<>N THF, DIFFUSION OF LIQUIDS. 



The experiment was conducted in the following way. The vessel 

 was just half filled with distilled water, and then placed on the spec- 

 trometer and the verticality of the reflecting faces carefully adjusted. 

 A glass tube drawn to a capillary in one end was introduced into the 

 vessel so that its lower end reached the bottom of the vessel. The 

 solution to be examined was poured very slowly, drop by drop, into 

 the tube until the vessel was full of liquid. In this way, the solution 

 was quietly made to occupy the lower half of the diffusion vessel. 

 The hole H was then closed, care being" taken to leave no air bubbles 

 within the vessel. The w T hole was left untouched about two or three 

 hours and then the measurement was made and repeated daily for 

 about a week without disturbing the vessel during that time. The 

 spectrometer and the cathetometer stood on a massive stone pier in a 

 small room, the temperature of which never varied by more than 2° C« 



§ 3. The relation between the concentration u of a salt solution 

 and its index of refraction n is almost linear. According to Schittt, (l) 

 the relation for NaCl solution is exactly linear. His result is given in 

 Table I., in which u is the number of grammes of NaCl in 100 gram- 

 mes of water, and n is the index of refraction for Xa-light at 18,°07 C. 



Table I. NaCl solution. 



(1) Schutt, Zeits. für phys. Chemie, 5. 1800. 



