81 



On Assaying Silver. 



[April 



Supposons que le poids de la burette pleine de 



dissolution de sel titree de grammes 307 



Et que son poids apres 1'essai, soit de 217 



On aurait employe en dissolution de sel 90 



Ce qui representerait exactement le titre de 900 milliemes. 

 En supposant que la burette pleine de 



dissolution saline titree, pesat, avantl'essai 307.56 

 Et apres l'essai 217.00 



La dissolution employee peserait 90.56 



Ce qui donnerait le titre de 905 milliemes 6. 



14. The method of assay thus developed is founded on 

 Strict chemical principles, and depends on the play of chemi- 

 cal affinities. The solution of silver in nitric acid is a test 

 for muriatic acid ; and common salt, which contains muriatic 

 acid is a test for nitrate of silver. The two mutually de- 

 compose each other. The silver combines with the muriatic 

 acid, and forms an insoluble muriate of silver, and the soda of the 

 common salt combines with the nitric acid and forms a solu- 

 ble nitrate of soda ; and when the relative quantities of each, 

 required to produce complete mutual decomposition are 

 known, the principle of the process is obtained. 



15. These relative quantities are found by means of a ta- 

 ble of chemical equivalents, thus ; the equivalent number of 

 silver is 108 0 and of common salt (muriate of soda, or chlo- 

 ride of sodium) is 58*75 :* which means that a solution of 

 58*75 grains of pure dry common salt, will decompose exact- 

 ly 108 grains of silver dissolved in acid. From these num- 

 bers therefore may be calculated the proportion of salt and 

 of silver required for an assay of any given quantity. 



16. Suppose the assay pound should be equal to 10 troy 

 grains ; then 544 grains of pure dry common salt would be 

 required to precipitate ten grains of pure silver : for as 

 108 : 58-75 ;; 10 = 5*44, and if distilled water were added 



* Table by Dr. Turner, 1833. 



