MAKK. — SALINITY OF SEA-WATER IN THE BERMUDAS. 073 



run in from the burette, at first nipidly, but at the end drop l)y drop, 

 until a faint reddish tinfj:e in tlie precipitate was jiermanent for thirty 

 seconds. This was taken as the end point. The cHfFercnce between 

 the vohnne of silver nitrate used, as expressed in burette divisions, 

 and the figure accompanying the standard sample was the value " a " 

 of the Knudsen tables. Obviously this method of standardization 

 shows only the strength of the solution as compared with the standard 

 upon which the Knudsen tables are based; but since the analyses 

 also are expressed in terms of this standard, no further knowledge of 

 the concentration is required. 



A secondary standard sea-water was prepared by diluting ordinary 

 sea-water till approximately the same volume of silver nitrate was 

 required to react with it as was required to react with the original 

 standartl. The exact ratio of these standards was determined with 

 great care, since the secondary standard was the one constantly used 

 during the investigation. At the end of the work, however, the silver 

 nitrate was again compared with the original standard and was found 

 to be unchanged. 



In making a series of analyses, the silver nitrate solution was each 

 day titrated against the standard water, as just described. The 

 various samples of water were then titrated in an exactly similar way, 

 and finally the solution was again compared with the standard. The 

 temperature of the room was noted during the progress of the work, 

 but in no case did it vary enough to require any correction of the 

 results. All determinations were made in duplicate. 



Accuracy. 



Since the method of analysis consists of comparing the amount of 

 silver nitrate solution necessary to react with a definite amount of 

 sea-water with that necessary to react with the same amount of sea- 

 water of known composition, no standardization of the pipette used 

 for measuring the water was necessary. The amount delivered by 

 the pipette was constant, as the time allowed for drainage was always 

 the same. 



The determination of the capacity of the burette in absolute units 

 was not required. Only the relation of the divisions to each other had 

 to be known, and these were found to be equal within the limit of 

 accuracy to which the volume could be read. These readings could 

 be relied upon to one one-hundredth of a unit. As the total volume 

 of solution used in a determination was about twentv units, the 



