OF ARTS AND SCIENCES. 21 



but I shall content myself with citing. a single case, which has not 

 been discussed, and which, strangely enough, has attracted but little 

 attention. I refer to the remarkable series of compounds of molyb- 

 denum studied by Blomstrand* and by Atterberg.f Representative 

 terms in this series are expressed by the formulas 



Mo 8 Cl 4 • Cl 2 Mo 3 Cl 4 . (OH) 2 Mo s Cl 4 . Br 2 



Mo,Br 4 . Br 2 Mo 3 Br 4 . (OH) 2 Mo 8 Br 4 . S0 4 



omitting water of crystallization for greater brevity. The action of 

 alkalies upon the bromide Mo 3 Br 4 . Br 2 produces first Mo a Br 4 . (OH) 2 , 

 and afterward Mo 3 (OH) 4 (OH) 2 , or Mo 3 (OH) 6 , the hydrate of the pro- 

 toxide of molybdenum, usually written MoO . OH 2 , or Mo(OH) 2 . 

 There is therefore good reason to believe that the lowest expression 

 for this hydrate is Mo 3 (OH) 6 , the structural formula of the cor- 

 responding bromide being, perhaps, 



Mo = Br 2 

 Mo = Br 2 

 Mo = Br 2 . 



In this formula the end atoms of molybdenum are tetratomic, and the 

 middle atom hexatomic, which will perhaps explain the fact that 

 there are but two movable atoms of bromine in a whole series of salts. 

 If molybdic protoxide is Mo 3 3 , it is probable that the teroxide is not 

 MoO. { , but rather some higher multiple of this expression, and we may 

 extend the inference to WO., also. 



With these preliminaries, I pass to the special subject of my 

 work. 



* Journal t'ur prakt. Chemie, lxxxii. 436. 



t Nagra bidrag till Kannedomen om Molybden, Stockholm, 1872, p. 16. 



( To he continued.) 



