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The semiconductivity and photoconductivity of the solid free radicals galvinoxyl(2,6-di-tert-butylcc(3,5-di-tert-butyl-4-oxo-2,5-cyclohexadien-l-ylidene) p-tolyloxy radical) and DPPH (a,a-diphenylp-picryl hydrazyl) and related compounds have been examined. Their behaviour is similar to that of diamagnetic poly-cyclic hydrocarbons. They show semi-conducting properties with energy gaps in the range 1-4-1.6 eV whether as single crystals, films or compressed powders. In sandwich cells the photocurrent follows the absorption spectrum, except for the lowest energy band where no significant photocurrent is observed.

This paper is based on measured environmental condi tions and ventilation rates during a summer period in the occupied naturally ventilated and passively cooled Envi ronmental Building at the Building Research Establish ment, Garston, UK. Initially, the comfort and air quality environmental conditions in the first (typical) floor of the building are discussed. These are found to be satisfacto ry. The paper then goes on to investigate the cooling effectiveness of the various ventilation flowpaths and associated thermal mass. In particular, the paper focuses on the south façade passive stacks and their relative con tribution to cooling through increased ventilation. It was found that due to the relatively narrow plan of the build ing, the cross-ventilation flow paths could satisfy most of the summer cooling ventilation requirements. Passive stacks can enhance the cooling ventilation of the space during warm and still days, as intended by the design, and may also have the potential to assist night-time cool ing due to their thermally massive structure.

Electronically excited lead atoms, Pb(6'Dz), have been generated by the pulsed irradiation of lead tetraethyl in the presence of helium buffer gas and monitored photoelectrically in absorption by time-resolved attenuation of atomic resonance radiation at A = 374 nm ( 7 ~( ~P ; ) c 6 p * ( ~D ~) ) . The decay of the excited atom in the presence of added gases has been investigated and rate constants for removal are reported for the following collision partners :