is 1 09 1 40 and the ratio li 2 o li 2 o na 2 o k 2 o is 0 98 in terms of mechanical properties the compositions of table 6 have a fiber density of 2 371 2 407 g cm 3 and an average fiber tensile strength or fiber strength of 3730 4076 mpa the fiber tensile strengths for the fibers made from the compositions of table 6 were measured in the same way as the fiber tensile strengths measured in connection with the compositions of table 5 the fibers formed from the compositions were found to have young 39 s modulus e values ranging from 73 84 81 80 gpa the young 39 s modulus e values for the fibers were measured using the sonic modulus method on fibers elastic modulus values for the fibers drawn from glass melts having the recited compositions were determined using an ultrasonic acoustic pulse technique on a panatherm 5010 instrument from panametrics inc of waltham mass extensional wave reflection time was obtained using twenty micro second duration 200 khz pulses the sample length was measured and the respective extensional wave velocity v e was calculated fiber density u03c1 was measured using a micromeritics.