OF ARTS AND SCIENCES. 7 



1-2456 gr. gave 0-5387 gr. Coj',0|^, by ignition = IS^l^ and 



5G'7G(fo water, ammonia, and oxygen. 

 1 4484 gr. gave 0-9415 gr. water (burnt with CuO) = 7.2-2% liy'gen. 

 1'09G4 gr. gave 0-3'.)ll gr. water = 35-67% water of crystallization. 



The formuhi Co,(NII,),oP,0,,+-2lOII, reiiuires 43-48 %Co,P,0,2, 

 and 56-529^ water, ammonia, and oxygen ; also 7*21% hydrogen, and 

 37'87<^ water of crystallization. These analyses fully confirm 

 Braun's results. The formation of the salt from sodic pyrophosphate 

 and chloride of purpureocobalt may be represented by the equation: — 



Co,(NII,),,Cl,+2PA-Na,+0ir, = Co,(NIl3),„PA3+6NaCl+ 



20NaII. 



The mother liquor from which the pyrophosphate has crystallized has 

 a strong alkaline reaction. The decomposition of the salt by heat 

 may be expressed by the equation : — 



Co,(NIl3),„.P,0,3 = Co,P,O,,+O-[-10NH3, 



though it is of course most probable that a part of the ammonia is 

 oxidized to water and nitrogen. 



The pyi'ophosphate of purpureocobalt furnishes, if the formula given 

 be adopted, an instance of a true di-pyrophosphate bearing the same 

 relation to the ordinary salts of the acid which the disulphates, dichro- 

 mates, &c., bear to the normal sulphates and chromates. In other 

 words, two molecules of PgO-H^, or P20g.(01I)4 are fused together, so 

 as to form a single molecule of P^Oj.^H^, or P^O.(OH)g, an atom of 

 water being given off. Thus'we have in symbols : — 



2.PA.(0H), = PA-(OH),+OH,. 



The structure of dipyrophosphoric acid m-ay be briefly represented by 

 the expression : — 



3(0H) ~ (PA)_0-(P,0,) Z (Oil),. 



The corresponding salt of luteocobalt presents a similar instance. 

 According to Braun, the whole of the water of cryst;dlization is given 

 off at 100°C. ; but I found that one atom was retained at that tempera- 

 ture, the loss in my analysis being 35.67°, while the formula for 20 

 atoms requires 36.07%. 



Ammonia-cobalt-nitrite. — A solution of the potassium salt of Erd- 

 mann's series, Co2(NH3)^(NO^,)gK^, gives with nitrate of purpureo- 

 cobalt a beautiful very dark orange-red precipitate in crystals, which 

 are sometimes acicular, and sometimes granular. The crystals are not 



