New Forms of Stereometers. 311 



This form of the apparatus is therefore fairly satisfactory. 



The adjustment of the mercury in the constricted 

 portion of the tube can easily be effected, and the capillary 

 error is removed by making all the readings on the wide 

 tube (the diameters of the various constricted portions 

 being approximately equal). 



It was found impossible to diminish the pressure to less 

 than about 100 mms., as air then passed rapidly through 

 the walls of the india-rubber tubing, although the latter 

 was specially thick, and had been soaked in paraffin (Cf. 

 Roscoe and l^uni^ Journ. Chem. Soc. 1889, p. 564). 



A few experiments were made to determine the sp. gr. of 

 water by this method, 7* 1225 grms. of water at 17° were 

 introduced into the apparatus in a small glass tube of 

 volume = 4097 grms. 



In calculating the results of these experiments it is 

 necessary to allow for the aqueous tension (Cf. Grassi. loc, 

 <:it.). 



As before let Vj, V2, Pi, Pg, be the actual vols, and 

 pressures. Then 



For Pi substitute~pi = Barometer - Aqueous tension. 



Then P2 - P^ = Bar. - Aq. ten. - diff. of level - (Bar. - Aq. 

 ten.), and the equation becomes 



The water was freed from air by the air pump. 

 T=i7° 3 = 763. 



X Observed. x Calculated, 



(i) 7-i8 



(2) 721 



(3) 7*11 



Mean 7-17 7*132 



Error =-038 = -53%. 



In Grassi's experiments with Regnault's apparatus the error 



was '44%. 



