492 



BELL SYSTEM TECHNICAL JOURNAL 



The cold flow test is specially designed to note the distortion of 

 materials which in service are under pressure, such as spring pileups, 

 inserts and apparatus in the form of banks and terminal blocks. The 

 specimen which is 3/^ X 3^ X 3^" in size is first conditioned at 150° F. 



Fig. 6 — Impact machine. 



for 4 hours and then to 90 per cent R.H. and 85° F. for 68 hours to 

 permit absorption of moisture. It is then held under 4000 lbs. per 

 square inch for 24 hours at 120° F. i 1° and the percentage change in 

 thickness determined. 



