414 



DILATOMETRIC METHODS 



employed, l)ut also in the fortunate fact that the measurements 

 may bo made without disturbing the system in any way. 



DILATOMETRIC APPARATUS AND ITS USE 



Gradient Tube. Tlu> glass gradient tube, that is employed to 

 furnish a ])ractically linear specific gravity gradient, has the form 

 and dimensions shown in Figure 150. The tube is mounted in a 

 thermostat that maintains its temperature constant to about 

 ±0.002"; the group at the Carlsberg Laboratory have done their 

 work at 30°. The tube is first filled with bromobenzene (sp. gr. 1.48) 



-T- 



E 



u 

 O 



Surface of 



water m 



thermostat 



6 cm 



-»-2.5cm. 



-»4-7 cm.-+* 



Fig. 150. The gradient tube. 



From Linderst r0m-Lan g 



and Lanz (1938) 



Fig. 151. Measuring micioscope. 



Frt)))t Linderst r()m-La7ig 



and Lanz (1938) 



up to the middle of the part connecting the two bulbs. After the 

 bromobenzene has attained the temperature of the bath, "water- 

 white" kerosene (sp. gr. 0.79) having the same temperature is added 

 carefully through a funnel fitted with filter paper to fill the remain- 

 der of the tube. The surface of the liquid in the tube should be below 

 that of the thermostat water. A long spatula is used to agitate gently, 

 for about 10 sec, the liquids in the region of their junction in the 

 middle of the tube so that some mixing will occur. After 24-48 hr. 

 the density gradient is sufficiently linear. Usually the gradient is 

 maintained for months and even years. 



