Mixter — Formation of Trisodium Orthophosphate. etc. 105 



Heat observed T _._ 10,743° ll,309 c 12,969 c 



" of oxidation of iron... — 48 c — 48 c — 48 c 



« " oxygen absorbed. __ — 58 c — 90 c — 67 c 



10$31 C 1 1,1 7l c 12,854° 



For 1 gram of arsenic 2,127 c 2,234 c 2,132 c 



The mean of the results is 2,168 c and for 150 grams of arsenic 

 it is 325*2 C . The heat of combination of sodium oxide with 

 arsenic pentoxide is derived thus : 



5Na 2 2 -f 2 As = 3Na 2 0,As 2 5 + 2Na 2 + 325-2 



5Na 2 + 50 - 5Na 2 2 + 97-0 



3Na 2 + 2As + 50 = 3Na 2 0, As 2 5 + .__ 422-2 



2As + 50 = As 2 5 219-4 



3Na 2 + As 2 5 = 3Na 2 0, As 2 5 + 202-8 



Two determinations of the heat of union of arsenic pentox- 

 ide with sodium oxide gave for 1 gram of the former 792° and 

 867 c respectively. The combustions were not satisfactory, as a 

 little sodium arsenite was formed. Using the higher result, we 

 have 867x230 = 194,400 c for the heat effect of 3Na 2 + As 2 5 . 

 • The heat of formation of trisodium orthoarsenate is derived 

 as follows : 



3Na„0 + 2 As + 50 = 2Na 3 As0 4 4- . 422-2 



3Na 2 4- 30 = 3Na 2 + 299-4 



2Na 3 , As, 4 = 721-6 C 



Na 3 , As, 4 = 360-8 c 



The heat of formation of trisodium arsenate in solution cal- 

 culated from . Thomsen's heat of neutralization of arsenic acid 

 is 381-3; subtracting 17*7, the heat of solution of Na 3 As0 4 

 (Joly),* gives 363'6 for Na 3 ,As,0 4 . 



Antimony. 



A mixture of pulverized antimony and sodium peroxide 

 does not burn throughout the mass when kindled at one point, 

 hence sulphur or some other substance must be added to the 

 mixture to furnish the heat required to effect the combustion. 

 The following are the experiments : 



1 2 



Antimony _ 10*000 grams 10-000 grams 



Sulphur 1-000 " 1-000 



Sodium peroxide 31 " 30 



Water equivalent of system... 4,028 " 4,222 



Temperature interval 4-384° 4-208° 



*C. R., civ, 1704. 

 Am. Jour Sci.— Fourth Series, Vol. XXVIII, No. 164.— August, 1909. 



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