Cyrias Ouellet

An Investigation of Adsorbed Films by Means of a Photoelectric Counter

A photoelectric tube counter of special design has been used for investigating adsorbed layers on a gold surface. The high sensitivity of the counter allows accurate measurements of photoelectric thresholds to be made with continuous ultraviolet light from a source of moderate intensity. The variation of the work function φ with the amount of adsorbed material can thus be followed quantitatively and continuously. The formation of gold oxide layers proceeds over definite steps with increases of 0.35 volt in the work function. The adsorption of iodine is reversible and the resulting increase in the work function varies with the iodine pressure according to a Langmuir isotherm, the saturation value being Δφ = +0.21 volt. The adsorption of ethyl alcohol is also reversible, but gives rise to a double threshold, suggesting the existence of liquid islands on the gold surface.

A Photoelectric Investigation of the Cool Flame of Ether

A method is described, in which the light from a cool flame under the form of a static, uniform glow is measured as a function of time by means of a multiplier photo‐tube and a single‐sweep cathode‐ray oscillograph. The circuit embodies an a.c.—d.c. amplifier and a slow sweep. Cool flames of diethylether‐oxygen mixtures in a Pyrex cylinder 4.6 cm in diameter have been studied under the following range of conditions: 180–250°C, 0–150 mm and 5–95 percent ether. The pulsating glow, which lasts about 1 second, shows two and sometimes more maxima. The generally accepted lower pressure limits appear as regions of feeble but smoothly decreasing intensities. Under the conditions of our experiments, the temperature coefficient is negligible. Both intensity and integral emission increase regularly with the concentrations of the reactants and are maximum at 50 percent ether by volume, the variations being roughly symmetrical with respect to the partial pressures of either component. Variations of pressure and composition cause regular but considerable changes in the shapes of the oscillograms. Light and pressure pulses follow each other closely, suggesting that the latter are of mainly thermal origin and that the light intensities reflect the instantaneous reaction rates. The glow lasts longer in the wider vessels. In the presence of the reaction products, it either fails to appear or emits the normal amount of light. A preliminary analysis of the quantitative data is given and possible interpretations, in terms of oxidation mechanisms, are discussed.

Limits of slow combustion and explosion for ketene-oxygen mixtures

The behaviour of stoichiometric ketene-oxygen mixtures (CH2CO:2O2) was studied for initial temperatures and total pressures ranging from 280° to 440°C and from 50 to 250 mm of mercury. Limits of slow combustion, cool flames and explosion were determined. The products of incomplete slow combustion were essentially carbon monoxide, carbon dioxide and acetic acid.

On the gas-phase oxidation of carbon suboxide and monoxide

The combustion of C 3 O 2 was studied in a Vycor cylinder 30 cm long and 4 cm in diameter, in the ranges 20–500 mm Hg and 560°–680°C. For 1 C 3 O 2 :2 O 2 mixtures, the lower explosion limit ( P l =250 mm at 680°C) lies well above the upper explosion limit for CO−O 2 mixtures up to 653°C, where both limits intersect. Below the lower explosion limit for C 3 O 2 −O 2 , slow oxidation of C 3 O 2 sets in without delay and the pressure rise corresponds in all cases to the over-all change C 3 O 2 +2 O 2 =2 CO+CO 2 +O 2 . When practically all the C 3 O 2 is consumed, oxidation of CO sets in abruptly. It is explosive at pressures below the CO−O 2 upper pressure limit; it proceeds with a gradual pressure decrease at pressures above the CO−O 2 upper limit, but below the C 3 O 2 −O 2 lower limit. The rate of the slow oxidation of CO above its upper limit is found to be independent of the CO concentration over the range 60–120 mm Hg, and inversely proportional to the square of the CO 2 concentration. During the slow oxidation of C 3 O 2 , the ratio CO/CO 2 is constantly equal to 2, indicating that the propagation takes place according to C 3 O 2 +O→C 2 O+CO 2 C 2 O+O 2 →2 CO+O. The apparent orders for “dry” mixtures are 2 in C 3 O 2 and 1/2 in O 2 . Addition of 1% H 2 O accelerates the reaction and brings the explosion limit for C 3 O 2 −O 2 downward by about 150 mm and 180°C. The temperature coefficients of both the lower limit for C 3 O 2 −O 2 and the upper limit for CO−O 2 lead to the same value E ⋍28 kcal mole −1 for the branching reaction, which we believe to be CO 2 * +O 2 →CO 2 +O+O. The effects of C 3 O 2 and of CO on each others oxidation can be accounted for by competition for the O atoms produced in the above reaction.