8 Notes to preceding Table. 1 The number for beryllium is that calculated by L. Meyer from the data of Nilson and Pettersson : for fuller discussion of specific heat of beryllium see par. 28, pp. 58, 59. 2, 3, 4 Spec. heats of boron, carbon and silicon are discussed on pp. 59–61, par. 29. 5 The higher temperature (+10°) is not given in Regnault's paper, but judging from the context it appears to be approximately correct. 6 This number for chromium is probably too low; see Kopp, Annalen, Supplbd. 3. 77 (note). 7 The specimen of manganese employed contained a little silicon. Spec. heat of molten gallium between 109° and 119°= '0802. (Berthelot, Bull. Soc. Chim. 31. 229.) Spec. heat of amorphous selenion determined at high temperatures is ab. normal, because of large quantity of heat absorbed before fusion. 10 Spec. heat of zirconium calculated by Mixter and Dana from determinations made with sample containing known quantities of aluminium. 11 The specimen of molybdenum employed contained carbon. 19 Spec. heat of gold is nearly constant from oo to 600°; at 900° sp. ht.='0345; and at 1000°= '0352. [Violle, Compt. rend. 89. 702.] 13 Spec. heat of liquid mercury at 55° = '033 (Regnault). The numbers marked with I are probably too large; see Weber's papers referred to below. 9 The names of the various observers are abbreviated in the table: Ann. Chim. Phys. [2] 73. 5: [3] 1. 129: 9. 322 : 26. 261: 38. 129: 46. 257: 63. 5: and 67. 427. Annalen 126. 362: and Supplbd. 3. 1 and 289. lation in Phil. Mag. (4) 49. 161 and 276.] lation in Phil. Mag. (5) 3. 109). 26. The preceding table contains the names of 49 elements, the specific heats of which have been directly determined. For eleven of the remaining elements values have been obtained which are regarded by some chemists as representing the specific heats of these elements : the method employed is based on the assumption that the molecular heat' of a solid compound is equal to the sum of the atomic heats of its constituent elements. (See Kopp, Annalen, Supplb. 3. 321-339.) Thus Kopp found the mean molecular heat' of metallic sulphides of the form RS to be equal to 12: the atomic heat of sulphur is 5-7 ; but 12 – 5*7 = 6-5, which number is regarded as the value of the atomic heat of any one of the metals R. The mean value of the atomic heats of these metals found by direct experiment is 64. Kopp has applied this indirect method to calculate the atomic heats of various elements with which direct experiments could not be made. Chlorine : molecular heats of metallic haloid salts: RCI = 128 RBr=139 RI =134 ............RI,= 19*4. Now as (1) the atomic heat of each of the metals R is about 6:4; (2) the atomic heat of solid bromine and iodine is about 6:6; (3) the chlorides, bromides and iodides examined are chemically analogous; and (4) the molecular heats of the analogous salts are nearly the same, Kopp concludes that the atomic heat of solid chlorine is about 6:4. I2I RCI (128)-R (64)=64 : RCI, (185) - R (64)=12'1, and =6'05. 2 A further argument in favour of this conclusion is afforded by these data, molecular heat of KCIO, =24:8 KASO,=253, hence the atomic heats of arsenic and chlorine are probably 1 By molecular heat is to be understood the product obtained by multiplying the specific heat of a compound into the quantity expressed by the generally accepted formula of that compound; the expression formula-weight will be employed to signify this amount of any compound. ? For detailed data see Kopp, loc. cit. p. 293. nearly the same; but the atomic heat of arsenic is 6'1, therefore the atomic heat of solid chlorine is probably about 6'1. Fluorine : molecular heat of CaF2=16:4 atomic heat of Ca=6.8, hence atomic heat of fluorine = 164-68 = 4:8. = 2 Nitrogen: molecular heats of various more or less analogous compounds : RCIO,= 24.8 RCO3=20°7 RPO,=221 RNO,= 230. Hence, it is argued, the atomic heat of solid nitrogen is probably rather less than that of chlorine or arsenic (about 6), somewhat greater than that of carbon or silicon (about 5:2), and nearly equal to that of phosphorus (about 5:8); therefore the value of the atomic heat of solid nitrogen probably