OF ARTS AND SCIENCES. 97 



filtered, tlie precipitate washed with hot water, dissolved in dilute 

 sulphuric acid, and the metallic copper precipitated by a battery. 



The filtrate containing the arsenic is made acid with acetic acid, and 

 titrated wilh uranium acetate solution. 



This method was carefully tested against others and itself, and 

 proved to give the most satisfactory results. 



The acetic anhydride was determined by ignition with lead chromate 

 as in an oi-ganic analysis, collecting the carbonic acid and water, and 

 weighing the same ; the excess in weight of water above that formed 

 from the combustion of the acetic acid, gave the total water. The 

 hydroscopic water was determined by drying the salt for three or four 

 hours in an air-bath at 100° — 105° C. until a constant weight was 

 obtained, of course deducting the hydroscopic from the total water, 

 gives that which is combined. 



I owe my sincere thanks to Professor S. P. Sharpies, for his kind- 

 ness in allowing me the use of his very convenient laboratory, his 

 library, and for some suggestions as the investigation progressed. 



Boston, October 24, 187G. 



VOL. XII. (n. s. it.) 



