Section 76. Apparatus and Procedure. 195 



To prevent contamination of the solutions by carbon dioxide or other 

 gases in the air, they were kept in closed bottles, and blown out through 

 an exit tube by means of compressed air which was purified by passing 

 through a train of bulbs containing sulphuric acid and potassium hydrox- 

 ide solutions. In filling the bomb, a procedure similar to that of Noyes 

 and Kato was followed ; and the results show that appreciable con- 

 tamination by carbon dioxide was excluded. After the bomb was closed, 

 the air was exhausted by means of a water-jet pump or a mechani- 

 cal vacuum pump (see also section 79). The residual pressure was read 

 on a mercury vacuum-gage. 



The bomb in its carriage was then placed in the 18 bath and rotated 

 until the resistance became constant, after which nine readings were taken, 

 three on each of three known resistances, such as 101, 110, and 1,000 

 ohms. The 218 bath had meanwhile been heated and the naphthalene 

 brought to boiling. The vapor was temporarily condensed by the air 

 cooling-coil, the bomb and carriage introduced, and the naphthalene again 

 boiled until the Beckmann thermometer showed a constant temperature 

 nearly equal to the boiling-point of pure naphthalene at the prevailing 

 atmospheric pressure. At the same time the resistance of the upper 

 electrode was measured, showing how full the bomb had become and 

 also showing whether any leakage was taking place. After the nine 

 readings of resistance were made at 218, the vapor was condensed, and 

 the bomb removed and cooled to room temperature before a fan. The 

 measurement at 18 was then repeated to find out whether any change had 

 occurred in the solution. The same procedure was followed at 306, 

 except that, in order to avoid loss of benzophenone, the bath was not 

 heated before introducing the bomb. The experiments at 306 were all 

 made after the work at 218 had been completed. 



The temperature in the 18 bath was kept constant within 0.01, and 

 was measured with a Beckmann thermometer. This was compared at 

 various points in the neighborhood of 18 with a Baudin thermometer 

 (No. 15958) which had been standardized by the Bureau of Standards at 

 Washington. The corrected temperatures of the standard are referred 

 to the hydrogen thermometer. At 218 the difference in temperature 

 between the vapor-bath and a calibrating bath containing pure naphthalene 

 was determined by means of a Beckmann thermometer. 



The naphthalene used in the calibrating bath was obtained by recrys- 

 tallizing the purest Kahlbaum preparation once from absolute alcohol ; 

 that the original substance is pure is shown by the fact that the recrys- 

 tallized material did not differ more than 0.01 from the original in 

 boiling-point. The 218 point on the Beckmann thermometer was deter- 

 mined in the calibrating bath after every second heating by reference 



