The lattice parameter versus composition curve has a newly discovered, and well defined, plateau extending from approximately 9.5 to 12 atom percent silicon. In addition, x-ray diffraction patterns were obtained from (100), (110), and (111) faces of each crystal. The room temperature lattice parameters of thirteen slowly cooled iron-silicon single crystals containing from 3.61 to 25 atom percent silicon were measured. The specific rate of protonation of MB/sup +/(T/sub 1/) by H/sub 2/PO/sub 4//sup -/ in water at pH 4.4 was found to be 4.5 +. 1 and from the kinetics of decay of triplet absorption to be 7.2. The pK/sub A/ of MBH/sup 2 +/(T/sub 1/) in water was determined from the dependence on pH of absorption at 700 and 825 nm to be 7.1/sub 4/ +. 720 nm confirms that the long-wavelength absorptions are due to different protonated states of the same species, MB/sup +/(T/sub 1/) and MBH/sup 2 +/(T/sub 1/). Observation of a pH-independent isobestic point approx. 19,000 M/sup -1/ cm/sup -1/ in 30% ethanol in water at pH 2. Long-wavelength T-T absorption in acidic solution is reported here for the first time: lambda/sub max/ approx. 13,200 M/sup -1/ cm/sup -1/ at pH 2 and lambda/sub max/ approx. Values found more » for these absorptions in the present work with 30% ethanol in water as solvent are lambda/sub max/ approx. Previously reported T-T absorption in the violet in acidic and alkaline solutions and in the near infrared in alkaline solution was confirmed. The absorption spectrum of T/sub 1/ dye was measured in different media at pH 2.0 and 8.2 by kinetic spectrophotometry. mu.M solutions of methylene blue in water, 30% ethanol in water or 50 v/v% water - CH/sub 3/CN at pH values in the range 2.0 - 9.3 converted the dye essentially completely to its T/sub 1/ state. Excitation by a Q-switched giant ruby laser (1.2 joule output at 694 nm, approx.
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