Notices of the proceedings at the meetings of the members of the Royal Institution of Great Britain with abstracts of the discourses . with itthrough the neck of the calorimeter would still remain gaseous. Butif we were to take liquid nitrogen as the calorimetric substance, air,being heavier than nitrogen but having a higher boiling point, would,in falling down the neck of the calorimeter, come in contact with the 1904.] on Liquid Hydrogen Galorirmtry. 581> cool gaseous nitrogen and be condensed. Hence nitrogen would notbe a convenient calorimetric substance. In any case, the boilingpoints
Notices of the proceedings at the meetings of the members of the Royal Institution of Great Britain with abstracts of the discourses . with itthrough the neck of the calorimeter would still remain gaseous. Butif we were to take liquid nitrogen as the calorimetric substance, air,being heavier than nitrogen but having a higher boiling point, would,in falling down the neck of the calorimeter, come in contact with the 1904.] on Liquid Hydrogen Galorirmtry. 581> cool gaseous nitrogen and be condensed. Hence nitrogen would notbe a convenient calorimetric substance. In any case, the boilingpoints of nitrogen, air, and oxygen being so close together, it isobvious that liquid air is the most convenient substance in theneighbourhood of -180° to -200° C. » The calorimeter has been described in my paper On theScientific Uses of Liquid Air, * and later an improved form in•Recherches sur les Substances Radio-Actives, by Madame Curie,sffurther a sketch of it is given in the paper on The Absorptionand Thermal Evolution of Gases occluded in Charcoal at LowTemperatures. X The annexed diagram shows its construction. It Fig. consists essentially of a large vacuum vessel A, capable of holdingtwo or three litres, into which is inserted the calorimeter, a smallervacuum vessel B, of 25 to 50 capacity, which has been sealed onto a long narrow tube G-, projecting above the mouth of A, and heldin its place by some loosely packed cotton wool. From the side ofthis narrow tube, either before or after passing out of A, a branchtube. E, is taken off to enable the volatilised gas from the calorimeterto be collected in the receiver F, over water, oil, or other suitableliquid. To the extremity of the projecting tube Gr, a small test-tubeC, to contain the portions of material experimented on, is attached bya piece of flexible rubber-tubing D, thus forming a movable joint, * Roy. Inst. Proc. 1894, vol. xiv., p. 398. t 2nd Edition, p. 100. X Roy. Soc. Proc. 1904, vol. lxxiv., p. 123. 58
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