its Atomic Weight and Specific Heat. 41 



of-calcium drying-tower, as shown in the diagram. Although 

 the larger "bulb" of the thermometer is full of spirit, the 

 lower one and the stem are full of mercury, and connected 

 with a fine capillary tube carefully graduated in millimetres, 

 and calibrated. The arrangement constitutes an exceedingly 

 delicate spirit-thermometer, with a mercury index. 



When it is desired to compare a solid element with silver, 

 in order to fix the atomic weight, it is necessary to make a 

 preliminary experiment with the standard metal. For this 

 purpose one cubic centimetre of distilled water is placed in the 

 test-tube, which is immersed in the bulb of the thermometer ; 

 and when the temperature has been equalized, and the thread 

 of mercury has reached a suitable position in the stem, a piece 

 of pure silver weighing 108 centigrammes, and heated to 100° 

 C. in steam, is rapidly dropped into the cubic centimetre of 

 water, and the expansion caused in a given time carefully 

 noted*. According to the law above stated, a centigramme 

 atom, if I may use the term, of any other metal than silver, 

 ought to cause exactly the same expansion when the experi- 

 ment is made with it under precisely the same conditions; and 

 these conditions are very easily realized. I have ascertained 

 that such is the case ; and the approximate equality in " atomic 

 heat " of many of the metals has thus been easily demonstrated. 



The comparison of glucinum with silver was made on this 

 plan ; and it was found that the weight of glucinum which 

 contains nearly the same quantity of heat at 100° C. as 108 

 centigrammes of silver at the same temperature is not 4*6 or 

 4*6 x 3, but 4*6 x 2, or 9*2 centigrammes. 



The " atomic heat " of silver, or the product of the specific 

 heat ( = '05701 according to Regnault) into the atomic weight 

 ( = 108), is 6*157. Using this number as the standard for 

 reference, the experimental number found for the atomic heat 

 of the specimen of glucinum operated with is 5*91. Thus : — 



Atomic heat of silver . . =6*157 

 Atomic heat of glucinum . =5*910 



The difference is less than the known difference between the 

 atomic heat of silver and that of aluminum ; but I am inclined 

 to think that the lower number found for the glucinum used 

 is due to the presence of a little platinum in the specimen of 

 metal. Owing to the high atomic weight of platinum ( e= 197*1) 

 as compared with that of glucinum (9*2), the presence of even 

 a small quantity of the former metal must very sensibly affect 

 the determination of the atomic heat of glucinum. I hope 



* The apparatus is carefully protected from the influence of air-currents 

 during an experiment. 



