The d-d band is only weakly structured in these complexes, but in some cases three components are distinguishable corresponding to transitions from the manifold of filled d orbitals of Figure 6 to the u* orbital of xy symmetry. The u interaction between the xy and zz d orbitals with the ligand u orbitals could be the same in the green and the orange complexes. Then the difference in the d-d absorption maximum for the two groups of complexes would be determined by 'a different amount of interaction between the yz, z x d orbitals and the ligand a orbitals. The most important interaction will be with the lowest lying empty a* orbital which stabilizes the d, orbitals. The stabilization must be most pronounced in the complexes having an even number of ligand ?r orbitals only half filled, Le., in the green complexes. We would therefore expect the d-d transitions in the green complexes to occur at a higher energy than in the orange complexes. The opposite is observed, and we interpret this as an indication of significantly different u interactions in the two groups of complexes. This effect is not evident from the variation of bond lengths.Acknowledgment. The authors are grateful to Dr. K. Schaumburg for measuring 270-MHz spectra and for taking part in discussions of the results and to Mr. F. Hansen for excellent technical assistance.

Data published in the 1957 Romanoff National Bureau of Standards report for the corrosion of steels buried in soils for up to 17 years are re-interpreted using the bi-modal model for corrosion in wet environments. The relevant soil properties are those of the backfill, not those of the undisturbed soil at the depth of the steel samples. Using estimated backfill properties shows that stiff clays, calcareous loams and gravelly loams corrosion transitioned from Mode 1 to Mode 2 after 4-8 years, following severe corrosion and deep pitting. For most other backfill soils, the transition occurred later and corrosion was less severe. These differences are attributed to the relative influence of differential aeration and localised corrosion caused by air-voids at the soil-metal interface. The declining rate of corrosion in the later part of Mode 2 is attributed to backfill consolidation decreasing the diffusion of oxygen and possibly also of moisture.

In einer fruheren Veroffentlichung(') wurde fur 64 Sprengstoffe vom Ideal-CHNO-Typ eine einfache lineare Beziehung aufgestellt zwischen der Detonationsgeschwindigkeit bei theoretisch maximaler Dichte und einem Faktor F, der nur abhangig ist von der chemischen Zusammensetzung und der Struktur der Sprengstoffe. Auf der Grundlage expenmenteller Daten fur 9 fluorhaltige Sprengstoffe wurde nun die Gleichung zur Berechnung des Faktors erweitert unter Einfugung zusatzlicher Glieder fur Fluorverbindungen. Aufjerdem wurde die Zuverlassigkeit der linearen Beziehung noch einmal uberpriift fur sieben bereits fruher veroffentlichte experimentelle Daten der Detonationsgeschwindigkeit von Sprengstoffen von CHNO-Typ. Die berechneten Werte der Detonationsgeschwindigkeit fur alle 16 Sprengstoffe liegen rnit einer Abweichung von 6 % im Bereich der experimentallen Werte, der absolute Fehler betragt k 3%.Prkvision de la vitesse de dktonation des explosifs partir de leur composition et de leur structure Dans une publication antCrieure(') on a indiqut pour 64 explosifs du type ideal CHNO une relation lintaire simple entre la vitesse de dktonation pour une densitt thtorique maximale et un facteur F qui ne dtpend que de la composition chimique et de la structure de l'explosif en question. Sur la base de donntes exptrimentales acquises avec 9 explosifs contenant du fluor, on a ttendu la formule permettant de calculer le facteur F en y ajoutant des termes supplkmentaires pour les composts fluorts. En outre, on a a nouveau vCrifit la validitt de la relation lintaire en la controntant aux donntes exptrimentales puhlites rkcemment et concernant 7 explosifs du type CHNO. Pour l'ensemble des 16 explosifs, les valeurs calculkes pour la vitesse de dttonation concordent 2 1 6% prks avec les valeurs exptrimentales, l'erreur absulue &ant de f 3%.

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