16 PROCEEDINGS OF THE AMERICAN ACADEMY 



meta-tungstates with an alkaline base, appear to contain water of 

 constitution and to have an acid reaction, but it is difficult to deter- 

 mine the quantity of basic hydrogen with certainty, and the mere fact 

 that the salts have an acid reaction is not in itself conclusive evidence 

 that they are in the strict chemical sense acid. Tungstates have been 

 described by different chemists, which do not fall within either of the 

 groups given above. In all these cases, however, it will be found 

 on examination, that the analyses do not agree well with the formulas 

 assigned, and that there is reason to believe that the salts studied were 

 mixtures. I consider it at least probable that the tri-salts of Lefort 

 belong in reality to the meta-series, their molecular weights being 

 doubled. But it is of course possible that we have here cases of 

 isomerism, and I much regret that I did not succeed in obtaining 

 these salts for study and comparison. With respect to the double 

 salt which I have described above, and which has the formula 



12 W0 3 . 5 Na a O -f 10 W0 8 . 4 Na 2 + 51 aq, 



I may remark that it is possible that the compound is really 



22W0 3 . 9Na 2 + 51aq, 



and that it is not a double salt, but one term in a series which we 

 obtain by again doubling the formulas of the meta-tungstates as I 

 have given them above. The question is one which I must leave un- 

 decided for the present at least. 



The analogy between the compounds of tungsten and molybdenum 

 is in general so great, that we ought to expect to find alkaline molyb- 

 dates corresponding to the three series of tungstates. We owe to 

 Ullik the most complete examination of the molybdates which has been 

 published. A careful study of his results will show that, while we 

 have a number of molybdates to which there are apparently no cor- 

 responding tungstates, we have at least reason to believe in the exist- 

 ence of the three series of normal, meta, and pyro salts. Thus the 

 following salts may be assumed as typical : — 



Normal Series. 

 M0O3 . Na 2 + 2 aq 

 2 M0O3 . Na 2 and with 1 . H 2 



Meta Series. 

 4Mo0 3 . Na 2 + 6aq or Mo 4 0„(NaO) 2 -f- 6aq 



6 Mo0 8 . 2 Na 2 -f 14 aq " Mo G 16 (NaO) 4 + 14 aq 



8 M0O3 . Na 2 . 2 H 2 + 2 aq " Mo 8 21 (NaO) 2 (HO) 4 -f 2 aq 



