URANUS. 



URANUS. 



498 



diluted ; but dissolves in the latter, when concentrated : nitric acid 

 also dissolves it, but nitrate of peroxide of uranium is obtained. 



This oxide may likewise be obtained in the moist way, and then it 

 is soluble in dilute acids : it is precipitated in the state of hydrate, by 

 adding ammonia to the green solution of chloride of uranium ; the 

 precipitate is of a reddish-brown colour, which by ebullition becomes 

 black and dense, probably because it is dehydrated. It may also be 

 procured by putting fragments of marble into the green solution of 

 chloride of uranium. 



Black Oxide of Uranium (2UO, U 2 S ) is obtained by calcining the 

 nitrate at a high temperature. It is not decomposable by heat ; when 

 added to acids they do not directly combine with it, but a mixture of 

 salts of the protoxide and peroxide is formed. 



Olive Oxule of Uranium (UO, U.,0.,). When any of the preceding 

 oxides are submitted at a low red heat to the action of oxygen, the 

 olive-coloured oxide is formed. It has a velvety appearance, and 

 when strongly heated it loses oxygen and is converted into the black 

 oxide, and when acted upon by acids there is formed a mixture of 

 yellow and green salts, in which the salts of the peroxide exist in the 

 larger proportion, and this is an advantageous process for preparing 

 them. 



Peroxide of Uranium, or Oxide of the Yellow Sails (U.,0,). This 

 oxide, which is of all the most important, is obtained with difficulty in 

 a separate state : when nitrate of uranium is decomposed with a 

 gentle heat, an orange-coloured subsalt remains, which by the applica- 

 tion of a stronger heat becomes olive and then black oxide ; when an 

 alkali is poured into a saline solution of this oxide, the yellow pre- 

 cipitate formed retains alkali in combination ; even uranate of ammonia 

 resists the prolonged action of boiling water and also of a vacuum ; by 

 heat the ammonia and water are not expelled till peroxide itself under- 

 goes decomposition. 



Chlorine and Cranium. The protochloride (UC1) is obtained by 

 passing a current of dry chlorine gas over an intimate mixture of equal 

 parts of any oxide of uranium and charcoal submitted in a glass tube 

 to a high temperature. The chloride of uranium formed appears in 

 the state of a red vapour, and condenses in the cool part of the tube in 

 very regular octahedrons of a metallic lustre, and of a black or green 

 colour according to their size. 



Chloride of uranium is volatile, and attracts water so strongly that 

 it very soon becomes fluid by exposure to the air, the moisture of 

 which also decomposes it. 



fi'/ti-hloride of Uranium (U,Clj). This compound is obtained by 

 passing a current of dry hydrogen gas over the chloride of uranium 

 moderately heated in a glass tube. The residue of this operation is of 

 a deep brown colour, in fine filaments which are but slightly volatile 

 at the temperature at which it is formed : it is very soluble in water ; 

 the solution is purple at first, but in a few seconds it becomes green ; 

 it gives out hydrogen gas, and at the same time deposits a red powder, 

 which is very probably oxide of uranium, yielded in consequence of the 

 transformation of this substance into chloride of uranium. 



hide of Cranium of a black colour may be obtained by adding 

 the alkaline sulphides to solutions of uranium, or by passing the 

 vapour of sulphide of carbon over the oxide at a high temperature. 



We shall now briefly notice some of the oxyralts of uranium. 



Imte afPrgtoxide <>f Uranium. This salt is obtained by adding 

 sulphuric acid to the protochloride of uranium, and heating the mix- 

 ture, by which hydrochloric acid is expelled, and sulphate of uranium 

 remains; by dissolving the residue in water, and evaporating the 

 solution, green prismatic crystals of the sulphate are formed. 



It frequently happens that the crystals possess a silky lustre, are 

 greenish, and but slightly soluble in water ; in this case they contain 

 excess of base. This salt yielded by analysis : 



Sulphuric acid 28-0 



Protoxide of uranium 46'1 



Water JS-9 



100- 



Oxalatc of Protoxide of Uranium. This salt is of a greenish-white 

 colour, and very slightly soluble in water either cold or hot. It may 

 be prepared by mixing solutions of oxalic acid and chloride of ura- 

 nium ; the precipitate formed is to be repeatedly washed with boiling 

 water, in order to dissolve the yellow oxalate of the peroxide, which is 

 more soluble, and which is first precipitated. The protoxalate of 

 uranium , after being dried, may be exposed to the air without under- 

 going any perceptible change. 



'ate of Peroxide of Uranium (U,0 3 ,N0 5 + 6Aq.). This salt is 

 easily obtained in fine regular crystals. It is of a yellowish colour, 

 effloresces in vacuo, and loses half its water of crystallisation. 



Uranium forms a considerable number of double salts, which wo 

 have not thought it requisite to describe. 



Peroxide of uranium is employed in colouring glass, to which it 

 imparts a fine lemon yellow. 



URANUS, the next planet beyond Saturn, counting outwards from 

 the sun. This important member of the planetary system was dis- 

 covered by Sir William Herechel in the year 1781. On the evening of 

 the I3th of March of that year, while examining certain small stars in 

 the constellation Gemini, the attention of the astronomer was, drawn to 



AXIS A>D SCI. DIV. VOL. VIII. 



a small star which appeared sensibly larger than those in its vicinity. 

