V o t . XVI.
OCTOBER,1894.
No.
IO.
THE JOURNAL OF THE
AMERICAN CHEMICAL SOCIETY. CONTRIBUTIONS TO T H E CHEMISTRY OF CER1Un.I BY I,. M.
T
DENNIS AND
W. H. MAGEE.
HE mineral cerite was first found in one of the iron mines
of Basttias, in Westmanland, Sweden. Its peculiarity was noticed as early as 1751 by Cronstedt,* and in 1784 it was analyzed by d ’ E l h ~ y a rin , ~Bergmann’s laboratbry, and was considered by these two chemists to be a silicate of lime and iron. In I 803 the mineral was again examined by Berzelius and Hisinger, and by Klaproth, and nearly at the same time, but independently, they discovered in the mineral a new oxide. Berzelius and Hisinger named the earth ceria,‘ after the planet Ceres which had been discovered two years befqre by Piazzi. Klaproth called it ochroiterde,’ from its brownish-yellow color, Fortunately th’e former name was adopted, for the latter name would have been a misnomer, since pure cerium dioxide, as we now know it, has a pale-yellow color. From that time to the present, cerium and its compounds have frequently been the subject of investigation, but the work of the earlier chemists is not of direct importance, since the ceria upon which they worked was, as we now know, a mixture of various oxides, chief among them being those of cerium, lanthanum, and didymium. In 1839,however, Mosander make known a discovery of the highest importance; namely, that ceria was not a simple oxide 1 Read at the Brooklyn Meeting, August rg,r@. ~ S UVel. . Akad. Handl., ~ 7 5 1S. , 227. SSu. Vet. Akad. Handl., 2784, S. 121. 4Afhandl. i. Fysik, Kemioch Minprul.. I, 58. 5 A , Cehl., a, 303 ; Beitrege. A , 140.
650
.I
11. D E N N I S A N D W . 13. M-kGEE.
but a mixture of at least two. T h e newly isolated earth he called lanflzana, and this, in 1842, he split up into laritliaiia .' proper, and another oxide which he named dilZj,iiiI'~(. Dating from the time of Mosaiider's discoveries. the results of the various investigations upon ceriuiii acquire, of course, niucli greater value, but the chemistry of this cleiiieiit ant1 the other rare earths has remained one of tlie most difficult probleiiis iii the field of inorganic cheinistry, chiefly because of the great similarity i n tlie clieniical Ijeliavior of these different eleiiiei1ts and the consequent difficulty of separating any oiie oi theiii completely froin the others. Saturally. then, i n a n experiiiieiital investigation of the conipounds of ceriuiii, tlic first probleiii to be solved is the preparation of pure ceria. I , SEPAKATIOS OF C E R I . ~ F R O N 'rI-Iz O T H E R EARTI-IS. T h e ceria was extracted from allanite from Xiiielia County, T'irginia, a large amount of this mineral having beeii most kindly sent to us b5' Professor IV,G . Brown, of the Washington and Lee University. Xitieteen hundred and twenty-four granis of the finely powdered allaiiite was heated in large porcelain evaporators xith concentrated hydrochloric acid until the supernatant liquid became dark brown. T h e syrupy liquid was allowed to cool and was then poured off, the residual mineral being again treated i n the same niaiiner until it became grayish-white. three treatments of about ten hours each usually sufficing. -1 portion of tlie residue was then nioistened with concentrated sulphuric acid and heated until all of the acid was driven off. T h e white residue was thrown, in small portions at a time, into ice-water, and to the filtered solution, oxalic acid v a s added. S o precipitate resulted showing that the treatment with hydrochloric acid had removed all of the rare earths. T h e rare earth chlorides, mixed with those of iron, aluniinum, calcium, etc., were then diluted and filtered. -1portion of this filtrate was treated with hydrogen sulphide for twentyfour hours, the solution being kept at 7oo, but ti0 precipitate appeared. T h e hydrogen sulphide was then expelled by boiling, the sulphur was filtered off, and the filtrate was added to /,
1 I.br/i. Skund. iYatutjf. S~ockholna,IYJ~, j5;: f v u k t . Chem.. 30, 276.
J%iI. Mag., 28, 241 ;
1'u.s.r. A u p ? . , 56, 503 ;
CONTRIBUTIONS TO THE CHEMISTRY OF CERIUM.
651
the original solution. T h i s was oxidized by nitric acid and a concentrated solution of oxalic acid was then added in excess. T h e pinkish-white precipitate of the rare earth oxalates was allowed to settle, and the oxalates were then washed by decantation with hot water until the supernatant liquid was colorless. They were then digested in large evaporators with one per cent. hydrochloric acid until all iron had been removed and were then dried and ignited in a muffle furnace. T h e reddish-brown oxides resulting weighed 410 grams, a yield of over twenty-one per cent. T h e oxides were dissolved in concentrated nitric acid. To facilitate solution sulphurous acid was added to one portion and oxalic acid to another, but with no perceptible benefit in either case. There were obtained four liters of an almost syrupy solution which showed the didymium absorption bands very strongly. Many different methods for separating the ceria from the accompanying earths have been proposed but none of them seem to yield cerium which is completely free from lanthanum and didymium unless the method proposed be many times repeated. Mosander,' the earliest worker upon this problem, obtained a mixture of didyniia and lanthana free from ceria by precipitating the mixed chlorides with potassium or sodium hydroxide and passing chlorine through the suspended hydroxides. Cerous hydroxide is oxidized to the insoluble ceric hydroxide while the hydroxides of lanthanum and didymium are changed to chlorides and dissolve. Jolin' found that the treatment niust be made seven times before the ceria is completely free from didyniia and lanthana. Popp3 added sodium acetate to the solution of the chlorides and ran in chlorine, the cerium being precipitated. Later instead of passing in chlorine gas he added sodium hy-pochlorite and boiled. Gibbs' boiled the niixed earths with nitric acid ( I : 2 ) having first added considerable lead dioxide. Zschiesche' heated the rare earth sulphates with red lead and nitric acid. I n each of the last two methods ceric oxide is formed. Winkler' separated ceria and didymia from lanthana by adding 1 Phil.Mag., 18, 241. 2 Bihang till K.Su. Vel. Aka$. Handl., 8 A n n . , 131,359;J. B., rS64, 195 and 702.
4SaIl. A m e r J o u r . , [2] 37. 332, 6 J . p r a k t . Chem., r q , 65. 6 J . p r a l : . Chem., 95,410.
a , 14;Bull. Sot. Chim., [2] a i , 533.
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