

Boll : I',Tll. 



H'l I.I Nti uK l.lgf ||,s. 



ebullition ia a/rrlnl by UK "V-"l~l nature of the lii|iii<l ilnit the law 

 according to which such ftrnn<"*l constitution u connected with the 

 boiling has been "^^ in only a comparatively few oases), and 

 tfr.1 ^ U imiintitt by iiiiimM of temperature, diminution of pressure, 

 aad diminution of adrrssVm between the boiling liquid and the ul>- 

 .unc. with which it i. in contact. 



A liquid i. .aid to be perfectly roUUle when it can be boiled away 

 without chemical change. If heat be applied to a vewl containing a 

 togU tuch rolatile liquid, iU temperature will gradually rue until it 

 nsuhes a oerUin point (dependent upon the four conditions) at which 

 boiling commence* ; that u, at which the pressure of the air i- over- 

 oomeby the expansive force of the vapour of the liquid. If the heat 

 be continually applied after thi* point is reached, the liquid U boiled 

 off in the form of vapour, but U. the hurt it retain* the same tempe- 

 rature a* that at which it commenced boiling, a temperature which 

 the vapour of the liquid ahw assumes. After the boiling has once 

 commenced the external heat U expended, not in effecting a rise of 

 temperature, but in converting the liquid into a vapour. Hence, the 

 temperature at which one and the aame volatile liquid boils U constant 

 (the other two condition* being abo constant), and that temperature is 

 called the hoilimj /W/ of the liquid under thoee conditions. 



A liquid which u boiled in an open vessel U exposed to the pressure 

 of the atmosphere, and its boiling is induced or retarded according OH 

 this pressure U less or greater. Thus, when the atmospheric pressure 

 is small [BAKOMETKR], water boils at a lower temperature and in a 

 TOMitir vessel than when it is great Hence, in determining the 

 temperature at which a liquid boils in an open vessel of fixed nature, 

 reference must be had to the existing atmospheric pressure. Con- 

 versely, from the temperature at which a simple volatile liquid l-'ils in 

 an open vessel of Axed nature, the atmospheric pressure may be 

 determined. 



It follows from the above, that if exact comparison has to be mode 

 of the temperatures at which chemically different liquids liil. the 

 determinations must be made when the liquids are subjected to the 

 same atmospheric pressure, or the effect of change of pressure on the 

 boiling point must .be ascertained, and the corresponding correction 

 made. 



In the following table are found the boiling points of various liquids 

 in contact with platinum wire, at the mean barometric pressure of 

 inches (70 millimetres). The temperatures are given on the 

 ,,. 



their corres]ionding alcohols, namely, methylic, ethylic, propylic, 

 biitylic, and amylic. Moreover the compounds resulting from the 

 union of the above acids with the radicals of the various n! 

 follow the same law. Kor not only are the boiling points of butyrato 

 of methyl, propionate of ethyl, acetate of prupyl.and formate of butyl, 

 the same (the increase of 34 "2 Kahr. due to the additional C,H, in the 

 radical being exactly counterbalanced by the removal m the 



in-ill .. but the bodies just named boil 34"".! higher ti :iate of 



methyl, acetate of ethyl, and format. which u^niii Isiil (it -2 



higher than acetate of methyl and formate of ethyl ; while these latter 

 boil 34"'2 above formate of methyl. 



In the benzol series, however, this increment of C. H, effects an 

 elevation of 43'2, while in the bromethyleue series the increase i 

 only 27. 



When an alcohol is converted into an acid by the exchange 

 equivalent* of hydrogen for two of oxygen, the boiling point i 

 thereby raised 72*. 



The above are the most perfectly developed of Kopp's lawn relating 



connection between boiling point and chemical constitution. 



Although bodies belonging to the same chemical series have boiling 



|>oinU higher or lower according to their position in that series, yet 



liquids belonging to different series may have boiling points which, 



a* far as experiment shows, perfectly coincide. 



There appears to be no relation between the specific gravit 

 liquid and its boiling point. 



The chemically combined water in a liquid seems to have great 

 influence upon its boiling point This may be connected with tin- 

 high latent heat of steam. Thus those alcohols whose boiling points 

 are below '2\2 '(ethylic) furnish, by the loss of wat-r, etln-rs whose 

 boiling points are still lower; while on alcohol which I mils above 

 . eg rue to an ether of higher boiling point than itself (amylic 

 alcohol). 



The following tables show the relation between the boiling points 'of 

 various bodies and the pressures to which they arc subjects I in 

 words they give the tension of the vapours of the bodies at different 

 temperatures. (From Buff, Zamminer, and Kopp's ' Lehrbuch der 

 physikalischeu und theorctischenCheiuie.') t denotes the temperature 

 Fahrenheit of the substance, and h the height of the column of mer- 

 cury, in inches, which the vapour will support. 



boiling points at the SUM pi assure. When two liquid., Monging to 

 the same chemical tgrp*, so differ from one another that the one 

 contains a molecule more of C,H, than the other, the boiling point of 

 the first is often it'll Kahr. above that of the second. Thus the 

 boiling points of formic, acetic, pmpionic, butyric, and valerianic acids 

 iunsiii hjr the successive increment of sr 2 Kahr., as do those of 



I. FOR WATKB. (Hcgnault.) 



t' 



26 



4 



14 



32 



50 



68 



86 



104 



t' 

 + U 



32 



50 



68 



86 

 104 

 122 

 140 

 158 

 176 

 194 

 212 



Formula- have U-en proposed to correct the pressure and the boiling 

 |Kiint, and thus to serve to derive new values by interpolation. But 

 all such formula! ore more or less empirical, and cam; .-d on 



w hen tin- value* nought are far from actually observed ones. 



t with foreign bodies, as before stated, influences the boiling 



point of a liquid to some extent. Hence in comparing the liilin K 



point* of liquids, the latter must all be in i- b tin same 



MiilMtance. generally platinum wire. When two liquids are perfectly 



mi-eil.l.-, the initial boiling point of their mixture is always above that 



li has the lowest boiling point, and during the 



iHiiling it rises (more or less suddenly, according as the re*] 



boiling points of the -separate liquids are further apart or nearer) 



until the liiK-liei lioiliiiK l>"i"t i reached, or nearly reached. But in a ' 



liquid which, t hough not mwciblc with still may be wetted by 



water, tin- presence of water depresses the Imiljng point of the 

 liquid, although the latter when dry would l,il In-low 212 

 This effect is proKibly due to the small quantity of disseminated 

 water diminishing the cohesion of the liquid. 



It is found that wh.-n two substances affect the boiling point of a 

 liquid unequally, ami both are present in it, the liquid will boil 

 temperature due to the substance which depresses its l,,.ilii, K i, ( ,jut 

 most. Hence, in practice, in determining the boiling i>oint of liquids 



