What is "microcrith"

Microcrith \Mi`cro*crith"\, n. [Micro- + crith.] (Chem.) The weight of the half hydrogen molecule, or of the hydrogen atom, at one time taken as the standard in comparing the atomic weights of the elements; thus, an atom of oxygen weighs sixteen microcriths. This unit is no longer used, and has been replaced by the Dalton, which is of approximately the same value. See molecular weight and Crith.
--J. P. Cooke.

n. (context physics obsolete English) The weight of the half hydrogen molecule, or of the hydrogen atom, taken as the standard in comparing the atomic weights of the elements.