area such as flakes or by flattening the spherical granules. Drying is usually performed under a vacuum. The solvents are condensed and recycled. The granules are also coated with graphite to prevent static electricity sparks from causing undesired ignitions. Smokeless powder does not leave the thick, heavy fouling of hygroscopic material associated with black powder that causes rusting of the barrel (though some primer compounds can leave hygroscopic salts that have a similar effect; non-corrosive primer compounds were introduced in the 1920s).) Faster-burning propellants generate higher temperatures and higher pressures, however they also increase wear on gun barrels. Nitrocellulose deteriorates with time, yielding acidic byproducts. Those byproducts catalyze the further deterioration, increasing its rate. The released heat, in case of bulk storage of the powder, or too large blocks of solid propellant, can cause self-ignition of the material. Single-base nitrocellulose propellants are hygroscopic and most susceptible to degradation; double-base and triple-base propellants tend to deteriorate more slowly. To neutralize the decomposition products, which could otherwise cause corrosion of metals of the cartridges and gun barrels, calcium carbonate is added to some formulations. To prevent buildup of the deterioration products, stabilizers are added. Diphenylamine is one of the most common stabilizers used. Nitrated analogs of diphenylamine formed in the process of stabilizing decomposing powder are sometimes used as stabilizers themselves. The stabilizers are added in the amount of 0.5–2% of the total amount of the formulation; higher amounts tend to degrade its ballistic properties. The amount of the stabilizer is depleted with time. Propellants in storage should be periodically tested for the amount of stabilizer remaining, as its depletion may lead to auto-ignition of the propellant. Composition Currently, propellants using nitrocellulose (detonation velocity , RE factor 1.10) (typically an ether-alcohol colloid of nitrocellulose) as the sole explosive propellant ingredient are described as single-base powder. Propellants mixtures containing nitrocellulose and nitroglycerin (detonation velocity , RE factor 1.54) as explosive propellant ingredients are known as double-base powder. Alternatively diethylene glycol dinitrate (detonation velocity , RE factor 1.17) can be used as a nitroglycerin replacement when reduced flame temperatures without sacrificing chamber pressure are of importance. Reduction of flame temperature significantly reduces barrel erosion and hence wear. During the 1930s, triple-base propellant containing nitrocellulose, nitroglycerin or diethylene glycol dinitrate, and a substantial quantity of nitroguanidine (detonation velocity , RE factor 0.95) as explosive propellant ingredients was developed. These "cold propellant" mixtures have reduced flash