16 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



Maximum Basic Condition of Hot Chromic 

 Sulphate Solution. 



posited chromic hydroxide on boiling; and the other is the fact that this 

 boiled solution was found to be strongly acid to methyl orano- e . 



Thus the solution boiled with chromic hydroxide must contain ionized 

 hydrogen, and hence the basic substance present must be even more basic 

 than CrOHS0 4 , the agreement with this formula being accidental. 



In accordance with this inference, it was found that dilute caustic 

 alkali could be added to the solution without producing a permanent 



precipitate. The same result — the removal of the ionized hydrogen 



may be better accomplished by shaking the solution at ordinary tempera- 

 tures with chromic hydroxide. Even the violet solution may be quickly 

 converted into the green in this way, as Siewert has shown. The 

 hydroxide was prepared by cold precipitation with a slight excess of 

 ammonia, and was washed until free from sulphuric acid. The violet 

 solution was treated with an excess of this precipitate, and the mixture 

 was shaken in a tightly stoppered bottle in an automatic shaking machine 

 for several days, portions being removed from time to time for analysis. 

 Opposite are given the results of this work. The solution was fourth- 

 molar and the temperature about 20°. 



The constant results indicate saturation. Thus a decrease in acid 

 from 1.97 to 1.59 — or perhaps better an increase in base from 2.00 to 

 2.48 — occurs on cooling in the presence of excess of hydroxide. This 

 ratio corresponds almost exactly to Cr 6 : (S0 4 ) 4 , a relation which de- 

 mands the complex formula Cr 5 (S0 4 ) 4 (OH) 7 . The possibility still 

 existed that some ionized hydrogen was present even at 20°, because so 

 much more ionized hydrogen was needed at 100° in order to preserve 

 the equilibrium. 



In order to test this point the rate of inversion of sugar at 30° by this 