lies between 5'5 and 5.8. Oxygen : the molecular heats of metallic oxides are, as a rule, rather less than those of corresponding haloid salts; therefore the atomic heat of solid oxygen is probably less than 6; thus RO = II'I...... RCI = 128 RBr=139 RI =134, : ..................RI,= 19*4. Further data for finding the value sought for are these, molecular heats...... R,09=27'2; KAsOz=25*3 ; KCIO,= 26*3 ; KMn0=28.3. The values deduced for the atomic heat of solid oxygen are, from RO ...4:6, from KASO3...4'2 RO2...37, KCIO4...3.5 (assuming Cl=6] „ R,O3...4:8, + KMnO,..3-8, hence the mean value is 4'1. Hydrogen : the principal data are these, molecular heat of ice (H,0)=9 : molecular heat of Cu,0=156. Hence, it is argued, the atomic heat of solid hydrogen is 15.6 - 9 probably less than that of copper by the amount = 3:3 : 2 = land = 23. but atomic heat of copper = 6:4, therefore the atomic heat of 4 solid hydrogen=3'1. Molecular heat of NH Cl=20 : Sbut atomic heat of N1 is about 5-67 Cl 6:45 Now 20– 12 = 8, and 4 = 2, therefore the atomic heat of hydrogen is about 2. Molecular heat of NH.NO,=36-41 oxides R,03=27'21* Hence 364 - 27*2 = 92, and 92 4 The mean of these three results is 2'4, which may perhaps be taken to represent the atomic heat of solid hydrogen: the method of calculation however involves many assumptions and the use of numbers themselves obtained by indirect means. From experiments with palladium charged with hydrogen, Beketoff deduced the number 5'9 as representing the atomic heat of solid hydrogen". The molecular heats of the oxides, chlorides, carbonates, nitrates, and sulphates of calcium, barium, and strontium are nearly the same as the molecular heats of the corresponding salts of metals the atomic heats of which have been directly determined, and found to be represented by the mean number 64; hence the atomic heats of calcium, barium, and strontium are probably represented by a number approximately equal to 6:4. The agreement noticed between the values of the molecular heats of the chloride and carbonate of rubidium, of the oxides and chlorides of chromium and titanium, and of the oxides of vanadium and sirconium, and the molecular heats of corresponding salts of other metals which themselves exhibit the mean atomic heat 6:4, shews that the atomic heat of rubidium, titanium, zirconium, chromium and vanadium is probably about 6:48 (see notes 6 and 10 to table of specific heats of elements, p. 50). 1 Indirectly determined, see p. 51 and p. 52. 3 For a full collection of specific heat data see F. W. Clarke's Constants of Nature, part 11: or, Landolt and Börnstein's Physikalisch-chemische Tabellen. Molecular heat, heat. The following numbers representing molecular heats of salts of recently discovered elements are given by Nilson (Ber. 13. 1459 et seq.). Specific Temperature. Scandium salts (Sc=44'03) Sc,03 0'153 0° - 100° 20-81 Sc,.350 0 1639 Erbium salts (Er=166) Er,0, o'o65 247 Erg. 3504 O'104 64'5 Yttrium salts (Y=8985) Y,0 O'1026 23:3 Y,.350 0'1319 61.6 Ytterbium salts (Yb=173) Yb203 O‘0646 25.5 Ybz: 3504 Oʻ104 65.8 62.42 Gallium oxide Ga,03 Oʻ1062 19'5 222 If we assume that the atomic heat of oxygen is 4:1 (see p. 52), and regard only the oxides in the above table, then the following values are found for the atomic heats of the metals, Sc=4'2 Er=6*1 Y=5'5 Yb=66: 6 Ga=36 In=5'0. If a similar process is applied to the sulphates (atomic heat of S= 6), then the atomic heats of the metals are all represented by negative numbers; hence either (1) the value of the atomic heat of oxygen in compounds is not constant, or (2) that of sulphur varies, or (3) that of the metals Sc, Er, Y, Yb, Ga, In, is negative in their sulphates, and, for some of these metals, is abnormal in their oxides. The last hypothesis can scarcely be adopted. Indeed if the atomic heats of gallium and indium as determined by direct experiment are placed beside the numbers obtained by calculation from the molecular heats of the oxides (assuming O = 4'1) we have this result: Directly Calculated from determined. Atomic heat of Gallium 54 Indium oxides. 6.5 36 50 We can scarcely hesitate which numbers to prefer. |