582 



A statistical study of the results showed fvirther that the per cent 

 differences between the reading of the two gauges in a given block were 

 not significantly different for the light and heavy blocks. In other 

 words, the reproducibility of results was not affected by the weight of 

 the mountings over the range of conditions employed. 



5. Miscellaneous Experiments 



(a) Increased damage to diaphragm gauges placed above the charge 

 and its explanation in terms of bubble pulses . It was foimd that xmder 

 certain circumstances at UERL damage gauge recorded from 10 to 80^ 

 greater damage when mounted vertically above a small charge than when 

 mounted at the same level to the side, the charge being at the same depth 

 in the two experiments. This result immediately suggested that the 

 secondary pulses from the rising gas bubble were causing extra damage. 

 Therefore, a contact was placed in the gauge above the charge to measure 

 the time required for final deformation. This time iras found to be very 

 great, approximately 250 msec, much greater than the time previously 

 reported for the gauge in the same horizontal plane as the charge 

 (Section V, k, c). Furthermore, calcxilation showed that the time ob- 

 served for the over -the -charge case corresponded closely with the expected 

 time of arrival of the third wave from the explosion (i.e., the second 

 bubble pulse) and that the center of the bubble at this time shoiLLd have 

 risen practically to the gauge itself. 



The data for these experiments are summarized in Table XXI. Gaioges 

 were mounted in the usiml manner on a steel ring, which was, however, 

 suspended with its plane vertical instead of horizontsLL. The charge was 

 cylindrical with its axis horizontal, i.e., perpendiciilar to the plane 

 of the ring. It was found that the increased damage occurred only when 

 the line from the charge to the gauge was within 10° or so of the vertical. 

 The contour of the damaged diaphragm was rounder than usual and the ring 

 was considerably distorted near the top gauge, with bad damage to the 

 gauge moimting bracket. 



The time of maximum damage was measiored with the contact oscillograph 

 technique (Section V, kc) in another set of tests. A gauge was mounted 

 k-2 in. above a charge of 200 gm. loose tetryl. Lot k steel diaphragms 

 were used. The charge depth was 12 ft. A second damage gauge was used 

 as a control in two of the shots, the line from it to the charge making 

 an angle of 36° with the vertical. The damage to the gauge above the 

 charge was quite variable, making it difficult to get many results on the 

 time of maximum damage. 



The results which were obtained are listed in Table XXII. 



Figure 27 shows the results of an approximate calculation of the 

 bubble period, radius, and rise xinder gravity. This is based on 

 Bancroft ' sz_/ maocimum radius measurement for 50 gm. tetryl at a depth . 

 of 10 ft., the observed pulse time for 200 gm. tetryl at a depth of 11 ft_5/ 



2^/ Division 8, NDRC, OSRD, Interim Report UE-b, p.l3. 

 25/ Ibid., UE-11, p. 7 



