Published physical data on aureomycin and Terramycin and the results of studies on the structure of Terramycin require a relationship between these compounds expressed by structures I and II, respectively. The structure I is consistent with analytical data for aureomycin (C22H23N2O8Cl). The naphthacene skeleton in aureomycin is demonstrated by reduction to desdimethylaminodesoxyaureomycin (III) and acid dehydration to a red compound yielding naphthacene via zinc dust distillation. Aureomycin's ultraviolet absorption spectrum and acidity constants (pKa's 3.4, 7.4, 9.2) are similar to Terramycin's (pKa's 3.5, 7.6, 9.2), indicating a common polycarbonyl system; the longer wavelength absorption of aureomycin is due to an aromatic chlorine atom (position confirmed by isolation of 5-chlorosalicylic acid and 5-chloro-7-hydroxy phthalides). Desdimethylaminodesoxy compounds from both antibiotics have similar absorption spectra, with shifts due to removal of the C6 hydroxyl group. A C14-hydroxyl in aureomycin is shown by alkali-induced rearrangement of III to phthalide IV (analogous to Terramycin's V). Pyrolysis of IV and V yields respective phthalides, supporting ring system similarity. All oxygens in aureomycin are placed; aureomycin differs from Terramycin by a C16 chlorine atom and absence of a C12 hydroxyl group. Both share structure A (named tetracycline), with Terramycin as oxytetracycline. The ever-increasing importance of condensed phosphates and polyelectrolytes combined with inadequacies in published phosphate hydrolysis data necessitated a fundamental research program. Condensed phosphates hydrolyze in aqueous solutions to less condensed phosphates and ultimately orthophosphate. Hydrolysis rate depends on temperature, pH, concentration, and ionic environment (affecting via complexation and ionic atmosphere). Tetramethylammonium tripoly- and pyrophosphates were hydrolyzed in 10% tetramethylammonium bromide and water; sodium analogs in sodium bromide (same ionic strength). pH was controlled (1, 4, 7, 10, 13) and temperatures held (30, 60, 90, 125°); concentration adjusted to give 1% orthophosphate on complete hydrolysis. Degradation follows first-order kinetics. Unlike sodium tripolyphosphate (minimum rate at pH 10), tetramethylammonium phosphate hydrolysis rate decreases with increasing pH (1-13). Temperature dependence follows the Arrhenius equation (k = Ae⁻ᴱ/ᴿᵀ), with frequency factor and activation energy varying with pH (Figs. 1-2).