n i c w u r y in BO. M~Iirn it is sup(+ atniosl)licric S C l is closed anti SC3 is opened t o C to lileed off the excess pre~sure. (Ikcause C is a very fine capillary. 1)ack-tIiffusion of air is unimportant. If C is iniiiicrsed in a licaker of water. one can readily tell when tlw pressure is atmospheric.) Tlmr pressurc is t h m clieckcd by closing SC:3. opvning S C 2 , and rccording the Iivight tlifferttnci?: if any. in the oil maiiomrtrr. Thcn SC2 is closed, -4 and -5 are o p e n d , anti the mercury is raiwil in R iint'il the height diffcrencc in L B aiitl R intlicatm that the pressurt' is again near atinosphcric. (The volumc of I' should have I t e n adjusted so that' this is near thc top of R.) Let us call this point R?. Tlion SC2 is openrd cautiously t o set' if the pressure is equal t o the initial rcading. If not', the nicrcury I t v ~ in l R is adjustcil so that tlic rtbatling on .112 is \i.itliiii 0.5 mni. of the initial reatling. If' tliere has been 110 cliangc in tcnipcrature or atmospheric prcssurv i i i tlw tiiiie rrquircd for tlic olwrvations a t R, ant1 Ry-i.c.. about 2 minutvs-tlic volume of mercury I)etn-cwi R, and R?reprcwnts the vo!umc nicasurenients can be readily csarried out in t,riplicate, because rcvvacuat'ion to a tolerablc jm'ssiirc takes o n l y ahout 3 minutes. Thc reproducihility of triplicatc runs is gcwrally licttrr tliaii =2 mm. in R?. On the tiasis of the calilirated diameter of the> capillary. this Imicans an error of aboiit -0.0015 c r . in a total volume of 8 rr. Thc alio\.c procedure i5 rcpcatcd with tlic saiiiple~ i n T and the level of the mcmxiry in R is now detcrmined to be R3. Thc tlifferrnce in volume lietwen R2 and R3 reprcscnts the rolunie of t,hc sample. arid from thc n-eight the density ?a11 lir tlrternminrtl.
Table
I.
Snnmple S i shot i :C~Q
Density Determinations
Ilensity, C+./Cc. Lit. Detd. 8.90 8.93 1 , 989b 1,980c 1.06Yd
1, 9 8 2
1 .9iGe Hg 13.536 13.525 KC1 dried at 140' C. T7alue reported (5') for fused KC1 :it Q
20° c
c.
1-alura obtained on same sample on
different days xhen ambient conditions w r e different.
Value reported ( 5 ) for KC1 at 22" C. after drying in vacuo at 160" C. e Different samplc from same batch as C.
For investigations on catalj sts it is oft?:: dcsirahle to obtain densities with both helium and mercury as the displacing fluid. The difference in these t n o can lie used t o calculate rore volume ( I ) . Although tlie apparatus n a s not actually uscd for this I)urpose, it swms clear that rntwury densities can he obtained by using T as a pycnometer. T can be filled after evacuation by raising LB, so that thc mercury floir s o w r the top of R into T . Results of helium d.nsit! dcterminations for s c v r a l materials are shon n in Table I. On the basis of the detrrniinations of mercury and nickel the accuracy ould appear to be n ithin 0.37,. The case for potassium chloride is not so clear, but w e n in this case the results appear good to about +0,5%. The error in density measurements for any solid depends on the amount of free space in the sample tube; hence,
for a fised-volume pycnomctcr, the error increases n i t h decreasing bulk density. Variations in atmospheric pressure and temperature from run to run are unimportant and errors from this source can be expected only for variations nithin a given run. The results nith potassium chloride bear this out. The same sample examined on diffuent da! s uiider different ambient conditions gave results in agreement t o 1 part in 1000. Check runs n i t h different samplc s agreed to nithin about 2 parts in 1000. This ap~iaratusappears to offu :I promising method for studying c1iangc.s in dcnsity n i t h pretri~itnient. If T and P are the same tcmperaturc, the rcading error will be independent of snniple size; hcncc, 111 principle, volume changes nith, say, hvat treatment on a sample having a volumc of 100 cc. can be detcrmined to 10 1i.p.m. Such accuracy nil1 be attainable if the baronictric pressure is constant during the time required for t h t nieasiircnicnts and the level In the oil manomcter is adjusted to 0.1 nim. LITERATURE CITED
(1) .inderson, It. B., Hall, W.K., Hofer, L. J. E., J . Am. Chem. Sac. 70, 2465 (1948). ( 2 ) Kokes, R. J., Emmett, P. H.?Ibsd., 81,5032 (1959). (:i) Reilley, J., Rae, JV. S., "Physicochemical Methoc
Chem. 166. 257 (1957). (6) Smith, R. C., Jr., Howard, H. C., Ind. Eng. Chem. 34,438 (1912). \
I
A Heater for Gas Chromatographic Columns John N. Roper, Jr., Research Laboratories, Tennessee Eastman Co., Division of Eastman Kodak Co., Kingsport, Tenn.
channeling ivould occur. The column has no nrapped-on heating clement or insulation, so it is easily replaccd or repacked. The heating rate, because of the low lieat capacity of the furnacc, is almost as, fast as if the heating cleiiieiit were n.rapped 011 the column. This makes the apparatus easily adxptahle to the programmed temperaturc-risc technique [Dal Sogare, S..I h i n e t t . C.E,, *Ix.~L. CHEJI.30, 1157 1 1 9 S ) ] saiid it is simple to go quickly froin one opcr:tting temperature to anothcr. The temperature staliilitj- i,s wrprising1)- good, K i t h a minimum of manual control of variablc-wltage transformer scttings. tlie olicrating temlmxture vniies 110 niore than 2" or 3" C. in 9 hours: :inti no cliarige greater than 1' C. 1)cr hour hns Iiecii ohservcd. This is not stnhir enougli for qwntita-
tive peak-height tletcrminations, but it is sufficient for qu:ilitatiT-c work when the method of acldiiig a known compound for peak identification is used or when peak arca is measured for quantitative determinations. CONSTRUCTION OF FURNACE
Thc furnace, niaile from stainless st'eel tuhing. is shon.n in Figure 1. The open ends of t!iP t'ulic, arc. closi'd with dainlcss steel split circl(+ attachcd by s c r e w through overlapping mrs. A . Onc of the ~ n piccc~s d on the l o n - c ~half of the furnacc is flanged for attachment to the dctcctor 1mitc.r litis 1)y slicet metal s c r r m , B . The picccs attached to the uppcr half an' slottrd t o acconimodatc the tuhiiig going to and from the column, so t,hnt the furnace may be opened for rapid cooling n-hilc the column is in placi'. A slottcd, arlj ustahlc suDport,ing nicinlirr. C. is (3rd
VOL. 32, NO. 3, MARCH 1960
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