' M certain t . -mperat nre. t hat it i- accelerated hv a rise of temperature, Imt it was 



\< 'I pos-.il, ]c that eonil. ination could proceed at the ,ame temperature as that 



h decomposition ifoes on. iSertholId and Deville introduced the conception of 



eipiil hriiim int. i chemical science, and elucidated the .pi.- t;,,n of r.-versihle reactions-. 



11 V the llh Jed is yet far fr. nil heill- clear the qllest i, n is of the rate and cinnplete- 



i ' ' : reaet ion. ol contact , ,Vc.. still int rude themselv es 1ml an important step has heen 

 made in chemical mechanic-,, and it has heen made in ihi, diredimi thanks to the 

 \'- >rk uj out of many data in the sense indicated hv the dodriiies.it' I'.ert holli-i and 

 I'eville. l;,-.de, Deville h i in s,-l 1 . 1 1 1 ,- French diemi-l- Dehrav, 'I'roost, Leinome. 

 Hautdeiiille, Le ( ' 1 ia I el ier, and others have done much in w orkinj out the prohlenis 



In order t.. sh.iw the exact reseml. lance l.dweeii the pin uonieiia l evaporation ami 



' ' I ' IN he calculated ace.. I'd ill- to the lav, ol the Variation . .f d i ssoc ia t loll - 



e. ill exadlv the same manner as it is possihle to calculate the latent heat of 

 ol the econd law of the mechanical theorv ol heat. This ilepeiuleilce 



in..;, he expre ed l.v the equation: I-2IL '!'('/ ~~ |',Y,' ' wl "' lv ' '* !l "' hltl ' nt 

 heat of evaporation. PJ I the niechaiiic.il equivalent of heat. T the ahsolute temper- 

 ature ,,| transforination, T '21'.} I. i/ the weight of a cnhic measiir.' of the sul. stance 

 lidorc. and I) alter, the transformation into vapour; am' then-fore 1 ,1 \ D is the 

 - "/' n, imm proceeding in the t raiisforniiit ion, and lastlv ,1 i//i DI/I/I is the 

 ' "i the p.. . lire hv the temperature, or the vaiiation "t tension (expressed 

 in n ' ol wei III and Irn-tlii divided lv the variation of teinperat nre. In the case 

 1 lea ii. taking (he metre and k i I. >_> ra in as units, we lind. accordimj I., the data Ljiven 

 'i ' hapl.-r I., that when / llld - that i--, when T ">7:'> the chanje of volume is 

 he. ails.- one cnhic metre .>f steam at 1 MO weighs f>r,o;, kilo., whilst a ciihic 

 ; ' . ': water at I MO weighs '.ii'iO kilo. i. The magnitude of the product for steam at 

 i" 11 found from tin- I'ai 1 thai vapour lension of steam at KM) varies l.y '21 mm. of 



Hi in. rciirv column for a variation of 1 temperature. Hence the magnitude of the 

 'H "1 pre uie in kilogram per si|iiare metre ll'ii-JT I:;;.:M; :;r,",. Hence the 



iatii.li i :,:'.i; l:'l ii-J7^r,J. Thai i -. l...th part-, are e,|iial within the 

 nl il the data, and I herelme t he .piai.tit v ol heat. I .. expended in evapo 



. , , it on. \ MM i .ampl. we will cite the data ohtaiiied l.\ Tro,. I and I I a u Ldeii 1 1 le 

 ; ! . i dridi n t p..!, i nin and nd iu m. / I leiu^- the temperat lire, and A the disso- 

 ( I ioi ori me c. ,ri e |i.i"din w il h .1 in milliuiet res of I he merciirv coliinin 



in 



II. lie. ' hat III 1 lie c.l c of K II the i i ,e ol pre Ill'e pel' lie :n e at llliollt :',-Ml 



: ' mi. ol ! h,- iiiei,-iir\ column, . r l lie product '21 kil... p.-r 

 Ih, i,, , nitnde ol (he viiriul t volnmi , /. .//// I'mm the lad that the 



: . a'jonoi s,,luim i nearlv '-' 'i ". A / :;: ' (l . Mierd. >re T 1'i'j:;. and t herefore we 



mtiideo! L Iroin the equation t,, he nearlv IHIIIMI .-alone that is, jud^in^ 



ti-oiiitln variatmn o| the di ociali.Hl pre lire ol pot a mil hv d ride, t here is (lev eloped 



