42 Mr. 8. U. Pickering on the Heat of 



The first point of Dr. Walker's criticism deals with my 

 results with the freezing-points of sulphuric acid and other 

 substances : his conclusions, however, are based on a con- 

 fusion between two very different forms of experimental 

 error — (1) the deviation of the values from the absolute truth, 

 and (2) the relative error of the consecutive determination of 

 a single series performed under strictly identical circum- 

 stances, on which latter the existence of changes of curvature 

 must of course be based. As I have recently dealt at length 

 with these determinations (Ber. cler deutsch. chem. Gesell. xxv. 

 p. 1099), I need not say more about them here beyond men- 

 tioning that although Arrhenius's calculated values agree very 

 well with my observed values as far as a depression of *4°, 

 they do not do so even for this short range within the limits of 

 experimental error, and by no means, therefore, disprove the 

 existence of changes of curvature. 



Dr. Walker's objections to my conclusions as to the 

 irregularities with alcohol solutions fall to the ground when 

 the proper estimate of the experimental error is taken, and if 

 he refers to the Bericlrte, xxiv. p. 14(i9, he will find a pre- 

 liminary notice of results with some 18 other non-electrolytes, 

 which will show r him that alcohol is not the only body belong- 

 ing to this class which I have investigated. In a later number 

 {Ber. xxiv. p. 332t5) he will also find a detailed examination 

 of some results with cane-sugar, wdiich show that even in the 

 case of this body, which the supporters of the gaseous theory 

 of solution take as a typical substance, irregularities are by 

 no means absent*. 



In another paper in the same journal {Ber. xxiv. p. 3317), 

 I have dealt fully with the question of the direction of the 

 deviation of the depression of the freezing-point w^ith increase 

 of strength, and need only remark here that the fact that the 

 direction of the deviation is generally the reverse in the case 

 of electrolytes to what it is in that of non-electrolytes, must 

 render any analogy between these deviations and those of 

 gases from Boyle's law very questionable, even if van 't Hoff's 

 calculations could be applied with any strictness to solutions 

 of finite strength. 



Dr. Walker then reiterates Mr. Shaw's objection to my 

 calling the monohydrate of sulphuric acid and other similar 

 bodies " solvents," but, like Mr. Shaw, he does not help us to 

 appreciate his objections by giving us any definition of the 

 term solvent. These bodies, however, certainly do dissolve 



* Other papers on the cryoscopy of weak solutions are now being 

 published in the Berichte. 



