645 



composition of the charge, as given by the Hercules Company, is 13.5 grains 

 of pentaerythritol tetranltrate plus 0.^ grams of a 75/25 mixture of 

 diazodinitrophenol/potassium chlorate primer. In the calculation of 

 similarity curves, it was assumed that this corresponded to l.;iO grams of 

 a single explosive compound. It may or may not be correct but since the 

 same lot of caps was used throughout, the actual weight ussi.' does not 

 matter because no attempt was made to compare the absolute values of this 

 explosive with those of other explosives. 



The depth of the cap in each explosion was accurately located beneath 

 the surface of the water to + l/d/t in. by means of the support shown 

 In Fig. 3. Orientation of the cap was always the same with the axis of 

 the cap parallel with the axis of the camera and with the wire end towards 

 the camera. Water was allowed to flow slowly into the tank at all times 

 so that the water level was always the same, being regulated by overflow 

 over the edges of the tank. For the determination of the similarity 

 curve for these caps, single caps were fired, six at each of eight depths, 

 1/Ut 1/2, 1, 2, 3, U, 5, and 6 in. 



The sympathetic detonation series was executed in the following manner. 

 One cap (donor) was fired with its center exactly 3/4, in. from the center 

 of a second cap (acceptor), the axes of both caps being parallel with the 

 optical axis of the camera. Six shots ^rsre fired with the plane defined 

 by the axes of the caps parallel with the avirface of the water 

 (orientaticr A D ajid twelve witji this plane perpendicular to the surface 

 of the water. Of these twelve, six were fired with the donor charge below 

 (orientation A) and six with the donor charge above the acceptor (orientation D). 



D A 



The caps were separated 3/4 in. from center to center by taping them together 

 with accurately made 1/2 in, wooden separators and then taping both separator 

 and cap to the cap supoort. The depth of all these shots was 5 in. to the 

 center of gravity of the two caps which in the case of the vertical 

 orientation placed the center of the upper cap 4 5/8 in. below the surface. 



Surface active materials used were of three different types. For the 

 first twelve shots fired at depths of 4 and 3 in,, the tank contained a 

 solution made by dissolving 4 lb of a corimercial synthetic detergent 

 (marketed by the National Cooperative stores as "Synthetic Suds") in the 

 contents of the tank. This is probably a sulphonated oil derivative similar 

 to "Dreft". Mixed with the approximately 200 gallons of water in the tank, 

 this produced a solution whose surface tension was about 45.5 dynea/cm. 

 The second experiment was with first 5 lb and then 10 lb of Elmer and 

 Amend Company "Aerosol" 10% solution added to the contents of the tank. 

 This gave solutions with surface tensions of about 41 and 35 dynes/cm 

 respectively. To avoid excessive dilution of these solutions, the water 

 supply was not allowed to flow continuously but was only sufficient to 

 replace solution lost with each explosion. Because the surface tension- 

 concentration cun'oc for solutions of this type do not change very rapidly 

 in this concentration range, the change of surface tension with this 

 necessary dilution was slight. Samples were removed for analysis before 

 and after each explosion and surface tensions were measured with a Du Nouy 

 ring tensiometer manufactured by the Central Scientific Company, Caps 

 were fired at depths of 4, 8, and 12 in. for both of these concentrations 

 of "Aerosol", 



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