OF ARTS AND SCIENCES. 7 



1-2456 gr. gave 0-5387 gr. Co^P.O.j by ignition = 43-24% and 



56-70% water, ammonia, and oxygen. 

 1 4484 gr. gave 0-9415 gr. water (burnt with CuO) = 7.22% hy'gen. 

 1-0964 gr. gave 0-3911 gr. water = 35-67% water of crystallization. 



The formula Co2(NH3)j„P,Oi3-}-2lOH2 requires 43-48 %Co,PPj2, 

 and 56-52% 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,(NH3),„Cl,+2P,0,]SX+Oa, = Co,(NH3),,P,0,34-6NaCl+ 



20NaH. 



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,(NH3)jo.P,Oi3 = 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 pyrophosphate of purpureocobalt furnishes, if the formula given 

 be adopted, an instance of a true dipyrophosphate bearing the same 

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

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

 words, two molecules of P^O-H^, or P203.(OH)^ are fused together, so 

 as to form a single molecule of P^OjjH,,, or P^O.(OII)e, an atom of 

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



2.P,03.(OH), = PA-(OH),+OH,. 



The structure of dipyrophosphoric acid may be briefly represented by 

 the expression : — 



3(0H) E (PA)— 0-(P203) E (0H)3. 



The corresponding salt of luteocobalt presents a similar instance. 

 According to Braun, the whole of the water of crystallization is given 

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

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

 atoms requires 36.07%. 



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

 manu's series, Co2(NH3)^(NO^)gK2, 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 



