OP ARTS AND SCIENCES. 183 



subsequent exhaustion produced no sensible effect on the result, as a 

 knowledge of the volume within five cubic centimeters was all that the 

 present problem required, and the water did not lose in weight more 

 thau two grams during the whole series of experiments. 



The balloon was now thoroughly exhausted, allowed to stand, and 

 again exhausted several times, until a vacuum gauge connected with 

 it remained constant over night, and indicated the calculated tension 

 of aqueous vapor, which showed that all the air — dissolved or other- 

 wise — had been practically removed. 



A sufficient mass of water was left in the balloon to sink it under 

 water, and thus immersed in a large vessel filled with distilled water, 

 (which had been boiled and allowed to cool,) it was now suspended 

 from the beam of the balance used throughout this investigation. No 

 air bubbles formed on the glass, and care was taken to remove all 

 entangled air from the connecting tubes. The weight soon became 

 constant, and the tare could be accurately determined within a centi- 

 gram. The connecting tubes of the balloon were next lifted above the 

 surface of the water, and, after carefully drying the inlet, the outside 

 air was admitted, and the temperature of the water in the tank and 

 the height of the barometer observed. On again immersing the bal- 

 loon there was a large loss of weight, — about 1.4 grams, — over six 

 times the weight of air admitted, — only about 0.2 gram. There had 

 evidently been a marked shrinkage under exhaustion amounting to 

 about 1.6 cubic centimeters. This decrease of weight was noted after 

 the equilibrium had become constant, usually in about five minutes. 



It is probable that the admitted air was saturated with moisture, 

 and the calculation is based upon that assumption ; but this would 

 make no practical difference in the weight so far as the problem before 

 us is concerned. Appended is an example of the method. 



Series I. Determination 2. 



Tare of globe exhausted = 198.22 grm. T° = 17°.30. 

 « filled = 196.83 " T° = 17°.30. 



Observed loss of weight == 1.39 " 



Atmospheric pressure = 75.86 c. m. 

 Tension of aqueous vapor = 1.46 " 



Difference = 74.40 " 



