Crystal growth in native collagen gels has been used to determine the role of extracellular matrix macromolecules in biological calcification phenomena. In this system, type I collagen gels containing sodium phosphate and buffered at pH 7.4 are overlayed with a solution containing CaCl2. Crystals form in the collagen gel adjacent to the gel-solution interface. Conditions were determined which permit the growth of crystals of hydroxyapatite [Ca10(PO4)6(OH)2]. At a Ca/P molar ratio of 2:1, the minimum concentrations of calcium and phosphate necessary for precipitation of hydroxyapatite are 10 mM and 5 mM, respectively. Under these conditions, precipitation is initiated at 18-24h, and is maximal between 24h and 6 days. Addition of high concentrations of chondroitin 4-sulphate inhibits the formation of hydroxyapatite in collagen gels; initiation of precipitation is delayed, and the final (equilibrium) amount of precipitation is decreased. Inhibition of hydroxyapatite formation requires concentrations of chondroitin sulphate higher than those required to inhibit calcium pyrophosphate crystal formation.

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Losses of mercury have been measured over a period of 220 days from paint films prepared from polyvinyl acetate emulsion (PVA), styrene/acrylic emulsion or alkyd gloss paints containing concentrations of mercury as phenyl mercuric acetate (PMA) from 0.005 to 0.16%. At all concentrations, simple PVA films lose mercury at lower rates than do comparable films prepared from PVA containing coalescing agent, or from styrene/acrylic emulsion.Mercury losses from alkyd gloss films are lower than those from other films at the lower mercury concentrations studied, but percentage loss rates for alkyd films increase somewhat with increasing mercury concentration. A simple explanation for this difference is offered in terms of physical structures of the paint films.