202 abstracts: physics 



small compared with the other quantities of heat which are iisuallj^ 

 observed, but for liquid ammonia in the range — 40 to + 40°C. and 

 corresponding saturated vapor pressures it is sufficiently large to be 

 taken into account in calorimetric determinations of specific heat; and, 

 in consequence, the measurements here described were made as a 

 supplement to a series of such determinations in order to correlate 

 measurements of specific heat of liquid ammonia made at constant 

 pressure with others made under saturation conditions. 



The latent heat of pressure variation has been determined in two 

 ways, namely, by direct calorimetric observations and by computation 

 from the expansivity, using for the latter two independent sources of 

 experimental data. Thus, three independent determinations were 

 obtained. N. S. 0. 



PHYSICS. — Latent heat of vaporization of ammonia. Nathan S. 

 Osborne and Milton S. Van Dusen. Bureau of Standards 

 Scientific Paper No. 315. Pp. 33. 1917. 



Using a calorimeter of the aneroid type specially designed for the 

 peculiar conditions, the latent heat of vaporization of ammonia has 

 been determined throughout the temperature interval -A2 to -52°C. 



A detailed description of the design and construction of the instru- 

 ment has been given in a separate paper.^ The results of each of 34 

 determinations agree with the mean result as expressed by means of an 

 empirical equation within one part in 1000. An empirical equation 

 was found that in addition to representing closely the results in the 

 range of temperature covered experimentally also conforms to what is 

 known about the behavior of substances in general when approaching 

 the critical point. 



As a final result the latent heat of vaporization of ammonia, that is, 

 the heat required to convert saturated liquid into saturated vapor at 

 constant temperature, in joules per gram, is expressed in the range 



-42 to -52°C. by the equationj 



L = 137.91 \/l33 - e - 2.466 (133 - B) 



If the latent heat of vaporization is expressed in calorieS2o per gram, 

 taking 1 calorie2o = 4.183 joules, the equation becomes 

 L = 32.968 a/133"^0 - 0.5895 (133 - d) 



Using the results obtained for the latent heat of vaporization of 

 ammonia together with the specific heat of the saturated liquid, the 

 specific heat of the saturated vapor has been computed for various 

 temperatures and given in a table. N. S. 0. 



» Bulletin of the Bureau of Standards 14: 133; Sci. Paper No. 301. 1917. 



