From the average results of these seven series of experiments the following values for the specific heat of graphite are deduced: Graphite, therefore behaves in a manner exactly analogous with diamond; its specific heat notably increases with increasing temperature. This increase shows an acceleration from -50° to 0°; from 0° to 250° it diminishes. The curve of the specific heat of graphite shows, therefore, a turning-point in the neighAy bourhood of 0°. The small change in the value of when T AT is about 0°, makes it evident that great care must be exercised = in experiments performed with the object of determining the exact temperature at which this point occurs. The steady de Ay crease from 0° to 250° in the value of AT makes it almost certain that the specific heat of graphite, as that of diamond, is expressed by a constant number at higher temperatures. Inasmuch as it appears that, in the curves expressing the specific heats of diamond and of graphite, the value of the difference yr (graphite) -yr (diamond) becomes smaller and smaller as T increases (within the interval T +50° to T=250°); and as a series of other elements exhibits the same specific heats in all their modifications, it is probable that the constant values which express the specific heats of diamond and graphite at high temperatures are identical. A determination of the specific heat of graphite for the temperatures 500° to 1000° has completely fulfilled both of these expectations: the following Tables give the results of this determination. b. Experiments at High Temperatures with the double Calorimeter. These results may be reduced for an equal temperatureinterval: we adopt the mean of all the lower values, namely 22.2. As the specific heat of graphite at 22°-2 =0·169, the following results are obtained: Phil. Mag. S. 4. Vol. 49. No. 325. April 1875. U For the calculation of this y-value it is assumed that the sp cific heat of graphite, within the temperature-intervals 550° 750°, 750° to 900°, and 900° to 1050°, changes linearly wi the temperature; it is therefore allowable to write Y977-9=0·4670. A comparison of these numbers with those deduced for di mond, viz. 606-7=0·4408, Y806-5=0·4489, 1985-0=0.4589, leads to the following conclusions: (1) The increase of the specific heat with the temperatu Ay whether the values of for graphite and diamond, really i crease within the temperature-interval 600° to 1000°, a whether the values are different for graphite and diamond, cannot with certainty decide. An experimental error in t direct determination of WT, amounting to 1 per cent. too mu or too little, would influence the value assigned to y so as Ay falsify the true value of the quotient as much as 100 As the differences between the above four values of amount at the most to 50 per cent. of the value of this expressio and as the magnitude of WT is not determined to within l To Ay than per cent. of its value, the magnitude of AT may very w be independent of the temperature from 600° and upwards; a the value of this expression may be exactly the same for bo modifications of carbon. Inasmuch, however, as the expe mental methods were not delicate enough to determine this question with precision, it is safer to deduce from the foregoing results the following generalization only-that, from a red heat upwards, the specific heat of carbon does not vary more than the specific heats of those elements which fulfil the law of Dulong and Petit. Thus Bedé* shows that the specific heats of the following elements for the temperatures T are (2) The specific heats of graphite and diamond are identical from the temperature 600° and upwards (there are slight divergencies, but they do not exceed to 2 per cent. of the value of y). By reducing, by the help of the mean differential quotient Ay =0000656, the above values for the specific heat of graAT phite to the temperatures 606° 7, 806°5, and 985°.0, and comparing these with the specific heat of diamond at the same temperatures, we obtain the numbers Although the small difference increases with an increasing temperature, nevertheless it is not greater than the difference between the specific heats of different modifications of other elements. Thus, according to Regnault, the mean specific heats between 10° and 100° for steel and copper are Soft steel =0·1165 Soft copper =0.0948 These differences may be accounted for by the varying molecular aggregation of the substances; and it may be accepted as true that from a red heat and upwards there is no real difference between the specific heat of the graphitic and that of the diamond modification of carbon. Inasmuch as this result appears to me one of great importance, both as regards the specific heat of the elements in general and that of the modifications of carbon in particular, I have sought to answer the question as to the difference or identity of the specific heats of graphite and diamond in another and somewhat simpler manner. On the supposition that the specific heats of graphite and dia * Mém. Cour. de l'Acad. de Brux. vol. xxvii.' |