1890.] the Validity of Persons Absolute Zero. 1& 



mediate state appears possible ; on the other hand, when we start 

 with a liquid and cool it, it becomes in many cases (see ' Chem. Soc. 

 Trans.,' 1890, p. 340) so viscous that even at 80 to 100 it can 

 scarcely be termed a liquid, and by further cooling it would probably 

 become so firm that it would be regarded as a solid. This affords a 

 striking illustration of what may be meant by the gradual passage of 

 a liquid into a solid, but the solid thus obtained would evidently not 

 be identical with the crystallised solid, nor could it be obtained by 

 heating the crystals from a lower temperature ; as the data on 

 which the calculations are based do not refer to this solid but to the 

 crystalline one, I think it preferable to avoid the use of " critical tem- 

 perature," and to term that given by the equation t the "tern* 



w G 



perature of no crystallisation." 



For the purpose of extending the applications of a law governing 

 the freezing points of solutions which I have lately propounded 

 (' Chem. Soc. Proc.,' 1889, p. 149), it was necessary to determine 

 this temperature in certain cases. The present communication con- 

 tains the details of these determinations, and they afford evidence- 

 that it is not a constant for all bodies, as Person imagined. 



The values which Person obtained with various substances were as- 

 follows : * 



Water -1597t 



Phosphorus 1517 



Sulphur -160-3 



Sodium nitrate 156'7 



Potassium nitrate 170'9 



Hexahydrate of calcium chloride .. 165'3 



Dodecahydrate of sodium phosphate 161'0 



Potassium and sodium nitrate .... 161'0 



The concordance of these values is certainly very striking, espe- 

 cially when the diversity of the substance examined and the difficulties 

 of the determinations are considered ; but a closer examination of the 

 results cannot fail to suggest that the concordance must in some 

 instances have been accidental. The difference between the heat 

 capacities of the liquid and solid, C -c, is often very small, and even 

 ordinary experimental errors in either of the quantities would make a 

 large difference in the results, while in some of Person's determina- 

 tions the experimental errors must have been of more than ordinary 

 magnitude, for these determinations occasionally lasted between one and 

 two hours, during which time the loss by cooling must have been very 



* 'Ann. Chim. Phys.' (3), yol. 21, p. 295 ; vol. 24, p. 129 ; and vol. 27, p. 250. 

 f Taking Person's later determinations of the heat of fusion of water 8CKV 

 (' Ann. Chim. Phys.' (3), yol. 39, p. 73), this value becomes -16l'3. 



