GIBBS. — COMPLEX INORGANIC ACIDS. 269 



we assume that this oxide is present in the auramin pyrophosphate 

 which I have described, we may write the formula 



8 AuA . 6 P^OTAu'^Na . 6 {(N^H^Au^OO} (NH4)20 . 2H2O + 24 aq., 



which is reducible to the type 



8 R2O3 . 7 RO + 6 P207R'4 + 26 aq. 



As regards the deduction of the formula from the analyses, it may 

 be worth while to give also the equations 



G P2O5 + 3 Au.Og + 3 NaoO = 6 PaO^Au'^N ; 

 3 AU2O3 + 12 NH3 = 6 {(N^HjAu^OO} + 3 HA 



In the determination of the ammonia by boiling with KHO or 

 NaHO, we have 



6 NJIsAu'" + 3 H2O = 12 NH3 + 3 AU2O3. 



Auro-pijrophospho-MoIyhdates. 



When a solution of chloro-aurate of sodium, AuCLNa, is mixed 

 with one of pyrophospho-molybdate of sodium, a dull orange-colored 

 fine-grained crystalline precipitate is thrown down, which is almost 

 certainly an auro-pyrophospho-molybdate of sodium. When a solution 

 of auro-pyrophos]ihate of sodium, PoOvAuNa, is boiled for some time 

 with 14:6 molybdate of ammonium, a pale buff-colored crystalline 

 precipitate is formed, which is sligiitly soluble in boiling water, giving 

 however only a turbid liquid. After washing with cold water this 

 precipitate was dried in pleno over sulphuric acid. Of this salt: 



0.5581 gram lost by ignition with W04Na2 0.0841 gram = 15.07% 

 H.,0 + Nil, + O. 

 f 0.8123 gram gave 0.3489 gram gold = 42.94% = 48.18% AU2O3. 

 1 0.8123 gram gave 0.0837 gram P.O^Mgo = 6.59% P2O5. 



0.6133 gram gave 0.2615 gram gold = 42.13% = 47.85%. 



0.2746 gram gave 0.01558 gram NH3 = 5.65% NH3. 



0.4774 gram lost by ignition with WO^Nag 0.0744 gram = 15.58%. 



In this last analysis the salt had probably absorbed a little water. 

 The same is true for the next; 



0.6133 gram gave 0.0624 gram PaO^Mga = 6.51%. 

 If we calculate the analyses for an anhydrous salt, we find: 



