aqueous solution reacted with a mineral acid e g phosphorous acid with water being added as necessary to adjust specific gravity the metal hydroxide solution is pumped into port 20 of the cross pipe tee 10 the mineral acid is pumped to port 30 and the water is pumped into port 40 reaction begins on contact of the metal hydroxide solution and mineral acid and the mixture of the reactants is forced substantially immediately into the static in line mixer 50 where reaction continues to occur the rate of total feed is controlled so that the temperature as taken about midway up the pipe 60 above the in line mixer 50 is maintained at a desired level and preferably at about 300 degrees f u2212 0 50 degrees generally speaking the reaction continues in the pipe 60 since the reaction of the present invention is exothermic external heat need not be supplied to the system as a general practice i simply measure the temperature about one half way up the distance of the pipe 60 as shown in the fig1 by temperature indicator 130 however the temperature could easily be measured anywhere between the cross pipe reactor and discharge into the receiving tank 70 as shown in fig1 the ratio of the potassium hydroxide solution to phosphorous acid fed is adjusted to.