OF ARTS AND SCIENCES. 245 



Materials used in the Analysis. 



Capric Sulphate. — The substance used in the first series of experi- 

 ments was partly prepared from very pure copper remaining from the 

 ciipric bromide research, and partly from other sources. It was per- 

 fectly neutral and reasonably pure. For the second and third .series 

 four hundred grams of the so-called '' chemically pure " cupric sulphate 

 of commerce were dissolved in a very large amount of water, and 

 the solution was twice successively treated with a very small amount 

 of potassic hydroxide in dilute solution ; the mixture being occasion- 

 ally shaken and allowed to stand each time for a week before decant- 

 ing the clear supernatant liquid. One quarter of a gram of amnionic 

 bromide was added to this liquid ; and after standing two weeks the 

 solution was carefully filtered, evaporated to very small bulk in a por- 

 celain dish, and again filtered from the deposited basic salt. The 

 finely divided crystals obtained from this solution by agitation and 

 cooling with ice were drained with a reverse filter,* redissolved in 

 hot water, and repeatedly recrystallized in platinum vessels. The 

 first three mother liquors were rejected, but the later ones were all 

 combined. After three more recrystallizations the substance con- 

 tained in these mother liquors was dissolved in cold water and allowed 

 to crystallize by slow evaporation in pure air. The prejiaration thus 

 made was used in the second series of analyses. 



The crystals obtained by eight successive crystallizations in platinum 

 vessels were dissolved in cold water, and the salt was slowly recrystal- 

 ized over sulphuric acid in a vacuum. The substance thus obtained 

 was dissolved in water which had been distilled in a platinum retort, 

 and after standing six days the perfectly clear solution was again 

 brought to crystallization in a vacuum. These crystals were dried in 

 a platinum dish over partially dehydrated cupric sulphate, and were 

 used for the third series of experiments. The neutrality of each of 

 these preparations was determined as nearly as possible by means 

 of methyl orange, after the manner described in these Proceedings, 

 Volume XXV., page 201. 



Sodic Carbonate. — As sodic carbonate formed one of the chief 

 bases for the determination of the sulphuric acid, its manufacture in 

 a pure state was a matter of great importance. From the " chemicallv 

 pure" material of commerce one may easily procure by five recrystal- 

 lizations a material which gives no coloration with ammonic sulphy- 



* These Proceedings, XII. 124. 



