A Dictionary of Applied Physics Volume 1 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1922 edition. Excerpt: ...The specific heat of the fluid must, therefore, be known in order to obtain the latent heat (iv.) Ramsay and Marshall.1--Sir William Ramsay and Miss D. Marshall employed an exceedingly simple and convenient apparatus for the determination of the heat of evaporation of different liquids at their boiling-points. The apparatus consisted essentially of a glass bulb with a heating coil inside. This was surrounded with a jacket of the vapour of the liquid at the boiling-point. The heat necessary for evaporation was supplied electrically, the quantity evaporated being determined by the loss of the weight of the liquid from the bulb. In their experiments they employed a duplicate set of apparatus connected in series, and obtained the latent heat as a ratio from the known value of the one substance taken as standard. This method is such that the procedure enabled the experiment to be carried out without an exact knowledge of the values of the electrical units, except so far as it was necessary to correct for the unequal resistance coils in the two vessels. In using the method at the 1 Phil. Mag., 1896, xli. 38. present day it would probably be preferable to employ a single unit and determine the energy generated in the heating coil with precision electrical instruments. One advantage of the method is that no correction is necessary for heat loss. The apparatus is shown diagrammatically in Fig. 8. The bulb had a fine spiral platinum wire, the ends of which were attached to stout platinum terminals sealed into the glass; the terminals were gilded and amalgamated. The upper end of each bulb was drawn out into a rather narrow open tube through which the liquid could be introduced, and which could be closed to prevent loss during weighing. This bulb...