22 February 1954

Dr. Donald T. Wagman

National Bureau of Standards

Washington 25, D.C.

Dear Dr. Wagman:

I am writing to ask about a value in Circular of the National Bureau of Standards 500; namely, the value given for the enthalpy of atomic boron.

On page 13 the enthalpy of atomic boron at 25° C is given as 97.2 kcal/mole. On page 939 the only specific reference for this value is Footnote 2, which reads "2. Calculated."

I have recently been making another effort to decide between the high value and the low value for the heat of sublimation of graphite, and in the course of this work I made a prediction of the heat of sublimation of boron. My predicted value for boron is 126.3 kcal/mole. This is not much different from the value 115 given in 1936 by Bichowsky and Rossini. They say in their book that the value is based upon their estimate of the heat of vaporization of boron.

My value is, however, considerably larger than the value 97.2 given in the Bureau of Standards Bulletin. The fact that your value is recorded to 0.1 kcal/mole suggests that it is more than an estimate. I shall be grateful to you for information on this point, and for your advice as to how much weight I should place on the Bureau of Standards value.

I notice that a considerable number of values have the same specific reference - the designation as calculated. I have not found a statement in the Bulletin about the significance of these values; perhaps you can point it out to me, or tell me what significance should in general be given to them.

With thanks, I am

Sincerely yours,

Linus Pauling:W