(1692) From the description and the experiments reported hereinafter it appears that the substance was white or ‘ yellow ’ phosphorus ( P4 ) .Even today phosphorus is always kept under water because , when exposed to the air , it slowly oxidizes to the fume - forming phosphorus pentoxide ( P2O5 ) .Phosphorus was discovered shortly before 1675 by the Hamburg chemist Hennig Brand , who sold the secret of its preparation to the German physician Johann Daniel Kraft .