Van Name and Bosworth — Silver Sulphate, etc. 293 



Art. XXIII. — On Mixed Crystals of Silver Sulphate and' 

 Dichromate ; by R. (x. Van Name and Rowland S. 

 Bosworth. 



[Contributions from the Kent Chemical Laboratory of Yale Univ. — ccviii.] 



1st 1891 Retgers* described an attempt to form mixed crys- 

 tals of silver chromate and sulphate by allowing an ammonia- 

 cal solution of the two salts to evaporate. The two silver salts 

 were found to crystallize separately and no mixed crystals 

 were obtained. The failure of this experiment makes it seem 

 doubtful whether the sulphate and normal chromate of silver 

 possess, to any appreciable extent, the property of forming 

 mixed crystals together, especially since Retgers was unable 

 to obtain mixed crystals of the corresponding sodium salts. 



We have found, however, that if the solution be sufficiently 

 acid, and the ratio of chromate to sulphate w T ithin certain nar- 

 row limits, well developed crystals are formed, of colors rang- 

 ing from pale yellow through shades of orange and vermillion 

 to a deep scarlet, according to the value of the ratio just 

 mentioned. Analysis of these crystals shows that they con- 

 sist of silver dichromate and normal silver sulphate in varying 

 proportions. As these mixed crystals have not, so far as we 

 know, been described heretofore, it has .seemed desirable to 

 carry out the following brief investigation of their properties. 



A series of crystallizations was made at 25° starting with 

 solutions of the same total acidity, about one fourth normal, 

 but containing different proportions of the two acids. The 

 change in concentration caused by the crystallization was kept 

 as low as practicable by using in each experiment a large 

 volume of solution, two liters, and so choosing the conditions 

 that equilibrium w r as reached when only a small weight of 

 crystals, usually less than three grams, had been formed. As 

 will appear later, mixed crystals were only obtained when the 

 molecular ratio of S0 4 to Cr 2 7 in the solution was above 99 

 to 1. An increase in the proportion of Cr 2 7 gave only pure 

 crystals of silver dichromate, so that the investigation of solu- 

 tions containing high proportions of dichromate was unneces- 

 sary. It was therefore possible to obtain a sufficient range of 

 concentration of dichromate for all needed experiments by 

 merely dissolving various amounts of silver chromate in the 

 same volume of the standard sulphuric acid solution, previously 

 warmed. When a higher concentration of silver was required 

 silver sulphate was also added. 



The different sulphuric acid solutions were adjusted to 



*Zeitschr. phys. Chem., viii, 52, 1891. 



Am. Jour. Sci.— Fourth Series, Vol. XXIX, No. 172.— April. 1910. 

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