Continuous Analysis of Ortho-Parahydrogen Mixtures
The ratio of the thermal conductivity of parahydrogen gas to that of normal hydrogen gas (25 percent para) is essentially one from 20° to 40°K, rises sharply to a maximum of about 1.2 near 150°K, then slopes to an approximately constant value of 1.02 at room temperature as the ratio asymptotically approaches one at very high temperatures (Figure 1). Bonhoeffer and Harteck, in 1929, utilized this difference in thermal conductivity for determining the composition of orthoparahydrogen mixtures, and most workers since that time have used one or another modification of the thermal conductivity method. Bonhoeffer and Harteck, and also Farkas, used a single glass cell containing a loop of platinum wire and immersed in liquid air or liquid hydrogen. They measured the actual resistance in ohms of the wire carrying a given current and determined the ortho-para composition of hydrogen in the cell from the resistances. Of particular interest is the fact that by making measurements with mixtures of known composition, Farkas was able to show that an exact linear relation exists between the resistance of the wire and the parahydrogen content.1
KeywordsTungsten Wire Cell Block Wheatstone Bridge Back Pressure Regulator Bridge Current
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- 1.A. Farkas, Orthohydrogen, Parahydrogen and Heavy Hydrogen, Cambridge University Press (1935).Google Scholar