104 Mixter — Formation of Trisodium Orthophosphate, etc. 



the reaction is more complete than without the inner cup, as 

 was the case in the second experiment. Using the first result 

 we have 



5Na 2 '0 2 + 2P(8166 X 62) = 3N"a 9 0,P 9 B + 2Na 2 + 506,292 c 



5Na 9 + 50 = 5Na„0 2 4- 97,000°* 



3Na 2 4- 2P 4- 50 = 3Na 2 0,P 2 5 + 603,292° 



2P + 50 = P a B + 369,900° 



3Na 2 4- P 2 6 = 3Na 2 0, P 2 5 + 233,392° 



In the Physikalisch-Chemischen Tabellen with reference to 

 Berthelotf 3Na,P,40 = 452*4°, from which is derived 235*5° 

 for the heat effect of Na 2 04-P 2 5 . Berthelotj; and Thomsen 

 both found the heat of neutralization of phosphoric acid by 

 sodium hydroxide to be 34'0. From this we derive Na,P,0 4 ,- 

 Aq = 469-5°. Joly§ gives the following: ]STa,P0 8 24HO = 

 -14-5° and Na 3 PO' 8 + 24BO =+48-1°. (O = 8.) The heat of 

 solution of Na 3 P0 4 is the sum of these numbers, i. e., 33*6°. 

 The experimental data are not given and the writer does not 

 understand the result, which is apparently twice too high. 

 Subtracting one-half of it, 16-8°, from 469*5° we have Na 3 ,P,0 4 

 = 452*7 C , which is essentially the same as given in the Physi- 

 kalisch-Chemischen Tabellen, as stated above. 



From the result of experiment 1 we have 



3Na 2 + 2P 4- 50 = 2Na 3 P0 4 + _. 603-3° 



6Na 4- 30 = 3Na 2 4- (99-8 X 3) + 299*4° 



2(3Na 4- P + 40) = . 902-7° 



3Na 4- P 4- 40 = 451*4 C 



The heat of formation of sodium phosphate found by the 

 two methods is 452*7 C and 451*4°, and hence the heat of combi- 

 nation of sodium oxide with phosphorus pentoxide obtained 

 by the different methods is, essentially, the same. 



Trisodium Or (ho arsenate. 



The arsenic for the following experiments was sublimed and 

 then heated in a current of dry hydrogen in order to remove 

 any oxide present. 



1 2 3 



Arsenic 5*000 gr. 5*000 gr. 6*000 gr. 



Sodium peroxide 23 " 19 " ' 22 " 



Water equivalent of system 4,028 " 3,945 " 3,994 " 



Temperature interval 2-667° 2*865° 3-247° 



*De Forcrand, C. E., cxxvii, 514. 



f Ann. Ch. Phvs. (5), ix, 28. 



-J-Loc. cit. §C. E., civ, 1704. 



