The _nitrate_, Zr(NO₃)₄,5H₂O, separates from concentrated solutions of the oxide in nitric acid by evaporation over sulphuric acid and sodium hydroxide; it is believed to be a zirconylnitric acid, ZrO(NO₃)₂,2HNO₃,4H₂O by analogy with the sulphate. When its aqueous solutions are warmed, basic salts separate. Kolbe[468] has described an additive compound with antipyrine, Zr(NO₃)₄,6C₁₁H₁₂ON₂, which is soluble in water, and melts at 217°-218°. [468] _Zeitsch. anorg. Chem._ 1913, ~83~, 143. When phosphoric acid or a soluble phosphate is added to a solution of a zirconium salt, _zirconium phosphates_ of doubtful composition are thrown down; by fusion methods, various double phosphates have been prepared. A _hypophosphate_, Zr(PO₃)₂,H₂O, has recently been obtained by Hauser and Herzfeld[469] by precipitation. The same authors have prepared a _hypophosphite_, which is sensitive to light. When hypophosphorous acid, H₃PO₂, is added to a solution of zirconium nitrate, a precipitate is obtained, which dissolves in excess of the acid; by addition of alcohol to the clear solution, the hypophosphite, Zr(H₂PO₂)₄,H₂O, is thrown down in colourless, highly refracting prisms, which on exposure to sunlight for a short time become deep violet, without further perceptible change. [469] _Zeitsch. anorg. Chem._ 1913, ~84~, 92. _Zirconium carbonate_ has recently been obtained by Chauvenet.[470] Addition of sodium carbonate precipitates a basic orthocarbonate, ZrCO₄,ZrO₂,8H₂O, soluble in excess; when dried in vacuo, the precipitate loses water, forming the dihydrate, ZrCO₄,ZrO₂,2H₂O. When the latter compound is treated with carbon dioxide at a pressure of 30-40 atmospheres, the neutral orthocarbonate, ZrCO₄,2H₂O, is formed. When the compounds are heated, other basic salts are obtained. [470] _Bull. Soc. Chim._ 1913 [iv.], ~13~, 454. _Zirconyl oxalate_, ZrO,C₂O₄, is obtained in the hydrated form when oxalic acid is added to a zirconium salt in the presence of hydrochloric or acetic acid. It is a white powder, soluble in oxalic acid, and easily hydrolysed by water. If an aqueous solution of oxalic acid be saturated with zirconium hydroxide, an acid oxalate, ZrOH(HC₂O₄)₃,7H₂O, is obtained on evaporation. Double oxalates are readily obtained by dissolving zirconium hydroxide in solutions of alkali hydrogen oxalates, the general form being Zr(C₂O₄R´)₄,xH₂O. The _tartrate_ precipitated when tartaric acid is added to a zirconium salt in solution probably has the cyclic structure, COOZr(OH)₃ | CH--O | \ | Zr(OH)₂ | / CH--O | COOZr(OH)₃ as shown by the great rise in the specific rotatory power of solutions of alkali oxalates on addition of zirconium compounds. The precipitate dissolves readily in alkalies, and various double alkali tartrates have been prepared; the potassium salt, ZrO(C₄H₄O₆K)₂,3H₂O, is analogous to the thorium alkali tartrates. The solubility in alkalies is of great importance for the separation of iron and zirconium.