August II, 1887] 



NATURE 



357 



to their work either by hard wood packing placed i^ainst the 

 permanent structure, or by temporary girders brought into proper 

 position. In these machines the pressure employed was 3 tons 

 per square inch. A large amount of excellent work was per- 

 formed by these machines in positions where it was practically 

 impossible to do it otherwise. 



The riveting of the vertical columns of the piers is done by 

 riveting machines attached to the under sides of the lifting plat- 

 forms. They are lifted with the platforms, and do their wo k 

 while the platform is at rest. They consist of two longitudinal 

 girders or uprights, one on the outside and the other on the in- 

 side of the column. Along the face of each girder a riveting 

 cylinder is raised or lowered by hydraulic power. The inside 

 girder has a trunnion at top and bottom, fitting into a step in two 

 temporary diaphragms for supporting the thrust of the rams in 

 riveting. It is turned round on the trunnions at will, so as to 

 rivet up an entire length of 16 feet of the tube both circum- 

 ferentially and longitudinally. The outside girder and riveting 

 cylinder when at work always face the inside. The outside 

 girder is attached at top and bottom to two wrought-iron rings, 

 which encircle the column, and not only furnish the necessary 

 support but also permit of the machine being moved round the 

 column by hydraulic power as required. Over 800 rivets have 

 been closed in a day by one of these machines. 



In the erection of the large piers of the bridge, hydraulic 

 power is utilized to a great extent. The principle adopted is to 

 iniild the piers from off a platform raised by hydraulic pressure 

 as the work of erection proceeds, utilizing the piers themselves 

 in process of building as the support of the rising platform. 



THE CHEMISTRY OF THE RARE EARTHS. 



I T is now nearly twelve months since the chemical world was 

 agitated by the memorable departure made by Mr. Crookes, 

 in his address to the Chemical Section of the British Associa- 

 tion, in attempting to translate into language thoughts which had 

 ben irresistibly forced home to the minds of many men of 

 science as to the insufficiency of the theories of our modern 

 chemical philosophy to account for the presence in our midst of 

 those objects of ever-increasing interest, the chemical elements. 

 It will be remembered that, both in the address referre.l to and 

 in his lecture at the Royal Institution on the "Genesis of the 

 Elements," Mr. Crookes based a large portion of his arguments 

 upon the remarkable experiences which he himself had met with 

 in endeavouring to separate the constituents of the rare earths 

 contained in several sparsely distributed minerals. It may be of 

 interest just to recall the main conclusions drawn by the lecturer 

 from his experiments upon the substances yielded by the 

 laborious but fruitful process of fractionation. Yttrium, which 

 only two years ago was supposed to be a simple substance, fell 

 under that nil desperandum sorting influence into five com- 

 ponents, each of which presented a distinct phosphorescent 

 spectrum ; samarium, one of the constituents of old didymium, 

 was found to consist of two and possibly of three ingredients ; 

 and finally, the two components of didymium itself, into which 

 it had been separated by Dr. Auer von Welsbach, were shown 

 by Mr. Crookes, M. de Boisbaudran, and M. Demar9ay to 

 consist themselves of several. 



Contemporaneously with the work which has been carried on 

 by these and other experimenters, Drs. Kriiss and Nilson, who 

 have at their disposal tolerably large quantities of Scandinavian 

 minerals containing rare earths, have been engaged upon work 

 of a similar nature, and have lately published in the Berichte of 

 the German Chemical Society results of the highest interest, 

 not only confirming the conclusions above referred to, but an- 

 nouncing that, "in place of the rare metals erbium, holmium, 

 thulium, didymium, and samarium, we must now accept the 

 existence of more than twenty elements." 



Considering the interest which Mr. Crookes's addresses have 

 called forth, and the important bearing of this contemporaneous 

 work upon a subject of such paramount importance to the first 



nciples of chemistry, it may be of advantage to give a short 

 ription of the experiments which have led to results of such 

 .nitude. 



! lie minerals examined were specimens of thorite from Brevig 

 ...J Arendal, in the province of Christiansand, of wohlerite 

 from Brevig, cerite from Bastnas, fergusonite from Arendal and 

 Vtterby, and of euxenite from Ilittero and Arendal, The 



nitrates of the earths contained in these minerals gave very 

 beautiful absorption-spectra, and a precise measurement of the 

 positions of the lines and bands in these spectra resulted in the 

 surprising observation that in certain minerals only a particular 

 few of the absorption-bands of the nitrates of some of the rare 

 earths were visible ; thus, only one line out of all the lines con- 

 sidered to belong to the nitrate of holmium, the metal which 

 Soret called X, was visible in any intensity in the spectrum of 

 the nitrates from thorite of Brevig ; moreover, this particular 

 line is but insignificant, among many much more intense, in the 

 usual spectrum of the nitrate of holmium. The more intense 

 lines were either not at all or only faintly visible in the spectrum 

 of thorite of Brevig ; hence it is concluded that Soret's X 

 must consist of at least two ingredients, of which one is found 

 free in thorite of Brevig, and gives this one line of wave-length 

 4287- 



In these observations a single 60° prism of dispersion 

 A - Ho = 4° i8' was preferred, inasmuch as weak lines or bands 

 cannot be distinctly seen with more dispersion, and the position 

 of maximum darkness becomes more difficult to fix ; the spectro- 

 scope was fitted with the most refined micrometer arrangement 

 for the accurate determination of the wave-lengths, so that the 

 whole of the work may be checked by future observers. Before 

 passing to the discussion of the main results of the experiments, 

 a brief description of the procedure in case of one of the 

 minerals examined may not be without interest. Thorite of 

 Brevig is a typical specimen of the Scandinavian rare earth 

 minerals, and its treatment was as follows. After removal of 

 the thoria, which was required for the purpose of determining 

 the atomic weight of thorium, the solution in ice-cold water of 

 the sulphates of the mixed earths was precipitated by oxalic 

 acid, leaving the iron, manganese, and uranium in solution. The 

 oxalates were then ignited and the residual earths again con- 

 verted to sulphates ; the sulphates were converted to hydrates 

 by precipitation with ammonia, and the hydrates dissolved in 

 nitric acid, by which a lovely pink solution of the nitrates was 

 obtained. As small quantitities of thorium and cerium were 

 still contained in the mixture, the nitrate solution was evaporated 

 to dryness, and the residue ignited, whereby the thorium and 

 cerium nitrates were converted into insoluble basic salts. The 

 filtered solution of the residue then contained the nitrates of the 

 didymium and yttrium metals, and gave the following absorption- 

 spectrum : — 



Thorite of Brevig. 



