Note 37 — Chapter XXII · IRON, COBALT, AND NICKEL

Prior to Fortmann, Rousseau (1889) endeavoured to solve the question as to whether CoO2 was able to combine with bases. He succeeded in obtaining a barium compound corresponding to this oxide. Fifteen grams of BaCl2 or BaBr2 are triturated with 5–6 grams of oxide of barium, and the mixture heated to redness in a closed platinum crucible; 1 gram of oxide of cobalt is then gradually added to the fused mass. Each addition of oxide is accompanied by a violent disengagement of oxygen. After a short time, however, the mass fuses quietly, and a salt settles at the bottom of the crucible, which, when freed from the residue, appears as black hexagonal, very brilliant crystals. In dissolving in water this substance evolves chlorine; its composition corresponds to the formula 2(CoO2)BaO. If the original mass be heated for a long time (40 hours), the amount of dioxide in the resultant mass decreases. The author obtained a neutral salt having the composition CoO2BaO (this compound = BaO2CoO) by breaking up the mass as it agglomerates together, and bringing the pieces into contact with the more heated surface of the crucible. This salt is formed between the somewhat narrow limits of temperature 1,000°-1,100°; above and below these limits compounds richer or poorer in CoO2 are formed. The formation of CoO2 by the action of BaO2, and the easy decomposition of CoO2 with the evolution of oxygen, give reason for thinking that it belongs to the class of peroxides (like Cr2O7, CaO2, &c.); it is not yet known whether they give peroxide of hydrogen like the true peroxides. The fact that it is obtained by means of iodine (probably through HIO), and its great resemblance to MnO2, leads rather to the supposition that CoO2 is a very feeble saline oxide. The form CoO2 is repeated in the cobaltic compounds (Note 35), and the existence of CoO2 should have long ago been recognised upon this basis.