placed inside buckets constructed of sheet molybdenum. The annular rings were approximately 2.8 cm. 0.d. X 1.3 cm. i.d. X 1.0cm. thick; the cylinders were approximately 2.5cm. long X 2.3 cm.diameter. Themolybdenum buckets were approximately 1.9 cm. long X 1.9 cm. diameter andhadeffusion holes0.318cm.and0.398cm. in dia., respectively. Since the solid samples changed size due to evaporation they were measured between runs. The areas were corrected to take into account the increase due to thermal expansion.The beryllium samples used were of two sorts : vacuum(1) This work was carried out under contract between the Office of Naval Research and the Ohio State University Research Foundation. The coefficient, u, is the condensation coefficient-sometimes called the accommodation coefficient; however, since this is ambiguous in that the term has been preempted for the thermal accommodation, we feel that the more descriptive term "condensation coefficient" is preferable. (4a) Johnston and Marshall, ibid., 62, 1382 (1940).cast and experimentally sintered. Both of these materials were used for the Langmuir type measurements whereas for the Knudsen measurements the vacuum cast material was used exclusively. All of the vacuum cast material used was of high purity. The analysis of the material used in the Langmuir runs is A1 0.06%, Cr O.Ol%, Cu O.Ol%, F e 0.07%, Mg O.Ol%, Ni O.Ol%, Si 0.03%, together mth entirely negligible amounts of several other impurities, and Cr O.Ol%, Cu...
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