177 



OSJIANOSMIC ACID. 



OSMOSE. 



178 



commonly represented on rolls of papyrus as sitting in judgment on 

 departed spirits. His usual attributes are the high cap, the flail or 

 whip, and the crosier ; and he is clothed in white. Sometimes he is 

 figured with a hawk's head. He is also frequently represented with an 

 artificial beard. His titles are very numerous : Wilkinson notices 

 some of the principal (iv. 320). By the Greeks he was identified with 

 Dionysus. But Diodorus says that some have supposed him to be 

 Pluto, Pan, and even Zeus. The mysteries of Osiris, with which 

 were conjoined those of Isis, were practised with great secrecy and 

 solemnity. It was from them that the Eleusiniau mysteries were 

 derived. (Diodorus, i. 29 ; Herodotus, ii.) The chief seats of his 

 worship were Phila; and Abydos ; at the former of which the great 

 mysteries were celebrated. 



OSMASOSMIC ACID. [OSMIUM.] 



OSMIC ACID. [OSMIUM.] 



OSMIUM (Os). From oaw, odour, in allusion to the smell of 

 osraic acid. This metal was discovered by Mr. Smithson Tennant in 

 the year 1803, in the grains of native platinum [PLATINUM], along 

 with another metal [!RIDIUM]. This compound, called osmitie of 

 ;i, occurs hi flat grains and hexagonal crystals. The primary 

 form is a rhomboid. Cleavage, perpendicular to the axis. Hardness 

 4'5 to 5'1 , exceeding that of native platinum. Colour iron-gray and 

 pale steel-gray. Lustre metallic. Opaque. Specific gravity 19'5. 

 Insoluble even in aqua regia ; becomes black when fused with nitre, 

 and when heated in a tube exhales a peculiar odour. 



Berzelius analysed three varieties of osmide of iridium, from 

 Siberia, with the annexed results. 



Osmium . 

 Iridinm 



Rhodium 

 Iri.n . 



80 

 20 



100 



74-9 

 25-1 



100-0 



49-34 



46-77 



3 15 



0-74 



trace. 



100-00 



The preparation and properties of osmium have lately been studied 

 by MM. Deville and Debray. These chemists have obtained it in the 

 pulverulent, crystallised, and compact forms, by the following pro- 

 cesses. Osmide of iridium powdered, if necessary, by roasting with 

 zinc, is mixed with five and a half times its weight of binoxide of 

 barium and heated in a well covered crucible to the temperature of 

 melting silver, for two hours. The resulting black mass is then broken 

 up, distilled in a retort with eight parts of hydrochloric acid and one of 

 nitric acid, the well cooled distillate redistilled, and the vapours con- 

 densed in dilute ammonia. The osmiate of ammonia solution thus 

 formed is then saturated with sulphuretted hydrogen and boiled, and 

 the sulphide of osmium reduced by heating for four or five hours, 

 in a carbon crucible, to the temperature of melted nickel or melted 



Osmium thus obtained is pulverulent, but exhibits the metallic 

 lustre with considerable brilliancy ; has a blue colour brighter than 

 that of zinc; a specific gravity of 21 '3 or 21 '4, and, at a temperature 

 higher than that of melted zinc, a combustible. Heated to bright 

 redness, with eight times its weight of tin, in a carbon crucible, 

 and the melted mass allowed to cool slowly, it separates out in a 

 'line form, and is isolated on dissolving out the tin with hydro- 

 chloric acid. Heated by the oxyhydrogen blowpipe, in a furnace made 

 of lime, it does not fuse, but aggregates into a more or less compact 

 mass, and at the heat of melted iridium is slowly dissipated in vapour. 



Osmium combines with mercury ; the amalgam is decomposed by 

 heat, the mercury volatilising, and the osmium remaining behind in such 

 a fine state of division as to take fire on coming into contact with air; 

 in tliis condition also it is soluble in nitric acid, but is not so after 

 ignition. In classifying the elements, osmium is usually placed next to 

 arsenic; its equivalent is 99'41. 



/ and wm.iv.rn combine in five proportions, forming : 



Protoxide of Orminm . 

 Setqnioxlde of Osmium 

 Binoxide of Osmium . 

 Teroxide of Osmium 

 Osraic acid 



OlO 



O^O, 



OsO, 



OlO, 



I. o 



1. Protoxide of osmium (OsO).- - When potash is added to a solution 

 of chloride of osmium, the protoxide is precipitated in the state of 

 hydrate (OsO, HO), and is of so dark a green colour as to appear 

 nearly black. This hydrate dissolves slowly in acids, forming dark 

 green coloured solutions, which do not yield crystals by evaporation, 

 but leave green or greenish-brown translucent residues. When the 

 hydrate is heated rather below redness, it loses water. It detonates 

 when heated with certain combustible bodies. 



2. Sesr/uioxide of utm.iu.rn. (Os,0.,) has not been procured in a sepa- 

 rate state, but is obtained in combination with ammonia when the 

 binoxide is heated with excess of that alkali; nitrogen is evolved 

 during the operation by the decomposition of a portion of the binoxide 

 and of the ammonia. 



3. Biauj-ide of osmium (OsO,) is formed and precipitated by pouring 

 a solution of carbonate of soda into a saturated solution of bichloride 

 of osmium and potassium. The precipitation takes place gradually, 



ABT3 AND SCI. DIV. VOL. VI. 



and after separating, by means of hydrochloric acid, a little soda which 

 it retains, it is obtained in a state of purity ; it is of a black colour and 

 insoluble in acids. 



