OF ARTS AND SCIENCES. 207 



precipitate formed by the 4.8 mol. A previous experiment, made by 

 adding KOn iu the calorimeter to the liquid jiortiou of the mixture 

 1 alum -[- y KOII (the precipitate being removed), gave zero for a 



result. 



Series II. 



In the second series of experiments the same quantity of alum was 

 dissolved, 10 mol. KOH added, and the whole made up to 500 c.c, 

 as in Series I. To this was added in the calorimeter 500 c c. of sul- 

 phuric acid solution, containing of H.iSO^ quantities varying from .5 

 to 3 molecules. The numerical data are recorded iu Table II. It 

 will be seen that the rate of heat disturbance per molecule of H.,SO^ 

 is practically constant for n = .5 and n = .75, but increases at n = 1 ; 

 the first precipitation by neutralization of KOII occurs between ?z = .75 

 and ra = 1. The rate then increases to n = 2.2, when it again drops. 

 Instead of expressing these direct results graphically, I have calculated 

 from them (at least from Exp. 42-48) the corresponding points in the 

 Lines I. and III. The possibility of this calculation will be apparent 

 from considering that JI iu Series II. is the formation heat of potassic 

 sulphate plus or minus the heat disturbance involved in separating the 

 equivalent potassic hydrate from whatever form of combination it may 

 be in before the addition of sulphuric acid. If we assume that the 

 n mol. H^SO^ (fi-om n = 1.5 to n =z 2.2) are converted into K^SO^, 

 and count the formation heat of the latter as a known quantity, we 

 have the means of calculating indirectly the values of i/ in Series I. 

 for X = 6, 7, and 10. These values locate the supplementary Lines 

 II. and IV., Plate I. They are separated by a small and approxi- 

 mately constant quantity from the Lines I. and IIL 



A similar discussion of the values for ?i = .5 and .75 will make 

 evident whether or not the addition of KOII beyond 8.13 mol. has 

 any effect. The formation heat of K.^SO, is according to Thonisen 

 31.288 Cal. One half of this, 15.644 Cal., is larger by .96 than the 

 mean result of Exp. 36-39, Series II., which would indicate that heat 

 was absorbed in liberating KOII from its previous state of combina- 

 tion, and hence that the combination of the 0th and 10th mol. in 

 Series I. was accompanied by heat evolution. This, if true, would be 

 an interesting fact ; but the question arises, May not the formation 

 heat of K.SO, in Exp. 36-39 be less than 31.288 Cal., this value 

 having been determined for a degree of concentration six times as 

 great? I therefore determined it independently, using, first, the same 

 quantities of KOII and 11,80^ as occur in the reaction ?? = .5, and 



