Till-: RAKF. KAKTll M irPAI.S. 379 



the rare earths ami to set it ahi^ht. lie had u])ser\-e(l the intense 

 light emitted on lieating one of those oxides, and this laid the 

 foundation of the ineandeseenee mantle industry. At ])resent 

 that industry constitutes the hig-gest commercial development that 

 has yet resulted from the rare earth metals, but there are quite 

 a number of other possibilities, and Dr. J. F. Spencer, of Bedford 

 College, University of London, has recently done excellent service 

 in drawing special attention* to the rare earths, and in particular 

 to the history of their discovery, their occurrence in Nature, tlieir 

 chemical and physical properties, and their uses. In his historical 

 introduction Dr. Spencer sets forth lucidly the successive stages 

 of investigation into the nature and properties of this interesting 

 group of metals — all apparently so aimless from the viewpoint 

 of the utilitarian, and it is signiticant that from Gadolin's day 

 to our own not one decade passed without definite progress. It 

 is impossible in the space available here to attempt even an 

 outline of the many interesting facts collated by Dr. Spencer. 

 The separation of the rare earths by means of fractionation -is 

 explained in sufficient detail for a work of this character, and 

 a considerable section is devoted to the properties of the metals 

 belonging to the gr(iup and their salts, the place of the rare 

 earths in the periodic system of classifving the elements forming 

 the subject of discussion in a separate chapter. In dealing with 

 the uses of the rare earths the author rightly gives the gas mantle 

 industry first rank, but many other uses are recorded. Thorium 

 and its compounds, for example, are used for the headlights of 

 motor-cars and also for searchlights, in the production of flash- 

 light powders, for the filaments of Nernst and electric lamps, 

 and in radiology. In many organic reactions thoria acts 

 catalvticallv. aiding, iiitei' alia, in the production of ethers from 

 alcohols. Cerium earths again are used for the manufacture of 

 pyrophoric alloys, which in turn enter into the production of 

 automatic gas lighters, petrol lighters, and for indicating the 

 atmospheric paths of bullets or shells. Various other uses have 

 been found for the rare earths, but no more than bare mention 

 can be given them here : thev include the dyeing of textile 

 fabrics, the colouring of glass and porcelain, utilisation in colour 

 photography and other photographic processes, and medicinally 

 as a preventive of nausea and as a non-irritant antiseptic dress- 

 ing. An exhaustive bibliography, comprising n(T less than 1,029 

 titles, is appended. 



* T. F. Spencer: "The Metals of the Rare Earths.'V 8vo . pp. x, 279 

 diags. London: Longmans, Green and Co., tqiq. 12s. 6d net. 



