JOHN P. REDMOND
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linked monomers may alter their shape to achieve a more stable arrangement with their neighbors. This whole question becomes, "is the aggregate made up of native or denatured molecules?" This is an old question and one which is very difficult to answer. The present work has revealed the value of using ultracentrifugation along with any other technique for studying protein denaturation. The recognition of the aggregate in the heated solutions, particularly during the early stages of heating and with solutions in which very little turbidity (veronal, pH 8.5) or no turbidity (water, pH 7 ) arose has prevented the assignment of changes in such properties as viscosity, optical rotation,
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solubility and electrophoretic mobility to the formation of a new monomeric species. This technique is proving of real value too in work with other proteins and with other denaturing agents than heat. It may be that rather subtle configurational changes are involved in the actual "denaturation" of ovalbumin and that aggregation follows rapidly leading to the actual species which others have pictured as the one of different iiitramolecular configuration. Acknowledgments.-The author wishes to acknowledge the valuable technical assistance which Mr. Walter Gagen and Mr. James Smith provided to the experimental portion of this study.
KISETICS OF THE LOW PRESSURE NITROUS OXIDE DECORIPOSITTOS ON A PLATISUX FILAMENT1 BY JOHX P. REDMOXD A p p l i e d P h y s i c s Laboratory, T h e J o h n s H o p k i n s University, Silver S p r i n g , M a r y l a n d Received September I S , 1Q6W The decomposition of nitrous oxide on a platinum filament has been investigated over a pressure range of 0.02 to 4.0 mm. and a temperature range of 545 t o 820'. The reaction kinetics have been found to fit the LangmuirHinshelwood equation for a unimolecular decomposition with poisoning by atomic oxygen. The apparent activation energy is 32 f 1 kcal./mole. Added oxygen has the same poisoning effect on the reaction rate as the product oxygen. Nitric oxide is produced in small amounts during the decomposition a t the higher pressures. However, neither nitric oxide nor nitrogen has been found to poison the reaction.
Introduction Hinshelwood and Pritchard2 investigated the catalytic decomposition of nitrous oxide on platinum in the pressure region from 50 to 400 mm. and found the reaction velocity ( r ) to be represented by the equation
I n addition to the confusion in kinetics, there is also some question as to the nature of the adsorbed oxygen and the effect of added oxygen. The theoretical rate equation employed by Hinshelwood and Pritchard was derived on the basis of molecular oxygen adsorption, but Schwab and Eberlesa and Steacie and McCubbin8bhave r = k[X~Ol/'(l b[Ozl) (1) reported that the product oxygen was adsorbed as where 6 is a constant. This reaction is a classical exatoms. This atomic adsorption is in agreement with the lorn pressure kinetics of Cassel and Gluckauf. In ample of Langmuir-Hinshelwood kinetics for a unimolecular surface reaction with poisoning by a p r ~ d u c t . ~ addition, Steacie and McCubbin have studied the effect of added oxygen on the reaction rate. They applied However, this kinetic expression does not hold a t low their rate data to eq. 1 and found that added oxygen pressures (
