OSMOSE 



OSPREY 



653 



substance known, its specific gravity being 22'477. 

 Four oxides of osmium are known. Three of 

 these viz. the protoxide, OsO, the sesquioxide 

 Os.,0,, and the binoxide, OsO,, are black or 

 grayish-black powders. The peroxide, OsO 4 , com- 

 monly called osmic acid, is the most important 

 oxide. It is produced when the metal is heated 

 strongly in air or oxygen, and forms colourless, 

 glistening, acictilar crystals, freely soluble in 

 water, and very volatile. At about 100 C. this 

 compound gives off an extremely irritating and 

 irrespirable vapour; and hence the name of the 

 metal (from the Greek word osme, 'odour'). It 

 produces a permanent black stain upon the skin, 

 and at the same time causes an eruption which 

 is difficult to heal. It violently attacks all the 

 mucous membranes, and its vapour may cause 

 partial or total blindness by depositing a" film of 

 metallic osmium on the eyes. A solution of the 

 peroxide is employed in histological work for stain- 

 ing fat and nerve substance. Osmium also forms 

 two chlorides; and osmates, corresponding to an 

 imknown osmic acid, have been prepared. This 

 metal was discovered by Tennant in 1803. 



Osmose, the interdiffusion of two liquids 

 through a septum, usually of bladder or of parch- 

 ment paper. If a liottle, filled with one liquid, be 

 closed by parchment paper, and be completely im- 

 mersed in a vessel containing another liquid, increase 

 or decrease of the contents of the bottle will occur 

 according as the liquid contained in the bottle passes 

 out through the septum less quickly or more quickly 

 than the other liquid passes inwards. When the 

 contents are increased the phenomenon has been 

 called end osmose ; when they decrease it has l>een 

 termed exomnose. The distinction is obviously not 

 a scientific one ; for a reversal of the positions of 

 the liquids will cause a reversal of the osmotic 

 process, so that the process which was formerly 

 denominated exosmose must now be called endos- 

 mose, and vice versii. The phenomenon is one of 

 extreme importance, for it is constantly taking 

 place in living bodies both animal and vegetable. 

 Nollct was the first to record the occurrence of 

 osmose. He placed a vessel, filled with alcohol 

 and closed with a piece of bladder, inside a larger 

 vessel which was filled with water. The rapid 

 entry of the water almost burst the bladder ; and 

 the opposite effect took place when the water was 

 placed inside the inner vessel and the alcohol was 

 placed outside it. Nollet did not pursue his obser- 

 vations any further. Dutrochet first made careful 

 investigations into the subject, which has since re- 

 ceived numerous practical applications notably in 

 the method of dialysis, which is due to Graham. 

 The phenomenon consists merely in the inter- 

 ditfusion of two liquids complicated by the mutual 

 molecular actions which take place lietween the 

 liquids and the material of the membrane. The 

 rate of interdiffusion depends greatly upon the 

 nature of the membrane ; sometimes the direction 

 of the osmose is affected when the membrane is 

 altered. The action being essentially molecular, 

 we can readily understand how sap may be raised 

 to great heights in plants and trees against the 

 action of gravity ; for the molecular forces in a drop 

 of water (say) are sufficiently powerful to hold the 

 parts of the drop together against the gravitational 

 attraction of the whole earth. 



A pr.K-i.HS which is analogous to osmose occurs 

 in the interdiffiision of two liquids through an 

 intervening liquid layer. The difference l>etween 

 the rates of diffusion of colloids and crystalloids is 

 even more marked when the substances are separ- 

 ated by parchment paper or animal membrane 

 than when they diffuse directly into each other. 



Osnabriiek, a town in the Prussian province 

 of Hanover, in the fertile valley of the Hase 75 

 miles by rail SSVV. of Bremen and 70 WSW. of 

 Hanover. Its great Catholic cathedral, in the 

 I natibon style of the first half of the 13th century, 

 is rich in relics and monuments ; and the town-hall 



1480-1512) contains portraits of all the pleni- 

 potentiaries who here on 24th October 1648 signed 

 the ]>eace of Westphalia. By that treaty" the 

 bishopric of Osnabriiek, founded by Charlemagne 

 about 810, was to be occupied alternately by a 

 Catholic prelate and a Protestant secular prince of 

 the House of Brunswick-Liineburg. After having 

 last l.een held by Frederick, Duke of York, the 

 district of Osnabriiek came in 1802 to Hanover, and 

 the chapter was dissolved, until the re establishment 

 of the bishopric in 1857. Osnabriiek has important 

 iron and steel works, and manufactures of railway 

 plant, agricultural machinery, gas-meters, paper, 

 tobacco, &c. Dating from 778, it suffered much in 

 the Thirty Years' War, but recovered, thanks to 

 its linen industry, during the 18th century. The 

 name Osnaburgs given to coarse linens is derived 

 hence. Pop. (1852) 13,718; (1875) 29,850; (1885) 

 86,899 (of whom 12,086 were Catholics) ; (1890) 

 39,920. See works by Moser, by Frideii and Stiive 

 (1816-26 ), and by E. Miiller (1868). 



Osprey (Pandion fialiaftiis), or FISH-HAWK, a 

 not infrequent autumnal visitor to British shores, 

 estuaries, and lochs, where it feeds exclusively on 

 nsh. It has been known to breed in England, and 

 several eyries still remain in Scotland. But its 



Osprey (Pandion kaliaetus). 



Osmunda. See ROYAL FERN. 



distribution is almost cosmopolitan, for it occurs 

 on all the continents, especially where fish are 

 common and men rare. The male bird is 22 inches 

 in length, the female 24. ' The adult male has the 

 head and nape white, streaked with brown; upper 

 plumage umber, with a purplish, tinge ; under 

 parts white, with a band of brown spots across the 

 breast; cere, legs, and toes greenish blue.' The 

 female has more brown on the breast. A large 

 nest of sticks and turf, with a small moss-lined 

 cavity for the eggs, is built on a tree or rock. 

 The eggs (two or three) are laid in April or 

 Stay, and have a 'ground colour of white or buff, 

 with chestnut or claret blotches, and blurs of 

 purplish gray.' In North America the osprey is 

 gregarious. It never preys on other birds, and is 

 not dreaded by them. It is, indeed, of a pacific 

 and timorous disposition, and readily abandons 

 its prey to the White-headed Eagle. In the days 

 of falconry it was sometimes trained and used 

 for catching fish. See Howard Saundere, British 

 limls. 



