A new crystal of aluminium pyrophosphate 18-hydrate, Al₄(P₂O₇)₃⋅18H₂O, was obtained by double decomposition from mixed aqueous solution of ammonium phosphate and ammonium alum in the pH range below 2.5. In the pH range 3-6, two different crystals of aluminium orthophosphates (A-type and B-type) AlPO₄⋅2H₂O, whose structures remain unknown, were obtained. The pure A-type crystal was able to be crystallized by this method, while the B-type was always acompanied by the A-type. We found that the pure B-type can be crystallized by autoclave treatment on amorphous precipitate from the mixed solution under the pressure of 10 atm. at 182°C. The physical and chemical properties of these new crystals were studied.
When aluminium orthophosphate crystals (A-type and B-type) were heated they became amorphous anhydrites after missing their crystallization water near 200°C. At about 400°C they changed directly to tridymite form AlPO₄ without passing quartz-form AlPO₄ (berlinite) even if no alkali existed at all, and holding for 2 weeks in the stable temperature range of berlinite caused no inversion to berlinite. The amorphous anhydrites changed also to cristobalite- form AlPO₄ at about 800°C. These cristobalite-form AlPO₄ obtained at relatively low temperatures had imperfect structures having enlarged lattice spaces.
The extra pure cristobalite-form AlPO₄ obtained by heating aluminium orthophosphates above 1, 350°C, did no more invert to tridymite-form or quartz-form AlPO₄, but with alkalis coexisted these inversions were able to take place smoothly.
Aluminium pyrophosphate crystal lost its crystallization water at about 180°C, and at a little higher temperatures some P₂O₅ vapourized from the amorphous anhydrate, which decomposed to aluminium metaphosphate Al(PO₃)₃ and cristobalite-form AlPO₄. At above 1, 050°C more vapourisation of P₂O₅ and decomposition of metaphosphate to cristobalite-form AlPO₄ occured.
On heating the pyrophosphate a new phase appeared prior to the metaphosphate and this coexisted with the metaphosphate and cristobalite-form AlPO₄ up to about 1, 000°C.

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Wettabilities of various refractories by two kinds of carbon steel were determined at 1550°C in N₂ atmosphere by sessile drop method using a heating microscope. Samples from stabilized zirconia, zircon, magnesia, alumina, high-alumina, fireclay, silica and magnesiachrome refractories were served to the test. Stabilized zirconia was found the least wettable and aluminous refractories the most.
Discussions on the correlation between wettability and chemical composition of refractories were given. The effects of surface conditions and reactions between steel and refractory on the wettability was also discussed. Several cases which are actually observed in steel plant refractories and with which the wetting properties have close relation were explained.
These wetting tests may also be applied to evaluate the corrosion resistance of refractories against molten steel.

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