Practically every class and every grade of commercial explosive are used in open-air work to meet varying conditions. In breaking down rock in quarries the explosives generally employed are: Black blasting powder, granulated nitroglycerin powder containing 5 to 15 per cent of nitroglycerin, straight nitroglycerin dynamites con taining 15 to 60 per cent of nitroglycerin, low-freezing dynamites commercially rated according to the equivalent percentage of strength of the straight nitroglycerin dynamites, and ammonia dynamites rated in a similar way. In recent years blasting gelatin, gelatin dynamites, ammonium-nitrate powders containing nitro substitution compounds, chlorate powders, and the se-called nitro starch powders have been used to a small extent in quarry work.