The study of the absorption properties of slow neutrons establish the existence of absorption bands which correspond to energy intervals sufficiently narrow to allow one to isolate relatively homogeneous neutron groups. In this work, we describe several experiments and considerations designed to disclose the characteristics of the absorption and scattering properties of the various groups. Summary: 1. Introduction. 2. Measurements and their reduction. 3. Selective absorptions. 4. Slow neutron groups. 5. Systematic absorption measurements. 6. Albedo. 7. Scattering of the neutrons of a single group. 8. Mean free path of thermal neutrons. 9. Groups as a function of the distance from the source; energy ratios. 10. Passage of the neutrons from one group to another. 11. Behavior of the groups in the neighborhood of the surface of the paraffin. 12. Width of the energy bands corresponding to the groups. Total number of neutrons. 13. Summary and discussion.