clrawii aiid the n-hole allon-ed to freeze. -1 s p i r d of fiiie co1)per wire vas iio\v droppe8:l iii :uid the tulie sealed 1 1 1 1 ivitli tlie bla.st Iaiiip. TYlieii tiie tulle was coiiipletel!. cooled, it \vas iii\-ertecl aiitl tlie acid allonetl to iiielt aiitl n i i i clo~vii into the eiid jiist sealed. Tlie free iodin v.liicli liatl separated at this poiiit dissol\.ed in tlie acid. 1)iit \v;i.q ciiiickl!. r e i i i o \ d h!. the copper. lea\-iiig :I perfectl!. coIor1~s.sliqiiitl, n-liicli \vas tlieii tlistilled into the l i i i i l i h 1 ) ~ siiiipl!. . siirroiiiidiiig the latter \\.it11 solicl c:irhoii diosicl. It ma!- lie iioted litmre that distillatioii alone \vi11 nliiiost coiiipletelJ- ft-ec the liqiiid froiii iodin. Finall!. wlieii the ivliole o f t h e acid 1i:~lpwsed oi.er aiid iolidifietl, a \ w y fiiie poiiited flailit- \va,s applied to the cnpillarj- (1% \vhicli instaliti!. sealed np ivitli tlie appeai-aiice of oiilj. tlie slialitest trace of frer iodiii : scucel!. eii(.iitg-li% i i i fact, to gi1.e a percepti1)le color to t h e liqiiid \vlien r l i , ~ s o l ~ iii ~ e dit. This tube \vas placeti at the hottoin of a caloriiiieter ciip cmitaiiiiiig 500 of \vatel-. Tlie tlieriiioiiietei-. ,stirrer, etc., \\-ere placed iii position and tlie n-liole allon-ed to staiirl o \ w iiiglit in a rooiii in the 1ias;ciiieiit ; tlie (1et~i.iiiiiiatioiislieiiig iiiatle tlir first thing iii the iiioi-iiiiig. T h e coiiteiits of tlie caloriiiieter cup were kcpt .stin-etl l)!. a three-hladed platiiiuiii stirrer operated h!- aii electric iiiotor. T h e teiiiperature \vx. read 11)- telescope oii a I~ecki1i:iiiii Imiliiigpoint thernioiiieter di\-idetl to O.OI C, nliicli Iiatl l ~ e i icoiiip i - e d n-itli a r;t:uiclard tlieriiioiiieter fi-om tlie \-ale ( )liser\-atoi-!.. -1c 1o c k n-o r k tapper \vas 1;e11t 1.11ii ii i i i g oii t 1i i s t h r c) I I 2-1i ii11t c w 1i deterniiiiatioii. T h e coiiteiits of tlie t i i h \vert. tliscliarx-:-etl iiitci tlie ivntei- l)!. siiippiiiy off the capillar!. tip li!. iiieaiia of ;I loop i i i tlie end of a platiiiiiiii \T.irt.. Thr liqiiitl \vas prci,ji.ctrtl into thy I into solution Lvitlioiit the lash o f :t y i i i g l i . I ~ i i l i lilt.. Tlie total tlieriiial capacitJ- of tlic caloriiiieter clip and conof \vater. teiit \ V ~ Se~11ialto T h e tlilutioii ( I iiiol of H I to o \ w 700 mol.: \vnteri \vas siifficiiriit t o 1 )c taken :is intiiiite. 'I'lie iiiitinl teiiiperntiire \v;is i i i e:icli c:we ivitliiii a fe\v teiitlis of I 2 ' . T h e f o l l o \ v i i i g is the (lata for tlii-ye tleteriiiinatioiis. T/Tvcixlit of acid taken. At rise ~
494
F. G, Cottrc ZZ
in temperature corrected for errors of thennometer and for radiation. Q = heat liberated by solution of I g-mol HI (126.89 g-1 expressed in K ( r K = heat necessary to raise 100 g water I O C at temperature of experiment).
\v
S O
-
I 2
3
~
I
3.i299 g 4.7OS6 4.6961
Q
At
~~~__________
0.S60” I .OS0 I
1.085
1
Mean
I.FS.3 E: 14s 0 143.7
-_
148.3
T h e value for the solution of the gaseous acid is given by Thonisenl as 192.1 K ; b y F a m e arid S i l b e r n i a n ~ as i ~ 189. I E; ; by Favrej as 189.0 E;,and by Berthelot and I,ouguinine+as 195.7 E;. -1ccepting Thoinsen’s valiie, as appearing on the whole the mo5t trustworthy, we find his titration of the acid depending upon the assnmption of the molecular weight of S a C l = j8.5and ; I g S 0 3= I 70, m-hile according to Clarke’s report of March, I 896,s these are to be taken as jS.06 and 168.69. Alpplyingthis correction to Thoinsen’s value for the heat of solution we have 190.6 K , In the present determinations the weight of acid was determined by weighing the tiibe full of acid before the esperinient and the fragments of the tube afterward. The)- therefore depend only upon the assumption of the molecular weight of HI (126.89). ;Iccepting this corrected value, and neglecting the sinal1 difference in the initial temperatures of Thornsen’s determinations (which were made at about 1 7 ” C), and those at present under discussion, we haye for the latent heat of the gas per gram molecule 42.3 K. One necessary correction to the above measiirements arises froin the tabes of acid being only about two-thirds full of the liquid. Xt the temperature of the experiment the liquid has a specific gra\ritJ. of 2 . 2 7 and the saturated vapor is iinder a pres-
’ P0g.g. .Inn.148,199 ( IS::’). - Ann. Chim. Phys. (j 37,412 (18j3). J
-I
Cortiptes rendus, 73, 973 ( I S ~ I ) , Ibid. 69, 630 (1b69). Jour. A 1 n ~Chem. . SOC. 18, 197 (1S96).
L i p i d Hj~d~~iodic Acid
495
siire of j . 5 atmospheres.' Assnining tlie \.apor to obey the ordinary gas law, the liquid will be 54 times as dense as the vapor3 and the latent heat being about one-third the heat of solution we ha\-e a correction (of some 0.3 percent to suhtract from our \-alue for the heat of :iol11tioI1; which brings it to 1q7.S E; and for tlie latent heat 42.8E:; or dropping tlie decimal as somenhat uncertain :
+
HI (liquid) Aq == HI.lq - 148 E;. HI (gas) = HI (liquid) + 43 I(.
Thomsen gives lis
H (gas)
+ I (solid) = H I (gas) - 60 K
which lipon recalculation with tlie atomic ~veightshere adopted becomes j9.9.practically identical with the former value. From these n-e obtain
H (gas) I I (solid) = H i (liquid) - 1 7 I;: that is to sa\-, liquid hydriodic acid at 12' C is still an endothermic compoiind lr-ith respect to solid iodin and hjdrogen utitier atinosplieric pressure : h i t its heat of decomposition is only a little over a quarter of that of the gaseoiis acid under atmospheric pressure. Z7iii:jenify of Cnlifoi-ilia, i l Z ( i ~zS9S ~3
' Daiiiriier.
Haiidhuch der :morganischeii Cheiiiie. I , jjj.
