Heretofore unpublished enthalpy data which were used in the derivation of smooth enthalpy and heat-.capacity data for NBS SRM 720 (a-A1, 2 0, heat capacity and enthalpy standard) are presented along with some details of the high-temperature experiments. Recent NBS low-temperature measurements on SRM 720 are smoothed by a least-squares spline technique and a revised table of certified values for enthalpy and heat capacity of a-Al,() from 10 K to near the meltng point (2250 K) is presented.

Laser power and energy measurements are commonly made in calorimeters operating in a constant temperature environment. Calorimeters of this type are analyzed in terms of the first law of thermodynamics and the boundary value problem describing heat flow in the calorimeter. This theory of the measurement suggests design features of the calorimeter, sources of error to be avoided in design and operation, and tests to demonstrate experimentally the adequacy of the design. The analysis shows how time—temperature data can be used to allow for the temperature gradient on the calorimeter and the heat exchange due to transients in the temperature.

Principles and detailed procedures are described for measuring la se r energy and power in terms of e lectrica l e ne rgy based on voltage, resistance , and frequency standards. The construction of a sma ll isoperibol ca lorimetcr used for th e measurements is desc ribed. The ca lorimeter wi ll accommoda te 0.0] to 20.1 and 4 X 10 5 to I W cw and is limit ed to a maximum pul se intens it y of 0.1 .I/cm'. The s tandard deviation of comparison meas urements using two calorimeters and a beam s plitter is 0.08 percent when the s maller energy input is not less than 0. 3 1. The estimated limit s of sys temati c eITor for one ca lorim eter are ± 1.0 percent of the laser e ne rgy mea s ured by the calorimeter.Key words: Calorin1Ptry: la se r: lase r calorimetry: lase r energy measurement; lase r power measurement.

No abstract

An adiabatic calor imeter accur ate t o 0.1 percent and suitable for heat capacity measurements of solids and liq uids over the the temper atur e range 39 0 to 500 0 C is d~scribed . Factors affecting the design and accuracy are di scussed. AutomatIc controls pen mt one-man operaion of the apparatus. Measurements of th.e heat capacity of ~1 203 agree to 0.1 percent with earlier measurements made with other calorI meters at the N atlOnal Bureau of Standard s.