1877.] On Double Salts of Nitrate of Silver. 357 



sand, and peas selected of good round form, and other small round seeds, 

 such as clover- seed and poppy-seed. Granules such as these showed 

 very clearly numerous phenomena, not only of the flow of the water, but 

 also of the transmission of material-like detritus forward along the 

 bottom in straight parts, and very obliquely across the bottom in the 

 bend ; and gave imitations on a small scale, easy for observation, of the 

 processes of accumulation of detritus along the inner banks of the bends 

 of rivers, and presented also interesting suggestions and considerations 

 as to some of the details or secondary actions involved in the processes *. 



VII. " An Attempt to form Double Salts of Nitrate of Silver 

 and other Nitrates/' By W. J. Russell, Ph.D., F.R.S., 

 and Nevil Story Maskelyne, F.R.S. Received June 21, 

 1877. 



(Abstract.) 



When a solution containing silver and potassium nitrates, in equiva- 

 lent proportions, is evaporated, the potassium nitrate separates out, un- 

 combined with silver nitrate. If, however, the ratio of silver nitrate to 

 potassium nitrate be increased beyond a certain limit (which has been 

 determined), then a true double salt having the composition AgN0 3 KN0 3 

 crystallizes out. The same salt can also be formed from a solution that 

 would not yield it under ordinary circumstances, by either adding nitric 

 acid or by increasing the temperature of the solution, both these altera- 

 tions tending in the same direction, viz. to decrease the amount of silver 

 nitrate as compared to that of potassium nitrate which can exist in solu- 

 tion. 



Further it is shown, with regard to these two salts, that if an intimate 

 mixture of them be treated with an amount of water insufficient to dis- 

 solve the whole of either constituent, still the composition of the solu- 

 tion found will vary with the composition of the mixture used. This 

 arises from the two salts uniting in solution to form the double salt, and 

 ultimately the amount of double salt that can remain in solution depend- 

 ing on the excess of silver nitrate present, which, from its greater solu- 

 bility, can displace the double salt from solution. The residue in this 

 case, from its crystalline form, can be identified as double salts. 



With sodium nitrate a corresponding double salt does not form. In 

 this case, on evaporating the solution it is the silver nitrate, not the 



* The experiments here described were shown in the Mathematical and Physical 

 Section of the British Association at the meeting held at Glasgow, in September 1876, 

 and further in the temporary collection prepared in the Helvingrove Museum at 

 Glasgow, for that meeting of the Association. As they were arranged expressly for 

 testing and illustrating the theoretical views contained in a paper previously submitted 

 to the Eoyal Society, the present brief account of them is offered here to the Society 

 as a sequel to that previous paper. 



