Abstract: Calcined alkali phosphates of high citrate solubility are made by subjecting natural calcium phosphates including tricalcium phosphate to a thermal decomposition with an aqueous alkali hydroxide solution in a revolving furnace at 900.degree. to 1300.degree.C in the presence of silicic acid. The amounts in the starting mixture are selected to provide for one mol of P.sub.2 O.sub.5 per 1.1 to 1.5 mol of Me.sub. 2 O (Me being an alkali metal) and an amount of silicic acid sufficient to form calcium orthosilicate by combining with 1 mol of CaO derived from the initial tricalcium phosphate and with the lime which is not part of a phosphoric acid compound. The alkali hydroxide solution is introduced at a 30 to 80% concentration directly into the revolving furnace so as to cause the solution to impinge upon the mass while the same is at a temperature of at least 400.degree.C.

Abstract: An air outlet valve for a diving apparatus includes a housing having an inlet and an outlet spaced from the inlet with a flow passage between the outlet and inlet having interior annular valve seat defined across the flow path. An axially extending actuation member is journalled in the housing for axial displacement and it includes an outside knob portion at one end and an inside knob portion at the opposite end which may be engaged for moving the actuation member. A flexible diaphragm which has an annular sealing rim portion which engages on the valve seat is secured at its central portion to a shaft portion of the actuation member and the sealing rim portion is engageable on the valve seat to close the flow passage.