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January 1969


Arch Ophthalmol. 1969;81(1):150. doi:10.1001/archopht.1969.00990010152029

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To the Editor.  —Recent work, both at a clinical and at an experimental level, has revealed the superiority of nitrous oxide gas over carbon dioxide gas when used in a Joule-Thomson cryoprobe. The boiling point of nitrous oxide is -88.46 C as compared to carbon dioxide which has a boiling point of only -78.5 C. Also, the freezing temperature of nitrous oxide is -90.81 C as compared to -56.6 C for carbon dioxide, which is also its triple point (solid carbon dioxide starts forming below this temperature).Therefore, not only is a maximum operational temperature or lower than -80 C possible but more precise control of the instrument can be obtained by reducing the gas pressure from 750 psi to 600 psi, as no solid is formed. This allows the probe tip temperature to be varied accurately from -40 C to below -80 C.

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