ThiocyanafocoJxiJtojis Acid 157 



large excess. Most of the K.SOj precipitates and can be filtered off. The 

 deep-blue alcoholic solution was evaporated on a water bath nearly to 

 dryness and alcohol added. More K.Sd could now be removed and three 

 or four repetitions of this process proved sufficient for the complete re- 

 moval of sulfate. The sulfate-free alcoholic solution was evaporated 

 with occasional additions of a little water until the alcohol was removed 

 and the concentrated aqueous solution allowed to crystallize at room 

 temperature. Crystals of the potassium salt several centimeters long 

 were thus obtained. Analysis of the crystals, removed from the mother 

 liquor and dried by pressing between filter paper, gave: SCN=.52.6.5% ; 

 Co=13..53'7c. K,Co(SCN)4.4H.O requires SCN=52.61; Co-=13.35. 



After exposure to air: 24 hours, SCN=54.997c ; Co=13.69%; 96 

 hours, SCN=55.09^/f , Co=14.29% ; 144 hours, SCN=-55.157c, Co=14.04%. 

 K.Co(SCN)4.3H.O requires SCN=54.85%, Co=13.92?r. Evidently the 

 trihydrate, and not the tetrahydrate, is the form stable in air at room 

 temperature. 



The ammonium complex salt was prepared in anhydrous fonn by 

 precipitation from its acetone solution by chloroform and dried in air. 

 Found, SCN=69.177f ; (NH4)2Co(SCN)4 requires' SCN=70.97%. The 

 salt was dissolved in water and the solution, when evaporated at low 

 temperature, yielded fine blue needles often several centimeters long. 

 This material, when removed from the mother liquor and dried by 

 pressing between filter paper, gave SCN=60.757c ; after exposure to air 

 48 hours, 60.44 9( ; after 72 hours, 61.03%; after 96 hours, 61.22%. The 

 tetrahydrate requires SCN=58.169c ; the trihydrate requires SCN= 

 60.91%. The trihydrate appears to be the form of the ammonium salt 

 also which is stable in air at room temperature. 



By the same method of removal of alkali sulfate by alcohol it was 

 found possible to obtain the purple Co(SCN)2.3H,.0 by adding to con- 

 centrated aqueous solutions of CoSOi the calculated amount of NaSCN. 

 The product was well crystallized and contained only a spectroscopic 

 trace of sodium. In appearance and reactions it corresponded exactly 

 with the description of Rosenheim and Cohn but analysis gave Co= 

 22.17%, SCN=54.19%. Co(SCN).3H.O requires Co=25.77%, SCN= 

 50.66%. This salt is unstable in air and passes into a yellow-brown 

 substance, readily soluble in alcohol to a deep-blue solution and in ap- 

 pearance corresponding to the hemihydrate, Co(SCN)2.V2H,0, described 

 by Rosenheim and Cohn. 



Summary. 



1. The partition of cobalt between water and aqueous-alcoholic- 

 ether in presence of thiocyanic acid was studied. The ether layer was 

 found to contain equivalent proportions of cobalt and thiocyanate, in 

 addition to large amounts of thiocyanic acid, but to dissolve practically 

 no cobalt thiocyanate or alkali thiocyanate. 



2. The data obtained in this study do not permit definite conclusion 

 as to the formula, or formulas, of the extremely ether-soluble blue 

 cobalt compounds, although the evidence makes it highly probable that 

 one or more complex acids having cobalt in the anion are present. 



