34 PROCEEDINGS OF THE AMERICAN ACADEMY 



The formula requires 94*39 (y^ of the mixed sulphates 2SO^Co-|- 

 SSO^Tl^, and 1*8G% water. The salt is partially decomposed above 

 140'^ C. 



The thallium salt is very slightly soluble even in boiling water. 

 Its formation is expressed by the equation, — 



Co,(jSrO.)j,Lc+6TlNO, = Co,(NO,)i.Tl,+Lc(N03)e. 



It may also be prepared directly by adding a solution of a salt of cobaltic 

 nitrate or sulphate to a hot solution of thallous nitrate containing a 

 slight excess of free acid, and tlien adding a solution of sodic nitrite? 

 The salt prepared in this manner, however, is apt to cojitain a little of 

 the corresponding sodium salt. The thallium salt is a valuable re- 

 agent in investigations on the cobalt compounds which contain nitroxyl. 

 NOg. since, taken in connection with the characteristic silver salt of 

 Erdmann's series, it enables us to recognize and distinguish compounds 

 which contain Co2(N02)j., from those which contain Co2(NH„)^(N02)«, 

 which is otherwise by no means easy. 



The relationship of the luteocobalt salf above described to the other 

 metameric salts of the series may be expressed as follows : — 



lCo,(NH,),,nCo,(NO,),J = 2.Co,(NH3),(NO,)„ 



the salt having the same atomic weight as the octamiu salt already 

 described represented by the formula, — 



Ammonia-cohalt-nitrite of Luteocobalt, — A solution of nitrate of 

 luteocobalt gives with one of Erdmann's salt of potassium, Co2(NH.,)^ 

 (NO.,)^K.„ a fine granular orange-yellow precipitate, which is slightly 

 soluble in cold water, but dissolves in much boiling water, and crystal- 

 lizes from the solution without cliange. Its much greater solubility 

 distinguishes it from the metameric salts containing Co2(N02)io- The 

 constitution of this salt is expressed by the formula, 



^Co,(NII3),JlCo,(XH,),(^'0,);i3 or Co,(NH3),,(N0,),+ 

 (Co,(XIL),(NO,),)3, 



as the following analyses show : — 



0-3311 gr. gave 0-2077 gr. SO.Co = 23-88 9/^ cobalt. 

 0-5073 gr. gave 141-5 c.c. nitrogen at 9^C. and 7G0""" = 33-86% 

 nitrogen. 



The formula requires 23-79 <7^ cobalt, and 33-87% nitrogen. 



A solution of this salt gives with argentic nitrate the characteristic 



