Chemists can compute the ideal energy yields of even quite complex fuel and oxidizer molecules. But it’s quite another thing to realize ideals in practice. Some fuels, such as powdered aluminum, burn too slowly to react completely before they leave the nozzle. Others failed to meet the services’ standards for storability or low freezing temperatures. Some compounds slowly deteriorated over time, generating gas that could burst storage containers. Little by little, useful combinations were discovered, but the exotic promise of super fuels kept research going, trying to create ultra-high-energy combinations based on boron, fluorine (it eats through glass), and even remarkably poisonous mercury. Standards were created to measure sensitivity; some fuels, especially monopropellants, detonated if poured, or if they touched dust, or from micro-cavitation. Countless thousands of compounds were proposed, produced in labs, tested, and, if possible, fired in research rocket engines. Micro-contamination of containers by trace elements led to terrible surprises. Researchers were injured or killed.