8 PROCEEDINGS OP THE AMERICAN ACADEMY 



sulphate carefully washed to avoid loss of nitrate. From the filtered 

 solution the new salt crystallizes almost completely, on cooling, in 

 beautiful orange-yellow needles, and sometimes in distinct prismatic 

 forms. It is much more soluble than the sulphate, though cold water 

 takes up but little. Boiling water and dilute acid solutions dissolve it 

 more readily. The reactions of the base may be studied most con- 

 veniently with this salt. The formula of the nitrate is 



Co,(NH3),(NO,X(N03)„ 



as the following analyses show : — 



0-2405 gr. gave 0-1333 gr. CoSO4 = 2M0 per cent cobalt. 

 0*6564 gr. gave 0-2484 gr. water = 4-21 per cent hydrogen. 

 0-6148 gr. gave 173-5 c.c. nitrogen at 4-5° C, and 762-2°"" = 34-83 

 per cent. 



662 100.00 



The nitrate explodes, though not very violently, on being heated. Its 

 solution gives with potassic ferrocyanide no precipitate at first, but 

 after some hours beautiful garnet-red acicular crystals are formed. It 

 is most easily distinguished from the nitrate of xanthocobalt by its 

 crystalline form and by the extremely characteristic precipitates which 

 its solution yields with potassic hyperiodide and with potassic chromate. 

 Ghromate. — When a solution of potassic chromate is added to one 

 of the nitrate of the octamin series, a most beautiful lemon-yellow salt 

 is formed, which separates almost immediately in very brilliant scales 

 which appear to belong to the quadratic system, and to be isomorjjhous 

 with the sulphate. The salt is but slightly soluble in water. Its 

 marked crystalline form renders it valuable in di-tinguishing the salts 

 of this series from those of xanthocobalt. In this salt, 



0-4660 gr. gave 0-2128 gr. BaCr04= 20-95 per cent CrO^. 

 0-4659 gr. gave 119-5 c.c. nitrogen at 9-75° C. and 753-5°"" = 30-42 

 per cent. 



The formula, Co,XNHo),(NO,)4CrO^, requires 20-97 per cent CrO^ 

 and 30-42 per cent of nitrogen. 



Dichromate. — This salt is easily formed by adding a solution of 

 potassic dichromate to one of the octamin nitrate. It separates after 

 a few minutes in beautiful orange-yellow needles, which may be redis- 