 With the view of testing the object he applied different magnifying 

 powers to his telescope, whereupon he found that the apparent magni- 

 tude of the star in question varied in the direct ratio of the magnifying 

 power, while the stars around it when similarly surveyed by him 

 exhibited only a slightly perceptible change of apparent diameter. 

 Suspecting from this circumstance that the object was a comet, lie 

 proceeded to make careful observations of its position by measuring its 

 distance from the stars near to it. A few nights only elapsed before 

 he obtained undoubted evidence of the star being in a state of motion. 

 It appeared to be travelling slowly in the order of the signs, in an orbit 

 inclined at a small angle to the plane of the ecliptic. Having con- 

 tinued his observations down to the 19th of April, he then drew up an 

 account of them, and communicated it to the Royal Society in a paper 

 which was read before that body on the 26th of the same month. He 

 appears to have been under the impression that the object discovered 

 by him was no other than a comet. 



Attempts were made by various astronomers on the Continent to 

 determine the orbit of the supposed comet, on the hypothesis of its 

 revolving in a parabola with a comparatively small perihelion distance ; 

 but it was found impossible to represent the observed motion of the 

 body in this manner, except for a very small arc of the orbit. At length 

 Lexell, in a paper which he communicated to the Academy of Sciences 

 of St. Petersburg, announced certain fa'jts, which seemed to indicate 

 that the object discovered by Herschel was in reality a planet. In the 

 first place, it differed from a comet in being well defined. On the other 

 hand, it did not exhibit the bright piercing light of the fixed stars, 

 But while thus unlike a comet or a star, it exhibited several features 

 which tended to support the idea of its being a planet. It was to be 

 remarked that, like all the planets, it travelled in the celestial sphere ill 

 the order of the signs. Again, while it was actually situate near the 

 ecliptic, its motion in latitude was exceedingly small, a circumstance 

 which seemed to indicate that like the planets it revolved in an orbit, 

 confined within the limits of the zodiac. But Lexell obtained still more 

 convincing evidence in support of his suspicion that the object was a 

 planet. Taking two extreme observations of its position, one of them 

 by Herschel, dated March 17, 1781, and the other by Maskelyne, dated 

 May 11, of the same year, he found that they might be well repre- 

 sented by supposing the body to revolve in a circular orbit, the radius 

 of which amounted to 18'93, the radius of the earth's orbit being 

 assumed equal to unity. Astronomers henceforward agreed in sup- 

 posing that the object discovered by Herschel was in reality a planet 

 revolving around the sun in the region beyond Saturn. It was soon 

 found, however, that a circular orbit was incapable of satisfying the 

 observations, and that the real orbit must be an ellipse of slight 

 excentricity. Laplace, in 1783, first determined the elliptic elements 

 of the planet's orbit, which he communicated to the Academy of 

 Sciences in the same year. 



The right of naming the new planet belonged to the discoverer, who 

 proposed to call it the (icoryium Sidui, as a mark of gratitude to his 

 munificent patron George III., under whose auspices he was enabled 

 to prosecute his astronomical labours. This designation, however, was 

 at variance with the nomenclature hitherto employed in the planetary 

 system, and the name of Uranus, suggested by the German astronomer, 

 Bode, is that by which it is usually designated. 



Herschel found by niicrometric measures that the apparent diameter 

 of the new planet, when viewed at its mean distance from the earth, 

 amounted to 8"-yl. This gave 34,217 miles for the value of its 

 absolute diameter. It was, therefore, after Jupiter and Saturn, by far 

 the most considerable of the planetary bodies hitherto recognised as 

 revolving around the sun. 



It appeared from an examination of the recorded observations of 

 Flamsteed and several succeeding astronomers, that Uranus had been 

 observed on several occasions, previous to its actual discovery as a 

 planet in 1781, under the impression of its being a fixed star. These 

 early positions proved exceedingly valuable in enabling astronomers 

 speedily to determine the elements of the orbit with a degree of pre- 

 cision which, from the slow motion of the planet, could otherwise have 

 been expected to result only after the lapse of a considerable number 

 of years. In 1790 Delambre obtained the prize of the Academy of 

 Sciences of Paris for the construction of tables of the planet. These 

 tables were founded on the observations made subsequently to the 

 discovery of the planet in 1781, and on certain earlier determinations 

 of its position. For several years they sufficed to represent the 

 observed motion of the planet with tolerable precision, but eventually 

 discordances became apparent, which continued to increase in magni- 

 tude from year to year. In 1821 Bouvard published new tables of the 

 planet. They were based exclusively on the observations made after 

 the discovery of the planet by Herschel, their author having found it 

 impossible to satisfy by means of the same orbit both the earlier and 

 the more modern observations. These tables continued for a few years 

 to represent the motion of the planet with all desirable precision ; but 

 they, in their turn, soon began to deviate from the results of observa- 

 tion, and the discordances continued steadily to increase in magnitude. 

 The reader is aware that the study of these irregularities led to the 

 discovery of a new planet beyond Uranus. In a preceding article 

 [NEPTUNE] a detailed account has been given of the circumstances 

 connected with tlu-j memorable triumph of science. 



