+
depression of tlic actlvity mid lierice tlic melting point comes a bout c4'cctivcly oi ily through "dilution" of the electroiis in tlie nictallic conduction band. Uiifortuiiately, the quantitative cryoscopic treatment in this case is iiot obvious. Consequently the inter\.ciiiiig "AHf" values obtaiiicd for Cc12 aiid I'rIn call incrcly be takcii as indicative of the intermediate character of tlicsc iiiclts, with a grcatcr teiidciicy toward localizatioii of tlic clcctroii i i i liquid l'r12. Ttic ability of competiiig cloctroiiic states to coexist iii solutions, of course, allows inorc subtlc trends to tic obscrvcd than is possit)lc iii p u i ~solids. I n coinparison t o tlic wsults i n lig. 1, the apparelit lirat obtaiiicd a h v c for Cc12 sceiiis somewhat low,
since the coiiductivity in tlic iiiorc dilute CcIJ Cc solutioiis is actually slightly greater tliaii with laiitlianurn. This inay be the result of only a different coiicentratioii dcpeiideiice of the conductivity in the two cases iii the iiit~crvciiirig regioii. .Uternatively, an apparelit hcat up to about 40 kcal. i i i ~ l c - could ~ obtaiiicd by a more subjective recoiistruction of tho liquidus curve tlirough a greater thaii usual scatter of cxperinieiital poiiits so as to give ail iiiitially sinallcr rate of frecziiig point dcpressioii. conductivity data for niorc coilcentrated solutioiis as well as for the solids at liiglier tciiiperaturcs will be useful here as well as i i i asscssiiig inore clearly tlie character of liquid 15-12.
Introduction Tho heat of foriiiatioii of hydrogcii fiuoridc plays a role iii fluoriiic: t)oiiib aiid flaiiic caloriiuctry aiialogous to thc rola played hy the hcat of foriliatioil of water iii oxygeii t)oiiih aiid flanic caloriiwtry. As iiriiistroiigl has stated, "111 tho valiit: for tho [hcat of fornutioil of I-Ilc(g)I, coinbiiictd with tho heat of solutioii of gaseous hydrogeii fluoridc iii water, lies thc koy to much of thc existciit litcraturc of the thcriiiochciiiistry of fluorine coiiipouiids, dcpciidciit as it has t)ccii upoii the calorimetric study of rcactioiis of aquctous solutioiis of hydrogcii fluoridc." It is cwxit'ial for progress i i i fhoriiic therinochciiiistry that the staiidard hcat of foriliatioil of hydrogen fluoridt: gas should lxt dctcriiiiiicd ivith good That t,he goal prccisioii arid hy ~ i i o r ct,hnii 0 1 ~ iiicthod. : has iiot yet t)cclii achiovcd is cvidciit iii 'l'ablc I , ivhioh of the cluaiitit'y.2-"1 contaiiis thc iiiodorii d(?t(!riiiiti~tioiis lis iiidicatctl by thc last t:iif.ry i i i thc tablc, a coiisidcrahlc part' of tho variatioii of t8hcrcportcd rcsu1t.s arises froin t'hc \.cry uiicctitaiii corroetioii for thc iiiipcrfcotioii of hydrogcii iluoiidc gas u t rooiii tciiipcmturc. I n 1932
thc coiiipilcis of Circular 500" sclcctrd a value of JIZj''2se (-G4,2 k e d . iiiok-') \\ hlch rcplcsclitcd the bcst cstiniatc availablt. a t that tiiiic. More rcccntly .Irinstroiig' cited evidence that the r(>coiiiinendcd value should be replaced by a inore iicgativc one. It is not the purpose of this paper to discuss the rclativc iiierits of the results of previous cxpcriiiieiital incthods. Rather, the purpose is to poiiit out that ivith the advent of high prccisioii fluoriiic bomb calorinictryl2-I7 it is iiow possible to reverse thc usual procedure of coinputiiig the heat of forinatioii of ccrtaiii fluorides from that of hydrogcii fluoride, and, illstead, to obtain the hcat of forinatioii of hydrogen fluoride by coinbination of the nicasui*cd heats of ccrtaiii ~ ~ 1 1 dcfiiicd i.eactioiis. l'hc following arc cxaiiiplcs of such schcnics.
(1) C;. 'r. A r i ~ ~ s t r mI Ii I~",~ ' ~ s i l ~ ~ T i l i I ~ ! : i 't i~i i I i ~ ~ r ~ ~ ~ ~ ~ cV Iu l~. e11, i i11. i i ,I. ~ t ~ ~ , " Skinner, Editor, lnt(~rscicweViibIisl~[~rb, I n o . , Ncn. Y u r k . N.Y.,l!)tiY, 11. 1.1 1. ( 2 ) 11. 1.m \Vartclibcrg and 0 . l.'itziieir %. U , I O I ' L I .n i l y e i n . C h e n . , 161, 313 (10263). (io
0.I l U f E ILUd M'. > I P l l Z ( ' l , i h i d . , 196, 373 (1!):
