OF ARTS AND SCIENCES. 21 



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

 been discussed, and which, strangely enough, lias 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 s Cl< . (Oil), Mo.Cl, . Br 2 



Mo,r>i- 4 . Br a Mo 8 Br 4 . (OII) 2 Mo 8 Br< . S0 4 



omitting water of crystallization for greater brevity. The action of 

 alkalies upon the bromide Mo.Br, . Br a produces first Mn lir ( . (OII)_„ 

 and afterward Mo 8 (OH) 4 (OH) a , or Mo,(OII\ ; , the hydrate of the pro- 

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

 There is therefore good reason to believe that the lowest expression 

 for this hydrate is Mo, (Oil),., the structural formula of the cor- 

 responding bromide being, perhaps, 



Mo = Br 2 



:i 

 Mo = Br 2 



II 

 Mo = Br 2 . 



In this formula the end atoms of molybdenum are tetratomie. 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 ;j O ; . it is probable that tlve teroxide is not 

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

 extend the inference to W0 3 also. 



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

 work. 



* Journal fur prakt. Chemie, Ixxxii. 436. 



t N&gra bidrag till Kannedomen om Molybden, Stockholm, 1S72, p. 16. 



( To be continued.) 



