The rates of reaction of OH with propyne, but-l-yne, but-2-yne, pent-l-yne and hex-l-yne have been measured directly by using a discharge-flow resonance-fluorescence technique over a range of temperatures from 253 to 343 K. The room-temperature rate coefficients-are compared with previous determinations; the new values for pent-l-yne and hex-l-yne fit into a general pattern of reactivity consistent with a mechanism involving initial electrophilic attack of OH at the triple bond. Similar trends are also presented for other series of reactions between radicals and unsaturated organic molecules. The temperature dependences of the rate constants for the OH-talkyne reactions are small or negative, suggesting that adduct formation is the initial step in the reaction mechanism.

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The kinetics of the title reaction were investigated by molecular modulation-UV/visible absorption spectroscopy. NO3 and H 0 2 were generated by modulated photolysis of C12 in the presence of CION02, H2, and O2 in a flow system at 1 atm pressure and their concentration modulations monitored by time-resolved absorption at 662 and 220 nm, respectively. The rate coefficient for the overall reaction NO3 + H 0 2products, k4, was determined by computer fitting to data at five temperatures in the range 263-338 K and was given by k4 = ( 2. 3: : ; ) X lo-" exp(+(l70 & 270)/T) cm3 molecule-' s-l. An upper limit of 0.6 for the ratio k4,Jk at 283 K, where k4b is the rate constant for the reaction channel NO, + HOz -OH + NO2 + 02, was established by measurement of OH by modulated resonance absorption. The alternate channel, 4a, is assumed to produce HN03, Le., NO3 + H 0 2 -+ H N 0 3 + 02.

THE use of culture metlia of definite PiI concentration has suggested enquiries into the limiting and optimum zones for each bacterium. So far as the initial reaction of tlie medium is concerned, tliis has been a simple matter. But when it becomes necessary to determine the firial reaction of the niediani, to consider the composition of varying media, arid to allow for intervening conditions which favour or hinder growths, the probleni presents niany new aspects. Not the least among these, is the appearance of certain acids or salts as a direct result of the ruetabolisni of the inseminated organisms. In order to study the effects of these substances, it was thought worth while, therefore, to add minute quantities of different acids to certain media, so as to observe the early rate of growth of bacteria, under conditions which usually obtain oiily a t a later stage. To this end, an optirriuiri P, Concentration was determined for each strain in the presence of added acids. That such a series of observations would yield b a t crude firidirigs was fully appreciated: yet i t seemed possible that some of the unknown, and at present uncontrolled factors might be more clearly defined and openings he found for additional enquiry. After due consideration of the mass of work upon the phase of lag, etc., and an extended experience with the iiieasurerrient of growth by "opacity" methods, it was decided to approach the subject from the standpoint of total, or hourly, generations at the first maxinial period of growth. The Initial Reaction of IVediam and the Maximum Gvowth. Prior to the determination of the behaviour of bacteria under the conditions just laid down, it was evident that a preliminary survey should be made of the growth from the standpoint of the initial reaction of the culture medium. The expenses have been met by grants from the Medical Research Council, and the University of Bristol Colston Research Society. \Ye desire to acknowledge the painstaking and careful assistance rendered by X r F. Nichols.