326 ME. W. S. TUCKER ON HEATS OF 



In order to obtain their values of heat of dilution a series of specific heat values 

 must be found for varying concentrations. As all the experiments were to be 

 performed at air temperatures, varying from 15 C. to 20 C., the method of heating 

 was adopted as described above. 



Only a short range of temperature rise was permitted as the specific heat may 

 change rapidly with temperature. For this reason, such heat was supplied as to keep 

 this rise. of temperature to about 5 or 6 C. The time chosen for the heating process 

 was 1000 seconds, for some solutions, but in the case of hydrochloric acid solutions 

 which have a low specific heat at high concentrations, periods of 10, 11, and 12 minutes 

 were employed. 



In order to show the manner in which the observations were taken the full details 

 for hydrochloric acid solutions are given. Eight solutions are taken and are 

 distinguished by numbers, the strongest being solution 1. The acid employed was 

 the purest obtainable, and the more dilute solutions were obtained from the stock 

 solution by adding distilled water. Observations of specific heat determinations were 

 taken from May 15 to June G, 1913, and are quoted in Tables I. and II. 



Some preliminary experiments with concentrated solutions showed that the gas was 

 driven oft' to an appreciable extent when the temperature exceeded air temperature. 

 For this reason the solutions were cooled about 8 below air temperature, so that their 

 mean temperature is about 5 below that of the air. Later experiments show that the 

 specific heat alters very little with temperature for these solutions, hence no appreciable 

 error is introduced into the heats of dilution as calculated from these specific heats. 



Table I., p. 325, shows the relation between the specific heat and the concentration, 

 expressed as molecules per 100 molecules of water, the molecular weight being taken 

 as 36*5. 



The concentration was obtained from density tables supplied by LUNGE and 

 MARCHLEWSKI. The final temperature is corrected for radiation, and the mean 

 temperature of these is nearly that of the solution for the given determination. 



275 c.c. of the acid were employed throughout, and the water equivalent is 42'5 gr. 

 The first three solutions were heated for 600 seconds, the fourth for 660 seconds, arid 

 the remainder for 720 seconds. 



For the purpose of interpolation many attempts were made to get an equation 

 connecting specific heat and concentration. No simple equation appears to satisfy the 

 condition for dilute as well as strong solutions. The author's interest, however, is 

 chiefly in the concentrated solutions, and for solutions whose strengths lie between 

 the limits of 7 '7 and 22 '8 molecules of the solute to 100 molecules of water it was 

 found that an equation of the type sn" = b was suitable, where s and n are specific 

 heat and concentration respectively, while a and b are constants. 



In the case of hydrogen chloride the equation takes the simple form 



,m'"= 1-277. 



