In the former case there is no later chance to remove sulphur, a minute quantity of which does great harm by leading to the formation of cementite instead of graphite and ferrite, and thus making the cast-iron castings too hard to be cut to exact shape with steel tools; in the latter case the converting or purifying processes, which are essentially oxidizing ones, though they remove the other impurities, carbon, silicon, phosphorus and manganese, are not well adapted to desulphurizing, which needs rather deoxidizing conditions, so as to cause the formation of calcium sulphide, than oxidizing ones.
Phosphoryl trifluoride, POF3, may be obtained by exploding 2 volumes of phosphorus trifluoride with 1 volume of oxygen (Moissan, 1886); by heating 2 parts of finely-divided cryolite and 3 parts of phosphorus pentoxide (Thorpe and Hambly, Jour.
It slowly reacts with cold water to form phosphorous acid; but with hot water it is energetically decomposed, giving much red phosphorus or the suboxide being formed with an explosive evolution of spontaneously inflammable phosphoretted hydrogen; phosphoric acid is also formed.
Hypophosphorous acid, HP(OH) 2, discovered by Dulong in 1816, and obtained crystalline by Thomson in 1874 (Ber., 7, P. 994), is prepared in the form of its barium salt by warming phosphorus with baryta water, removing the excess of baryta by carbon dioxide, and crystallizing the filtrate.
It is usually sent on the market in the form of sticks, which were at one time prepared by sucking the molten material up glass tubes; but the dangers to the workmen and other disadvantages of this method have led to its replacement by a continuous process, in which the phosphorus leaves the melting-pot for a pipe surrounded by water, in which it solidifies and can be removed as a continuous rod.
Next comes the deoxidizing and desulphurizing stage, of which the first step is to throw some strongly deoxidizing substance, such as coke or ferro-silicon, upon the molten metal, in order to remove thus the chief part of the oxygen which it has taken up during the oxidation of the phosphorus in the preceding stage.
In his researches, Roscoe showed that the atomic weight of the metal as determined by Berzelius and the formulae given to the oxides were incorrect, and pointed out that the element falls into its natural place in group V of the periodic classification along with phosphorus and arsenic, and not in the chromium group where it had originally been placed.
Kryst., 1894), in his researches on the tetragonal potassium and ammonium dihydrogen phosphates and arsenates, found that the replacement of potassium by ammonium was attended by an increase of about six units in the molecular volume, and of phosphorus by arsenic by about 4.6 units.
In some skin diseases such as psoriasis, chronic eczema and acne indurata, phosphorus is very useful, and cases of diabetes mellitus and lymphadenoma have improved under some of its compounds.
Orthophosphoric acid, H3P04, a tribasic acid, is obtained by boiling a solution of the pentoxide in water; by oxidizing, red phosphorus with nitric acid, or yellow phosphorus under the surface of water by bromine or iodine; and also by decomposing a mineral phosphate with sulphuric acid.