LIII.-Calorimetric Investigations; by R. BUNSEN.* (Continued from page 282.) 2. The Determination of specific heat. 20 The simplest way of obtaining the specific heat of a substance is to determine once for all the amount of heat, expressed in scale divisions, which one gram of water loses in cooling from 1° C. to 0° C., and to divide by the value W, thus formed, the quantity of heat W, measured on the same scale, which one gram of the substance loses for the same difference in temperature. If the weight of the substance is G, its temperature t, the number of corrected divisions which the mercury thread of the scale has advanced T, then the specific heat desired results from the equation S= T (6) in which, for t, the boiling point of water, corresponding to the state of the barometer during the experiment, is to be taken. In order to communicate to substances the constant temperature t, use is made of the apparatus, fig. 4 (p. 173), which is drawn to a scale of of its real size. The tin vessel A, which is provided with a water guage, contains as much water as is necessary in order that, by means of the small gas lamp underneath, a continual jet of steam of 12 hours duration may be produced. The steam enters through the rubber tube a, and the outer glass vessel B into the rubber tube b, which communicates with an ordinary 'condenser. Within the vessel B, which is filled with continually renewed steam, is the heating vessel ƒ, in the form of an ordinary thin walled test-tube whose upper opening is not widened out but somewhat narrowed and cut off sharply. The opening projects several millimeters above the rubber stopper closing the outer vessel B. When the body to be warmed has remained in the vessel f, which is surrounded on all sides by steam, about one hour, then the whole apparatus, through which the steam still flows, is held by means of the cork ring n; the still closed mouth p is on the likewise closed mouth & (fig. 1) of the snow-surrounded calorimeter, the stoppers are rapidly removed, while almost simultaneously, by tilting the heating apparatus B, the heated body is allowed to fall into the water a, fig 1. The time consumed in falling amounts to only a very small fraction of a second, so that the cooling during the same may be considered as vanishingly small. On the bottom of the inner vessel a, fig 1, is contained a small, perfectly moistened plug of loose cotton wool, which, to * Translated for this Journal, with permission of the author, from Poggendorff's Annalen der Physik und Chemie, Bd. cxli, by Dr. G. E. MOORE, of San Francisco. prevent its rising, is twisted around a coiled platinum wire. This cotton answers a double purpose: in the first place it prevents the glass vessel from being injured by the falling in of specifically heavy bodies; then in addition it aids in the removal from the apparatus of the substances which have been used in the experiment. To effect this, a properly bent wire is bored into the cotton, which, with the substance resting upon it, is drawn therewith to the mouth of the tube, the substance is removed and the cotton without being taken out of the vessel is returned by means of the wire to its former place, The principal advantage, which, independent of its great delicacy, the instrument just described possesses over all other calorimetric contrivances is, that the entire heat which the heated body evolves is employed, without any loss, in the ice melting: the weights of the substances which give up their heat to the 0° C. cooled water of the vessel a, fig. 1, is so small compared with the weight of this water, that the temperature can never rise to 4° C. As the water has at this temperature its maximum density, the fluid which warms itself on the bottom of the vessel a can never rise, and is protected from every loss of heat, not employed in ice melting, by a high superincumbent water column at 0° C., whose conducting capacity for heat is vanishingly small. This circumstance may be observed very beautifully on the ice cylinder, when it has been used for 30 to 40 experiments. There is then to be found in the ice, quite far down on the bottom, where the vessel a is rounded off, a hollow space, melted out and filled with water, which possesses the very regular form of a small glass matrass, while the ice cylinder above this part appears throughout its whole extent entirely unaltered. The weight of the substance to be investigated need be, according to the specific heat to be expected, no greater than 0.3 grams, to at most 4 grams. If the substance is a fluid, or if it is subject to alteration by the access of air or water, it is, as in an organic analysis, sealed in the lightest possible glass case, whose weight is determined in weighing the substance. If the substance floats on water, either above or with the enclosing glass case, it is loaded in addition with a likewise weighed spiral of platinum wire, heavy enough to effect the immersion. It would probably be still more convenient to employ in all cases a light, tightly closing platinum vessel. The amount of heat which the glass case and platinum spiral emit is included. in the calculation in the following manner: Let the weight of the glass case be called G,, its temperature t, and the amount of heat, measured in scale divisions, which one gram of the glass of the case emits on cooling from 1° C. to 0° C. Wg, and let the same factors for platinum be denoted by Gp, t and Wp, then equation (6) will be transformed into The constants Wg, Wp and Ww are first to be determined (once for all), W, results with the aid of the equation from the following observations, in which G denotes the weight of platinum employed in the experiment: W, was calculated by the same equation from the following observations conducted on two kinds of glass, by which the weight of glass employed in the experiment is denoted by G, and the elements for the determination of T according to equation (5) are likewise given. W is obtained from the two following experiments by means w of the equation The calculation gives: from experiment 1: Ww=14660 2: W, 14.654 For the explanation of the method already described, I append the results of several determinations conducted on chemically pure substances, whose specific heat has been determined with great accuracy by the previously customary method of mixture. The elements of observation in these experiments are to be found arranged in the following table 4, whose lettering relates to equations (5) and (7). In the following table 5, are to be found the specific heats computed from these values, together with the ones found by Regnault by the method of mixture. It will be seen that the values obtained with the ice calorimeter agree very closely with those obtained by Regnault by means of the method of mixture, but have always been found somewhat smaller. Whether this constant deviation has its origin in the difference in the methods employed can be the less decided from these few experiments as they were conducted, to be sure with the avoidance of all considerable sources of error, but without special care, while I was at the same time occupied in other labors. The following table 6, contains experiments made with several pure elements whose specific heats could not previously be determined. The specific heats and atomic heats calculated therefrom, are arranged together in table 7. t 99 78 C. 99-82 C. 99° 60 C. 99-78 C. 99-78 C. 99-786 C. 99 Temperature communi cated, Duration of the experi-M1-Mo ment, Mo 11 m 1 -0.130 -0.063 -0.160 -0.090 -0.052 -0.120 01 -0.020 -0.037 0.110 -0.130 -0.076 -0.16 before the experiment,| Movements on the scale after the experiment, Oscillation on the scale, Qo-Q1 100-2 Constants, In relation to the material employed in these experiments and the results obtained therewith, the following is to be remarked. The ruthenium was prepared from the perfectly osmium-free so-called iron residues of the mint of St. Petersburg. For this purpose the gray powder was taken, which |