Mixter — Formation of the Oxides of Molybdenum, etc. 493 



for the difference of 6*4 C between Thomsen's result and the 

 writer's is not apparent. He stated that the hydrolysis of SeCl 4 

 is complete and is probably right in this view since selenium 

 dioxide dissolves in dilute hydrochloric acid without appre- 

 ciable heat effect. 



E. Metzner* found the heat of H 2 Se0 4 ,Aq to be the 

 same as that H 2 S0 4 ,Aq. On the assumption that the heat 

 effect of Se0 3 ,H 3 is the same as S0 3 ,H 2 0, he calculated that 

 Se + 30 = 42'1 C , using Se,30, Aq = 76'660 c (T). That is, Se0 2 - 

 + O = — 14*4 C . This explains, according to Metzner, why 

 Se0 3 can not be isolated. The view that Se0 2 + O is an 

 endothermic reaction accords with the results of the experi- 

 ments with sodium peroxide. The observed heat effect of 

 Na 2 2 ,Se0 2 is 90'6 C ; adding 14'7 C , the heat absorbed by the 

 oxidation of Se0 2 gives 105'3 C for the heat effect of Na 2 0,- 

 Se0 3 . If we consider Se,20=63*5 and subtract 14* 7 C we have 

 for Se,30=48-8 C and 



Na o + Se + 30 = 154-l c 



Se "+ 30 = . _ 48'8 C 



Xa 2 + Se0 3 = _. 105-3 C 



This result is identical with that found from the reaction 

 between Xa 2 2 and Se0 2 , but substituting another number for 

 14/7 in the calculation will give equal numbers. The heat of 

 formation of Na 2 Se0 4 in solution calculated from Thomsen's 

 data is 262'3 C ; subtracting 99'8 for the heat effect of 2Na,0 

 gives 162'5 C for Na 2 0,Se,30. The heat of solution of 

 Na 2 Se0 4 has not been determined but it is negligible, as a 

 rough test with 15 grams of Na 2 Se0 4 in 200 cc of water gave 

 a rise of approximately 0*l c . The writer is unable to explain 

 why 154'1 C obtained by burning selenium with sodium peroxide 

 is so much lower than the number derived from Thomsen's 

 experiments. 



It should be stated that attempts were made to determine 

 the heat of formation of selenium dioxide by burning in a 

 bomb a mixture of selenium and charcoal. In one instance 

 the bomb was filled with a crystalline mass of selenium 

 dioxide, but the combustion was incomplete. In other experi- 

 ments the mixture burned only on the surface. 



Tellurium. 



The tellurium used in the work was purified by dissolving 



the crude metal in acid and making a fractional precipitation 



with sulphur dioxide or by recrystallizing the nitrate. The 



precipitated tellurium was fused in hydrogen. Tellurium and 



* Ann. Ch. Phys. (7), xv, 225. 



