|Miles 1941||C. B. Miles and H. Hunt, J. Phys. Chem. 45, 1346-1359 (1941)|
Heats of Combustion. I. The Heat of Combustion of Acetone
|note old units||On Jan. 1, 1948, it was agreed that energy should be expressed in terms of absolute J, and the denomination "absolute" should be dropped from use. Note that the conversion factor from int. J to abs. J depends on where and when the instruments used to make the measurements were calibrated. The following conversion factors refer to the 'mean int.' units estimated at the Ninth Conference Generale des Poids et Measures in 1948 (see 9th CIPM 1948): 1 'mean int. Ohm' = 1.00049 Ohm, 1 'mean int. V' = 1.00034 V, leading to 1 'mean int. J' = 1.000190 J. However, the conversion factors for the 'US int.' units are 1 'US int. Ohm' = 1.000495 Ohm and 1 'US int. V' = 1.000330 V, leading to 1 'US int. J' = 1.000165 J. Note that Rossini 1930, Rossini 1931, Rossini 1931a, Rossini 1932, etc. uses 1 int. J = 1.0004 abs J from Tech. News Bull. Bur. Stand. No. 156, April 1930 (and 1 cal(15) = 4.185 abs. J, from Int. Crit. Tables 1, p. 24) (see Rossini 1936). However, while still using 1.00040 and 4.1850, Rossini 1934 mentions that the latest determinations at NBS indicate 1 int. J = 1.00032 abs. J. Rossini 1937 starts using 1 cal = 4.1833 int. J (= 4.1850 abs. J).|
1 abs. J = 0.999835 int. J (see Rossini 1952 NBS Circ 500); 1 abs. J = 0.99984 int. J, 1 defined cal = 1 cal(th) = 4.184 abs. J (exactly) = 4.1833 int. J. Also, 1 cal(15) = 4.18580 J = 1.00043021 cal(th), 1 cal(20) = 4.18190 J = 0.999498088 cal(th), 1 cal(mean) = 4.19002 J = 1.00143882 cal(th), 1 cal(IT) (established 1956) = 4.1868 J (exactly) = 1.00066922 cal(th). According to Skuratov 1959, the GOST 8550-57 cal (used in power work) is 1/860 int W-hr = 180/43 int. J (exactly) = 4.18605 int. J, coinciding with the 'int. cal' for steam tables adopted by the Fifth Int. Conf. on the Properties of Water and Stem (London 1956). Also according to Skuratov 1959, in 1934 the Permanent International Thermochemical Comission did not consider it possible to recommend the use of J in thermochemistry, in view of the existence at the time of two electrical system of units (int. and abs.), but believed that the 15 deg cal is the most widespread cal in thermochem and provisionally preserved it as a unit recommending 1 cal(15) = 4.1833 int. J. = 4.1850 abs. J (according to best estimates at the time 1 int. J = 1.00040 abs. J). In later work it became clear that 4.1833 int. J did not correspond to cal(15) (raising the temperature of 1g of pure H2O from 14.5° C to 15.5° C). The Int. Weights and Measur. Committee (CIPM) in 1950 used the critical work of Haas 1950 to define cal(15) and, noting that that actual determinations range from 4.1852 to 4.1858, gave a mean experimental value of 1 cal(15) = 4.1855 +- 0.0005 J. Since 1948 the int. system of electr. units is no longer in use, and all measurements are in abs. units. Skuratov 1959 states that the relation between the two is 1 int. J = 1.00019 abs J (see also Pilipchuk 1959). Note that the defined cal of 4.1840 (abs.) J is a recalculation of the cal adopted in 1934 by the Thermodynamic Commission (1 cal = 4.1833 int. J, apparently introduced by Rossini), which is curious, since it started as 1 cal = 4.1850 abs. J, which became 1 cal = 4.1850/1.00040 int. J = 4.18333 int. J, which then became 1 cal = 4.1833 * 1.000165 abs. J = 4.1840 abs. J.
|note unc||The quoted uncertainty appeared to correspond to one std dev. and was multiplied by 2 to come closer to the desired 95% confidence limit|