[48] Few compounds are known of the lower type PbX, and still fewer of the intermediate type PbX_{3}. To the first type belongs the so-called lead suboxide, Pb_{2}O, obtained by the ignition of lead oxalate, C_{2}PbO_{4}, without access of air. It is a black powder, which easily breaks up under the action of acids, and even by the simple action of heat, into metallic lead and lead oxide. This is the character of all suboxides. They cannot be regarded as independent salt-forming oxides, neither can those forms of oxidation of lead which contain more oxygen than the oxide of lead, PbO, and less than the dioxide, PbO_{2}. As we shall see, at least two such compounds are formed. Thus, for example, an oxide having the composition Pb_{2}O_{3} is known, but it is decomposed by the action of acids into lead oxide, which passes into solution, and lead dioxide, which remains behind. Such is red lead. (See further on.) [49] In the boiling of drying oils, the lead oxide partially passes into solution, forming a saponified compound capable of attracting oxygen and solidifying into a tar-like mass, which forms the oil paint. Perhaps, however, glycerine partially acts in the process. Ossovetsky by saturating drying oil with the salts of certain metals obtained oil colours of great durability. A mixture of very finely-divided litharge with glycerine (50 parts of litharge to 5 c.c. of anhydrous glycerine) forms a very quick (two minutes) setting cement, which is insoluble in water and oils, and is very useful in setting up chemical apparatus. The hardening is based on the reaction of the lead oxide with glycerine (Moraffsky). Lead oxide forms but few soluble salts--for instance, the nitrate and the acetate. The majority of its salts (sulphate, PbSO_{4}; carbonate, PbCO_{3}; iodide, PbI_{2}, &c.) are insoluble in water. These salts are colourless or light yellow if the acid be colourless. In lead oxide _the faculty of forming basic salts_, PbX_{2}_n_PbO or PbX_{2}_n_PbH_{2}O_{2}, is strongly developed. A similar property was observed in magnesium and also in the salts of mercury, but lead oxide forms basic salts with still greater facility, although double salts are in this case more rarely formed.[50]