OP ARTS AND SCIENCES. 133 



probable that the salt is a compound of two acid salts of a 7-atom 

 series, and that its formula is 



7 W0 3 . P 2 5 . 3 Na 2 . 3 H 2 -f 7 W0 3 . P 2 5 . 2 Na 2 . 4 H 2 + 35 aq. 



Among the corresponding phospho-molybdates there is at least one 

 series in which the number of atoms of the teroxide is odd. Po- 

 tassium and ammonium salts in this series have respectively the 

 formulas 



5 M0O3 . P 2 3 . 3 K 2 . 3 H 2 + 4 aq, 

 5 M0O3 . P 2 5 . 3 (NH 4 ) 2 . 3 H 2 + 4 aq, 



if, provisionally, we consider the acid as 12-basic. "With respect to 

 the formula given above, and which is that of an acid double salt, 

 I may remark that I shall describe farther on a salt of the 5-atom 

 molybdenum series with the formula 



5 M0O3 . P 2 5 . 3 (NH 4 ) 2 . 3 H 2 + 5 MoO s . P 2 5 . 2 (NH 4 ) 2 . 4 H 2 0, 



and that Rammelsberg has already described the corresponding potas- 

 sium compound. From the general analogy between tungsten and 

 molybdenum, the existence of phospho-tungstates with an uneven 

 number of atoms of tungstic oxide may be fairly inferred from that 

 of phospho-molybdates of the type of the 5-atom compounds above 

 mentioned. I must leave the question undecided, for the present at 

 least, as I have not succeeded in obtaining corresponding salts of 

 potassium, ammonium, strontium, or calcium. 



The salt crystallizes in long, flat prismatic forms, and appears to be 

 perfectly homogeneous, so that I believe it should be regarded as a 

 definite compound, and not as a mixture. It is very soluble in water, 

 and crystallizes only from sirupy solutions. It has a strongly marked 

 sweet taste, which is at the same time astringent and very slightly 

 bitter. The solution of the sodium salt gives with potassic bromide 

 a beautiful crystalline precipitate, already described, and having the 

 formula 



16 W0 8 . P 2 5 . 4 K 2 . 2 H 2 + 19 aq, 



and with ammonic chloride, the ammonium salt 



16 W0 3 . P 2 5 . 6 (NH 4 ) 2 + 10 aq, 



also noticed above. 



I endeavored to obtain the normal 6-atom sodium salt 6 W0 8 . 

 P 2 5 . 6 Na 2 by boiling six atoms of neutral sodic tungstate with 



