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applicable only to explosives which detonate. Black powder and other explosives which burn producc but little effect, for the gases blow out the stemming and escape. The test is largely one of brisance, but for explosives of substantially equal brisance it gives some indication of their relative power. An explosive of great brisance but little power will create an almost spherical pocket at the bottom of the hole in the block, while one of less brisance and greater power will enlarge the hole throughout its

Figure 13. Lead Block Tests (above), and Trauzl Tests (below). (Courtesy U. S. Bureau of Mines.)

length and widen its throat at the top of the block. The form of the hole, then, as shown by sectioning the block, is not without significance. The Trauzl test does not give reliable indications with explosives which contain aluminum (such as ammonal) or with others which produce very high temperatures, for the hot gases erode the metal, and the results are high. A small Trauzl block is used for testing commercial detonators.

Another test, known as the small lead block test, is entirely a test of brisance. As the test is conducted at the U. S. Bureau of Mines, a lead cylinder 38 mm. in diameter and 64 mm. high is set upright upon a rigid steel support; a disc of annealed steel

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