18 RESEARCHES ON THE 



It is true that the analyses here agree with the formula as well as can be 

 reasonably expected. We have, however, found in other crystals from the same 

 mass 17.82, 17.86, 17.92, 18.06 per cent, cobalt, numbers which agree much better 

 with the formula of an anhydrous nitrate, having the same formula as the nitrate 

 of Roseocobalt already described, which contains 17.87 per cent. In any event, 

 the doubt appears to be simply Avith respect to the quantity of water in the salt, 

 the ratio of the equivalents of cobalt and nitrogen being as 1 to 4, or 2 to 8. We 

 shall return to this point at another time. 



OXALATE OF ROSEOCOBALT. 



The oxalate is precipitated from the chloride almost immediately by the addition 

 of a solution of oxalate of ammonia. From a solution of the nitrate it is 

 deposited much more slowly, often only after some hours, and sometimes in 

 remarkably distinct and well formed crystals. The oxalate as first thrown down 

 may be purified by solution in ammonia-water and recrystallization by spontaneous 

 evaporation. The salt then forms beautiful prismatic crystals, which are nearly 

 insoluble in water, and which have a fine cherry-red color, resembling the crystals 

 of sulphate of Roseocobalt. The crystals are dichrous, the ordinary image being 

 pale violet, while the extraordinary image is dark rose-red. The precipitated 

 oxalate has a dull brick-red color. According to Prof. Dana, the crystals of oxalate 

 of Roseocobalt belong to the right rhombic or trimetric system, the observed forms 

 being a rhombic prism of about 101° 48', with a brachydome of 108° 54'. 



The constitution of the oxalate of Roseocobalt is represented by the formula, 

 5NH 3 .Co 2 Q3,3C 2 3 +6HO 



as the following analyses show : 



0.5504 grs. gave 0.2625 grs. sulphate of cobalt = 18.15 per cent. 



0.3325 grs. gave 0.1585 grs. " " =18.14 



1.5381 grs. gave 0.6170 grs. carbonic acid = 32.82 per cent, oxalic acid. 



The formula requires 





Eqs. 



Calculated. 



Found. 



Cobalt . 



2 



11.81 



18.15 18.14 



Oxalic acid 



. 3 



32.13 



32.82 — 



COBALTIDCYANIDE OF ROSEOCOBALT. 



This beautiful salt is precipitated from a solution of the chloride or hydrous 

 nitrate of Roseocobalt, by a solution of cobaltidcyanide of potassium. It may be 

 prepared with equal facility from a solution of the chloride of Purpureocobalt, 

 which under these circumstances, as we conceive, undergoes a direct change into a 

 salt of the triacid Roseocobalt. The cobaltidcyanide is usually precipitated at 

 once in the form of cherry-red prismatic crystals, which, so far as it is possible to 

 judge from their appearance under the microscope, belong to the oblique rhombic 