4. Tci-tmde of osmium (Os0 3 ), osmious acid, is prepared from the 

 terchloride in the same way as the binoxide from the bichloride. Its 

 existence, however, is not perfectly established. A crystalline com- 

 pound with potash (K0,0s0 3 , 2HO) appears to exist. 



5. Peroxide of osmium, or osmic acid (OsOJ. This is a very curious 

 compound, differing remarkably from all the preceding substances. It 

 is obtained whenever osmium is burnt in the air or in oxygen gas, or 

 when the pulverulent metal is heated with hot nitric acid. It is 

 white, very volatile, extremely fusible, soluble iu water, and crystallises 

 in colourless transparent flexible needles. It possesses an extremely 

 disagreeable odour, somewhat resembling that of chlorine. It com- 

 bines with alkalies, forming compounds which are called osmtates. 

 When sulphurous acid is added to a solution of osmic acid, it is 

 rendered yellow, orange, brown, green, and blue, dependent upon the 

 extent to which the deoxidisement is carried on. It stains the skin, is 

 acid and poisonous. 



Osmium and sulphur form four sulphides. They are produced on 

 passing sulphuretted hydrogen through the hydrochloric solutions of 

 the oxides. They much resemble the latter in constitution. 



Osmium and chlorine form four chlorides, namely, protocliloride of 

 osmium (OsCl), which sublimes in green needles on passing chlorine 

 over osmium heated in a long tube; sesquichloride of osmium (Os.,Cl 3 ), 

 known only in combination with chloride of ammonium ; bichloride of 

 osmium (OsClj), formed by excess of chlorine in the preparation of the 

 protochloride, but crystallising farther from the source of heat, and is 

 red instead of green ; and terchloride of osmium (OsCl 3 ), also known 

 only in combination with chloride of ammonium. 



Osmium and nitrogen form osmiamic acid (Os.,N0 5 ), according to 

 Gerhardt, or osmanosmic acid (OsN, OsO,), according to Fritzsche and 

 Struve. It separates as a yellow crystalline powder on adding caustic 

 'ammonia to a solution of osmic acid in potash. 



The remaining compounds of osmium have not been satisfactorily 

 studied. They are all characterised by giving fumes of osmic acid, 

 when heated with carbonate of soda on platinum foil in the blowpipe 

 flame, and the fumes are recognised by their odour. Osmic acid also 

 imparts luminosity to the flame of alcohol. 



OSMOSE. The phenomena of liquid diffusion [DIFFUSION] become 

 more complicated when the two liquids are separated by means of a 

 porous diaphragm, because in such case there is adhesion between the 

 liquids and the material of the diaphragm : nevertheless the liquids 

 will mingle together in opposition to gravity. For example, if a 

 funnel, furnished with a long narrow stem, and a piece of moistened 

 bladder tied over its mouth, be filled with spirit of wine or with 

 syrup, and be placed in a shallow vessel of water, the liquid will in 

 a few hours rise in the tube, and even overflow. In this case there 

 is a greater adhesion between water and the membrane than between 

 spirit and the membrane ; hence the water in contact with the lower 

 surface of the membrane rises into it by capillary attraction, and gains 

 the upper surface where diffusion of the water through the spirit sets 

 in, and is promoted by the adhesion existing between the two liquids. 

 In this way the liquid within the funnel increases in bulk, and fills and 

 even overflows the tube. This flowing in of the liquid was termed by 

 Dutrochet endosmosis, from tvtov " inwards," and a<r/j.ot " impulse." 

 While this force is acting from without inwards, a small quantity of 

 spirit is passing out into the water below, which process of flowing 

 out is termed exotmosis. If two other liquids be selected the pheno- 

 mena will be produced, provided one liquid adhere to the bladder more 

 perfectly than the other, and the two liquids have a certain degree of 

 adhesion for each other. 



Graham (' Phil. Trans.,' 1854) has investigated the subject, which is 

 one of great interest, physiologically as well as chemically. The 

 instrument used in his experiments is termed an lumomcter : it is 

 formed of a bell-glass of five or six ounces, having a plate of perforated 

 zinc over its open mouth, and outside this is securely tied a piece of 

 fresh ox-bladder with the muscular coat removed ; or else an artificial 

 membrane of calico soaked in white of egg, and dipped in boiling 

 water to coagulate it. A tube ^th of the diameter of the mouth of 

 the bell-glass, is fitted into an aperture at its top, and is graduated 

 into millimetres, each degree being about th of an inch. A rise or 

 fall in the liquid in the tube, amounting to 100 millimetres, represents 

 the entrance or removal of a stratum of liquid 1 millimetre thick over 

 the surface of the membrane. The saline solution to be examined is 

 placed in the jar, until it stands at a fixed mark iu the tube. The 

 jar is then placed on a tripod within a tall cylinder, into which 

 distilled water is poured up to the level of the liquid in the tube, and 

 this level is maintained during the experiment by adding or removing 

 water from the outer jar. In this way it was found 1. That neutral 

 organic substances, such as urea, gum arabic, sugar of milk, gelatine, 

 and salicin, exert little or no osmotic action. 2. That strictly neutral 

 salts, such as sulphate of magnesia, chloride of sodium, and chloride 

 of barium, have no peculiar osmotic action, but follow nearly the 

 same rate of diffusion as when no diaphragm is used. 3. That alkaline 

 solutions, especially those of potash and soda, produce energetic 

 osmotic results : dilute solutions containing not more than 2 per cent. 

 of the salt, answered best ; but the efl'ect was observed wheu 1 part of 



a 



