SPECIFIC GRAVITY AND DISPLACEMENT OF SOME SALINE SOLUTIONS. 3 



PAR. PAGE 



19. Influence of the Meniscus. The weight which causes the immersion of the hydrometer is 46 



its own weight plus that of the liquid meniscus which it carries on the stem above the 

 line of flotation. This holds good when the hydrometer is floating in the solution and 

 in distilled water alike. Each meniscus exerts the pressure of its own weight and con- 

 tributes to the displacing weight of the instrument when it floats in the distilled water 

 and the solution respectively. Data regarding the surface-tension of distilled water and 

 of saline solutions have been taken from Tables 124 to 129 of the Smithsonian Collec- 

 tion of Physical Tables, 5th edition, 1910. In a table, in this paragraph, the e0"ect of 

 introducing the weight of the meniscus in the hydrometric determination of the specific 

 gravity of some solutions has been calculated, with the result that, for a solution of NaCl 

 having a specific gravity of 1 'OSS when the weights of both meniscuses are disregarded, 

 the apparent specific gravity is increased by I '3 in the fifth place of decimals when 

 efl'ect is given to the weight of both meniscuses. .As the density of average oceanic 

 water is not greater than 1'027, the influence of the meniscus on its density would be 

 represented, at the most, by 1 in the fifth place. Therefore my practice, adopted at 

 the beginning, of disregarding the influence of meniscus on the density of sea-water, as 

 determined by my hydrometric method, is justified, 



20. Serial Determination of the Specific Gravity of a Saline Solution. The table gives the 48 



specific gravity of 1/32 RbCl in 1000 grams of water at 19 '5° C. In it the specific gravity 

 is deduced from each individual observation of four series of nine observations each, 

 making in all thirty-six independent determinations, and they agree well with each other. 

 The solutions of twenty-seven salts form the subject of the tables in Section V. They 

 are KCl, RbCl, CsCl, KBr, RbBr, CsBr, KI, Rbl, Csl, which form the ennead* having 

 the general formula MR; KCIO3, RbClOg, CsClOg, KBrOj, RbBrOg, CsBrOg, KIO3, 

 RblOg, CsIOg, which form the ennead having the general formula MRO3 ; and NaCl, 

 KNO3, RbNOg, CsNOg, LiN03, NaNOj, Sr(N03)2, Ba(N03)2 and Pb(N03)2. The 

 concentrations of these solutions vary from 1/2 to 1/1024 gram-molecule of salt per 

 1000 grams of water. In the cases of strong solutions the concentrations were from 

 1 gram-molecule per 1000 grams of water upwards. 



21. Statistics relating to the Range of Variation of Temperature during a Series of Observations. 51 



The table gives statistics of the variations of the temperature of the liquid while a total 

 of 1316 series, of nine observations each, was made with hydrometers Nos. 17 and 21, 

 namely, 837 with No. 17 and 479 with No. 21. There was no sensible variation of 

 temperature in 68 per cent, of those made with No. 17, and in 55 '2 per cent, of those 

 made with No. 21. Considering the series made with both hydrometers for which the 

 variation of temperature was not greater than 0"05° C, the percentages are almost 

 identical, namely, 89-5 for No. 17 and 89"2 for No. 21. The maximum departure of 

 the mean temperature from the standard (T), during any single series of observations, 

 was 0'12° C. ; the mean departure was0'0075° C. The maximum range of temperature 

 while a series of nine observations was being made was 0"30° C. ; the mean range cf 

 temperature for the 1316 series, of nine observations each, was 0'018° C. 



SECTION IV. 



The Control op the Temperature of the Laboratory. 



22-25. The temperature chosen is dictated by the facility of its maintenance. Four such tempera- 52 



tures are used, namely, 15°, 19*5°, 23° and 26° C. The great majority of observations 

 has been made at 19'5° C, which is a suitable temperature for an inhabited room. The 



* From the Greek iw^as, which signifies a body of nine. 



