WEEKS LEAD DIEYDRIDE AND LEAD TE-RZDE. 2846 CCCXCII1.-Lead Dihydride and Lead Tetrahydride. By EDWARD JOSEPH WEEKS. SOLID hydrides of arsenic (Ckm. News 1924,129 31) antimony (this vol. p. 1069) and bismuth (ibid. p. 1799) having been pre-pared the existence of a solid lead hydride was investigated. To a solution of alkali plumbit'e made from lead acetate and caustic soda or potash pure aluminium foil was added. The grey deposit obtained was washed many times with caustic potash solution and h l l y with water until the washings were neutral. It waa filtered off and dried in a vacuum desiccator over sulphuric acid for 3 4 5 days both operations being performed in an atmosphere of hydrogen. The action follows the equation 2KHPb0 + 2Al= 2KAl0 + Pb& The deposit contained lead and hydrogen only and on heating in a vacuum gave off hydrogen and left metallic lead.Details of the method of analysis have already been given for bismuth (h. cit.). 0.3253 G. gave 20 C.C. of H measured at It.7'2. and 0-3243 g. of 5 ~ 2846 GLASSTONE AND RIGGS CO-X FOEBfA!L'ION Pb. H 0.5; Pb 9901%. 0.1504 G. gave 10 C.C. of H at N.T.P. and 0.1422 g. of Pb. H 0.6 ; Pb 99.5%. On combustion 1.9550 g. gave 0.0662 g. of H,O. H 0.5% (Pb,H requires Pb 99.5; H, 0.5%). Lead dihydride heated in a tube in the absence of air gave lead and hydrogen only. No trace of PbH appeared to be formed as no lead deposit could be obtained on heating the issuing gas. The dihydride oxidises rapidly in the air and therefore must be kept in an inert gas. Fused potassium nitrate reacted vigorously with it (as with As2H2; Sb,H,; Bi2H2) but only slowly oxidised h e l y divided lead. To obtain the tetrahydride first prepared by Paneth the dihydride was heated in a silica tube in an atmosphere of pure hydrogen and the issuing gas was passed through a heated tube ; a deposit of lead was then obtained. With hydrogen alone no deposit was formed and hence it is concluded that the reduction of Pb,H follows the equation Pb2H + 3H2 = 2PbH,. BA~ERSEA GEAMMAB ScHooL, LONDON S.W. 11. [Received November 2nd 1925.