Tissue Salt No.4 - Ferrum PhosphoricaTissue Salt No. 4 Ferrum Phosphorica is the constitutional Tissue Salt for Birthdates February 20 to March 21. The long term Biochemic approach is augmented by supplying the Bridge Salts corresponding to the months between birth retrograde to the time of conception, which may include Kalium Phosphorica, Natrium Sulphuricum & Kalium Muriaticum for those with Ferrum Phosphoricum as their Constitutional Salt.