Potassium Nitrate (KNO 3)
The oldest solid oxidizer used in high-energy mixtures, potassium nitrate (saltpeter) remains a widely-used ingredient well into the 20th century. Its advantages are ready availability at reasonable cost, low hygroscopicity, and the relative ease of ignition of many mixtures prepared using it. The ignitibility is related to the low (334°C) melting point of saltpeter. It has a high (39.6%) active oxygen content, decomposing at high temperature according to the equation
This is a strongly endothermic reaction, with a AH value of +75.5 kcal/mole of KNO 3 , meaning high energy-output fuels must be used with saltpeter to achieve rapid burning rates. When mixed with a simple organic fuel such as lactose, potassium nitrate may stop at the potassium nitrite (KNO 2) stage in its decomposition.
With good fuels (charcoal or active metals) , potassium nitrate will burn well. Its use in colored flame compositions is limited, primarily due to low reaction temperatures. Magnesium may be added to these mixtures to raise the temperature (and hence the light intensity), but the color value is diminished by "black body" emission from solid MgO. Potassium nitrate has the additional property of not undergoing an explosion by itself, even when very strong initiating modes are used.