500 M. llegnault on the Specific Heat of Simple Bodies, 



of sodium which had been used for the experiments Nos. I. and 

 II. To this end, immediately on taking the sodium out of the 

 naphtha, the tinfoil was unfolded and rapidly wiped dry with 

 tissue-paper, as also was the metal itself, and the cylinder imme- 

 diately replaced in the tube surrounded by the cooling mixture. 

 The experiments Nos. III. and IV. are less precise than Nos. I. 

 and II. ; first, because the metal had undergone a more profound 

 alteration in contact with the air, and then because the tempera- 

 ture of the cooling mixture having begun to ascend, the thermo- 

 meter at the moment of the experiment only marked a relative 

 minimum, which did not continue, and which ap})lied less exactly 

 to the whole mass of the metal than the absolute and stationary 

 minimum at which the determinations Nos. I. and III. had been 

 made. It is hence better to take only the mean between Nos. I. 

 and III., which would give for the specific heat of metallic sodium 

 0-2934. 



The product of this specific heat by the atomic weight 287*2, 

 which chemists assign to this metal, is 84*2 ; but the product 

 by 143-6, the half of this atomic weight, is 42*1. This latter 

 product alone is comprised within the limits which we have recog- 

 nized for other simple bodies. It is therefore evident that the 

 atomic weight of sodium is 143-6, and that the formula of soda 

 ought to be written Na^O, and not NaO. 



It is assumed that the fusing-point of sodium is about 90**. 

 I wished to determine it with accuracy. I poured melted sodium 

 into a large glass tube, dipped in the melted metal a mercurial 

 thermometer, and observed the course of its cooling. In many 

 experiments the thermometer became stationary at a temperature 

 which, corrected for that portion of the column which was not 

 plunged in the metal, corresponded precisely to 97°-63. The 

 stationary temperature observed during the cooling is therefore 

 97°'63, and it is the only element of this kind susceptible of an 

 accurate determination. 



Potassium. 



I have not thought it necessary to make new determinations 

 of the specific heat of potassium ; the experiments already on 

 record {Ann. de Chim. et de Phys. 3 id series, vol. xxvi. p. 266) 

 are sufiicient for the conclusions which may be drawn as to the 

 atomic weight of this metal. As potassium undergoes a gradual 

 softening with the temperature, its specific heat experiences a 

 material increase, and its value may be found perceptibly too 

 great. But I have made some experiments for determining 

 exactly its fusing-point, which treatises of chemistry generally 

 place at about 55 degrees. 



Potassium prepared by M. Rousseau was melted in a large 

 glass tube under naphtha. After the solidification of the metal. 



