The oxalic acid project

To examine the reliability of X-ray charge densities at a time of rapid development of new methods, the Commission on Charge, Spin and Momentum Densities of the lUCr organized a project under which a single substance, a-oxalic acid dihydrate, was studied in a number of laboratories using X-ray, neutron, and theoretical methods. The report by Coppens on the study, published in 1984, established unequivocally the qualitative reproducibility of chemically significant features in deformation density maps, which had not been generally accepted. 

With the more widespread use of subnitrogen cryogenic temperatures, use of smaller samples made possible by brighter sources, and rapid developments in detector technology and computational methods, the conclusions of the oxalic acid project are now of mainly historical importance. However, the project remains an example of the value of collaborative efforts in establishing the validity of a scientific method. 

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