1. A METHOD OF MANUFACTURING SILICON NITRIDE POWDER PRDOMINANTLY IN THE A-PHASE BY REACTING SILICON POWDER WITH A NITRIDING ATMOSPHERE AT AN ELEVATED TEMPERATURE BELOW THE MELTING POINT OF THE SILICON POWDER, WHICH COMPRISES PROVIDING THAT, PRIOR TO NITRIDING, THE SILICON POWDER INCLUDES A COMPOUND WHICH IS IN THE SOLID PHASE AT SAID ELEVATED TEMPERATURE AND WHICH CONTAINS OXYGEN WHICH WILL TAKE PART IN THE NITRIDING REACTION, THE AMOUNT OF SAID COMPOUND BEING SUCH THAT THERE IS PRESENT IN THE SILICON POWDER BETWEEN 1.4% AND 2.5% BY WEIGHT OF REACTABLE OXYGEN.