The present series of measurements of heat capacity and heat of vaporization of water in the range 0° to 100° C have been made to provide greater certainty in the values of the specific heat of water for calorimetric purposes and also to provide greater reliability in the values of enthalpy and the other derived propert ies for use in st eam tables.. To insure the desired accuracy in the specific-heat determinations, complete new calorimetric equipment was designed and built. The same fundamental principles of flu id calorimetry by the electric-heating method were used as in previous measurements extending from 0° to 374° C. In the present case, the limited range of t emperature and press ure allowed greater freedom of design to provide for hi gher accuracy in measurements. Heat leak was accounted for by observation, although it was kept practically nil by insulation and by thermal control of the envelope.Temperature uniformity in the calorimeter was secured by an efficient circulation pump. T emperature uniformity in the envelope was secured by a controllable saturated-steam bath. T emperatures were measured by platinum resistance thermometers supplemented with numerous thermoelements. H eat added was measured electrically. The process of evaporation was closely controlled by manipulation of a sensitive throttle valve.From 256 heat-capacity experiments and 152 vaporization experiments, as finally r educed Rnd formulated, there was obtained a group of properties of water comprising specific heat, enthalpy of both li qu id and vapor, heat of vaporization, and specific volume of saturated vapor in the range 0° to 100° C.The values of specific heat have been compared with values from several important researches by both the mechanical and the electrical method. This comparison shows a more satisfactory accord of the present results with the results of Rowland, of Laby and H ercus, and of Jaeger and von Steinwehr. than with those of Callendar and Barnes.

The completion of new measurements of heat capacity and heat of vaporization of water in the range 0° to 100° C has contributed new data which affect the accepted values of the saturation properties of water and steam in the whole range up to the critical region . With these new data, it is now possible to compile the results of the entire series of measurements which have been carried out in this laboratory into a single table of smoothed values of the properties of saturated water and steam. The compilation presented supersedes the previous tabulations which have accompanied reports of the experimental measurements in this laboratory.The properties of saturated stearn and water included in the tables presented in this compilation are vapor pressure, specific volume, enthalpy, and entropy.In the previous reports [1, 2, 3, 4]1, data obtained by calorimetric measurements have been given in several partial contributions, none of which has covered the entire range 0° to 374° O. It is the purpose of the present compilation to assemble these data into a thermodynamically consistent group, with the experimental irregularities smoothed out by the use of formulations. As far as possible, the formulas used. both empirical and theoretical, are indicated, and the experimental bases of the empirical formulas are also given. The units used are the same as those in the International Steam Tables [9] .It will be convenient to give the descriptions in two mllin parts, the first being for the range 0° to 100° 0 and the second from 100° to 374.15° 0, since most of the reductions in the range 0° to 100° 0 have already been made in the report [4] on the experimental work, which is being published at this time. In that report an account is given of the measurements of the heat capacity and heat of vaporization of water, including the reduction of the data to give values of specific heat, enthalpy of both liquid a, nd vapor, and specific volume of the vapor. The values in this range are taken directly from the report, making conversions to the units used in this tabulation.

A mercury manometer using capacitance sensing of meniscus positions has been refined to give an accuracy within 2 parts in 108 of the pressure in the range from 1 x lo4 to 1.3 x 105 N/ma. The determination of pressure ratios is accurate within 1.5 parts in 1 0 6 for pressures in the same range.

The Intern ationa l Practica l T empera ture Scale of 1948 is a text re vision o f t he Int ernational T emperat ure Scale of 1948, the numerica l values o f t emperat ures r e maining t he sa me. The adj ec tive " Practical" was added to t he na me by t he Intern ational Commi ttee on Weigh ts and M easures . The scale con t inues t o be bascd upon s ix fix ed and r eprodu cible equilibrium t emperatures to which valu es ha ve been ass igned , a nd upon t he sa me in terpolation formulas relating te mpera tures to t he in dica t ions o f specifi ed measuring inst rumen ts . Some cha nges ha ve been ma d e in t he text to m a ke t he scale more re produ cible t han its pred ecessor. The t riple point o f wate r, with t he value 0.01 °C replaces th e form er ice po in t as a defi n ing fix ed poin t of t he scale. It is also r eco mm endcd t hat t he zinc point , wi t h t he value 419. 505 °C, be uscd ins tead of t he sulfur po in t . The recomm end ations include n ew informatio n t hat has beco mc availa ble s in ce 1948.

Calorimetry is the measurement of quantities of heat. Temperature scales are usually involved. The General Conference on Weights and Measures adopted the International Temperature Scale (practical scale) in 1927 and its first revision in 1948. This scale is nearly parallel to the thermodynamic scale, proposed by Kelvin in 1854. In 1954 the General Conference redefined the Kelvin Scale, in the manner which Kelvin originally said “must be adopted ultimately,” by assigning a value for the temperature of a single fixed point, viz. 273.16° for the triple point of water (ice point=273.15°). Several calories have been used in the past but the joule was adopted for the unit of quantity of heat in 1948. The need is stressed for using units of heat which are unambiguous.