We studied experimentally the condensation of Zn and Cu vapors from a high-temperature gas in an external weak constant magnetic field. We observed at all applied conditions, a chaotic time shift of the maximum of the size distribution function of dispersed particles. Simultaneously, a decrease in the width of the size distribution function of dispersed Zn particles from 40 nm (0 mT) to 10 nm (44 mT or 76 mT) was observed. The sizes of Zn particles were determined by laser probing. The sizes of dispersed Cu particles, determined by analyzing a substrate sample, were in the range of 10-400 nm without a magnetic field, and the range 30-320 nm in a magnetic field of 30 mT. The authors explain the observed results by arranging the dynamics of the spin pair of unpaired electrons of an atom from the gas phase and of an atom on the surface of a condensed particle in a magnetic field. Therefore, in a magnetic field, when an atom collides with a dispersed particle or condensation nucleus, the probability of creation of a singlet pair of spins of unpaired electrons is higher than that without a field.