696 



STAVANGER 



STEAM 



and i it leu occurs at twinned cruciform crystals in 

 certain slates and schists. It ia reddish, yellow i-h 

 brown, or brownish black. 



StavailKer. the nm-i important town in the 

 Miuth-west of Norway, stands on the southern side 

 of Bnkken Fjortl, 1(K) miles S. of Bergen. It has 

 two harbours, entered annually by aliout 490 

 vessels of 180,000 tons bunion, and derives ita im- 

 portance from iU connection with the fisheries of 

 the adjacent coast. The town dates back to the 9th 

 century at least, but has been frequently destroyed 

 by tire, and is now quite a modern place. The 

 cathedral, a Gothic structure, was founded by an 

 English bishop (Keinald) in the llth century, but 

 was restored in 1806. Of late years it has become 

 a favourite rendezvous of tourists to Norway, 3500 

 stopping here in 1890. Pop. ( 1891 ) 23,930. 



Stavesacre (Delphinium stuphisnyriu), a 

 species of Larkspur (o.v.), a native of the south of 

 Europe. The seeds nave been used in medicine 

 from ancient times; they contain the alkaloids 

 delphinine, delphinoidine, and delphisine, and a 

 considerable quantity of a fixed nil. The seeds are 

 poisonous, causing great depression of the nervous 

 and circulatory systems, with vomiting and purg- 

 ing. They are officinal in the British pharma- 

 copeia, and from them an ointment is made which 

 is used to kill lice, this being its sole therapeutical 

 application at the present time. 



Stavropol, a town laid out in 1776 on the 

 northern slopes of the Caucasus and on the prin- 

 cipal highway between Russia and Persia. It has 

 broad streets and good stone houses, is the seat of 

 a Greek-Catholic bishop, has railway connections 

 with Rostoff near the mouth of the Don, and is a 

 rapidly growing place, with active industries and 

 a brisk trade in cattle, corn, tallow, hides. Pop. 

 36,561. The government of Stavropol has an area 

 of 26,492 sq. in. and a \rn\i. of 657,554. 



Stays. See TIGHT LACINQ. 



Stealing. See THEFT. 



Steam. Steam is the vapour of water. When 

 dry it is invisible and transparent like air, and not 

 to be confused with the semi-liquid cloud which 

 comes from the chimney of a locomotive. When 

 superheated (see below) it changes the character- 

 isi ics of a vapour for those belonging to what is 

 known as a ' perfect gas' (see GAS). The develop- 

 ment of steam is naturally enough connected 

 popularly with a high temperature, but the two 

 tiling- do not necessarily go together. Water (or 

 snow, or ice) gives off vapour or steam at every 

 temperature a low temperature not preventing 

 the formation of steam, but only decreasing its 

 density. The only limit to this evaporation in 

 when the air surrounding the water (or snow, &c.) 

 is already saturated with vapour of the maximum 

 density which the water can give off at the existing 

 temperature. Thus, water at 32 F. will give olf 

 vapour of a pressure equal to 0-085 Ib. per square 

 inch ; but if the air above it is already saturated 

 with vapour of that density the tendency of the 

 particles of water to fly apart is exactly balanced 

 by the pressure of the vapour on its surface, and 

 no more eva|>orati<m takes place. While no atmo- 

 spheric pressure can prevent the water or ice passing 

 into vapour, the previous presence in llie nir of 

 vapour of the required density (even when so small 

 as in the instance just given) entirely stops it. 



Suppose a to be a cylinder, and ji/> a piston 

 moving steam-tight within it ; anil suppose also 

 that the end of the cylinder above // is open to the 

 atmosphere, and that below p there is in the 

 cylinder a perfect vacuum. There is then a down- 

 ward pressure upon the piston equal to the whole 

 force of the atmosphere, or about 14'7 Ib. per 



square inch. If now a little water could be in- 

 troduced into the bottom of the cylinder without 

 admitting anv air, a quantity of 

 vapour would rise from it, and 

 press with more or less force on 

 the lower (tide of the piston so 

 as to sustain a portion of the 

 weight of the atmosphere. How 

 much vapour would rise, and how 

 much elastic force or pressure it 

 would exert, would depend upon 

 the temperature of the water and 

 cylinder. 



At 32 F., as we have already said, the vapour in 

 the space a would exert a pressure equal only to 

 0-085 Ib. per square inch. If the temperature were 

 raised to 80 more vaimur would rise until its 

 pressure liecame about n-;. Ib. per square inch ; at 

 102 the pressure would be 1 Ib. ; at 162, 5 Ib. ; at 

 193, 10 Ib. ; and so on, until at 212 F. the pres- 

 sure would lie 14'7 Ib., or exactly equal to that of 

 the atmosphere. When this point has been reached 

 it is evident that the piston will lie in equilibria, 

 the pressure beneath it being exactly equal to that 

 above. At each intermediate point the downward 

 pressure on //< is equal to the pressure of the 

 atmosphere minus the pressure of tne steam below 

 the piston. So far as the piston is concerned the 

 conditions are therefore the same as if the vacuum 

 had been impaired by the introduction of a certain 

 quantity of nir below j>p ; but there is this differ- 

 ence between the two cases if the space a had 

 been occupied by rarefied air, then, by forcing the 

 piston down and compressing it into less space, its 

 density would increase until its pressure liecame 

 equal to or greater than that of the external air. 

 \\ ith steam, nowever, if the piston were depressed, 

 and if the temperature of the steam were preserved 

 the same, instead of its pressure being increased, a 

 portion of it would be liquefied, ami tne remainder 

 would have the same pressure as before. 



It is at 212 F. that water in an open Teasel 

 begins to boil i.e. the vapour rises rapidly and in 

 volumes, being able to displace the atmosphere (see 

 BOILING). In this state it is usually called steam ; 

 but there is no essential difference between steam 

 at 212 and steam at 60. The steam rising from 

 boiling water in an open vessel is of the same tem- 

 perature as the water viz. 212; but, notwith- 

 standing this, it contains a great deal more heat. 

 This heat is employed in ( to use popular language) 

 forcing asunder the molecules of the steam, and 

 thus causing it to occupy so much greater a bulk 

 as steam than as water. It does not make itself 

 known by the thermometer (for which reason it is 

 called latent heat), but its existence and amount 

 are known by other means (see HEAT). In 

 speaking of the pressure of steam we have given 

 it in pounds per square inch above a perfect vacuum, 

 or as what is called an absolute pressure. This 

 must )>e carefully distinguished from pressures (as 

 often given) in pounds aiot'c atmuitphfrir presmre, 

 According to the met hod we adopt, which is the 

 more scientific one, steam of 14'7 Ib., or one atmo- 

 sphere, exactly lialances the pressure of the air, 

 and can therefore do no work against it ; while, if 

 the other nomenclature hail been adopted, steam of 

 147 Ib. above atmospheric pressure would have 

 been really steam of two atmospheres pressure. 



When a cubic inch of water is converted into 

 steam at the ordinary pressure of the atmosphere 

 it* volume is increased to 1645 cubic inches i.e. 

 a cubic inch of water becomes nearly a cubic foot 

 of steam of one atmosphere. If the steam is pro- 

 duced at any greater pressure, it* volume wilt lie 

 very nearly inversely as that pressure ; at two 

 atmospheres it would occupy about 855 cubic 

 inches ; at four atmospheres, about 457 cubic inches. 



