324 



MR. W. S. TUCKER ON HEATS OF 



instruments employed showed an accuracy to within 0'02 of a volt or ampere almost 

 throughout their whole scale. The heating coil was of about 0'9 ohm resistance, and 

 such a current was employed as to give readings nearly at the middle of the scales in 

 each instrument. The steadiness of the current was determined by the condition 

 of the secondary cells employed. Such variations as there were, however, were 

 eliminated by readings of each instrument during each minute of heating. 



To find the Thermal Capacity of the. Apparatus. 

 One typical set of observations may be quoted. 



May 8, 1913. 



250 gr. of water were heated for 940 seconds, and the following readings of voltmeter 

 and ammeter were taken alternately at minute intervals. 



Corrected Readings. 



The mean value of the current is 2'925 amperes and of the P.D. 2'582 volts. The 

 heat supplied is 169G'4 calories. Initial temperature 15'37 C. Final temperature 

 21-22 C. 



The mean radiation at the final temperature is 0'0072 G. per minute, and the 

 correction for the whole period 0'06 C. 



Hence, the corrected temperature rise is 5'91 -C., and the water absorbs 1477 - 5 

 calories. The heat absorbed by the apparatus is thus 218 '9 calories, giving a water 

 equivalent of 37 '0 gr. 



For 275 gr. of water, the water equivalent was found to be 42 '5 gr. When the 

 mixing pipettes were employed, values of 4475 and 4 5 '6 gr. were obtained 

 respectively. 



(3) DETAILED OBSERVATIONS FOR HYDROCHLORIC ACID SOLUTIONS. 



1. Experiments at Air Temperature. 



Four typical strong solutions were studied : Hydrochloric acid, lithium chloride, 

 sodium hydroxide, and calcium chloride. 



