1474
A N A L Y T I C A L CHEMISTRY
hours of opwatioii. \Vhen liquids w ~ r vir(-ulat,ed t ~ in thcx samplv and reference systems, no drift occurred, but some slight instabilities were caused by small bubbles passing along the interface. ;\t no time, however, wrre there deviations of niorp than 0.5 chart tlivision (0.00005 1t.I.) from the initial setting. Temperature Compensation. The main advarit age of the null balance system used in this instrument is to eliminate effects due l o tc~inperat~urr~ rhanges in the sample. By means of a suitable h w t cischanger the sample and reference liquid can be maintained :tt the same temperat,ure, which thereby reduces the degree of t enipcwt.ure control nrcessary. I f T I and , t t , are the refractive indexes of the sarnple :inti reference liquids, respectively, t hrrr thc. ctriitlit.iniis fw good rompensat,ion a r ~ : I!,
-
TI,
f 1.8 !.nI1,1,IP
20 -- ! l , . ~ r c f t w 1 w
20
(:OY(:LzIsIo\ r .
lht! refractomet,er provides a coiitiiiuous and accurate n i i ~ t l i o i l of iwording the refractive index of any liquid which does not h v i . :i tendency to deposit a film on a glass surface. Even a veq- t h i l i film will seriously interfere wit.h operation of the instrument. It i. independent of any coloration in the liquid. Very little n i : t i i i tenance is required, except for periodic cleaning of prisms ant1 I ' ~ L st.andardization, and it will operat,e for long periods of t,imr \vitlt ;it1 :icrur:iry nf better than +0.0001 refractive index unit. 4 C K N O W LEI)GAI ICNT
.ippreciatio1i is expressed to J. li;. Glarsuii mid Walter Sch\v:irtz K. Bowman for valuable comments: t i , I\'. A . Hariior and G . €1. Young for frimdly encouragemrwt : to t'w operative data; to J.
f I , l{, Stevenson of the Procter and Gamble Company, whn riiiiiiltanr~oudyTvorked n-jth reflrcted light type refractometers; : i n ( l t o John I*nvrtl, Jr., of the LTnertlOptical Company, Pittsburgh, Pa.. for. ni:iny helpful merhanic:tl s u g g e ~inn.: t (luring the construe-t i o i l of bhr instrument.
I)c.ttLctoi. ~:liiti~i~(~t~~i.i~tiCs must be the sanit~.
TIit. greater the deviat,ions from these conditions the poorer this twinpensation. The t,hird condit,ion can be satisfied closely, anii :tlso the first condition, depending upon specific conditions. The second and fourt,h conditions, however, can only be approximated, so that, in general, absolute temperature variat,ionsof nior(1 th:in 1 ' C. will seriously :tffec.t t8hracciir.:iry of thr. instrunic~ri(
L I T E H ~ T O K Kcrrm
I: H I ) I , I IMax, , "Optik," Ani1 Arbor, Mieh., Edwards Brothels. I !W3. (2) ( ' a r y . €1. H., Applied Ph;\,sics c:orporation, Pasadena, Calif.. 1111yuhlished report of use of this method. (::i)Fehruary 16, 1949. Contribution of niultiple industrial f d l o w . .hi], o f r h t , KPronst,rurtion F i n a n r ~Corliorntion. Offive of Rubhpr R z ' s i . r ~ c '
Pressure-Tight Infrared Absorption Cel for liquids Infrared spectroinetric anal?sis of mixtures of an) or 1111 of the CI olefins and paraffins in the liquid phase at rooin temperature has heeri impracticable because thin ahsorption cells could n o t he made tight enough to retain, without leakage, liquids haling high vapor pressures. itial?sis in the liquid phase has lieen considered as a means of a\ oiding inaccu racies resulting from 5anlplilIg a liquid mixture for anal?sis in the \apiir phase. The design and con-
r
r
HE an:ilysis 01 mixtures of an). or all of the (', olefins iind paraffins in the liquid phase at room temperature by infriii,ed sprvhomcbtrir niethods has heretofore been imprscticwhlt. I)(\( ~ u s thin r :iI)sorption cells could not be made tight enough t o ret win, without leakage, liquids having high vapor pressurc.~. in the liquid phase is a possible means of avoiding thc inaccwracies rc=sulting from the difficulty of securing it saniplr, in the vapor ph:tse which has the same composition :is thix liqiiiil in t h e container from which it \vas withdrawn ( 3 ) . I)ifficultic~sare also encouritercd in preventing t,he loss fi,oni liquid absorption cells of volatile solvents such B S ciirl)on tetrarhloritie and carbon disulfide with consequent change o f (*onoentration of solutions while recording their spectra. -1number of workers (.$, 7 , 8) have designed cells to hold volatile liquids, but, of the cells thin tmough to permit the study of' pure liquids without dilution in a solvent, onlj. those of Gildart :mi JVright ( 5 ) ,Benning, Ebert, and Irwin ( I ) , and Kiveiison (61 are tight at pressures appreciably above atmospheric. Of thest,. t8hc1:ittc.r two iised quartz windows arid sealiiig mpthods not ap-
strurtion of tight cells are descrihetl, ab well as the technique used in assembling arid testing them. The cells h a \ e rock salt windows and Mere sealed w i t h .irnalgam. The) ha\e been used at pressureu p t o 3.5 pounds per square inch gage for recording the spectra, from 1 to 1.5 microns, of the hutenes and 1,3-hirtaclieiie. The same cell serkes also to prevent loss o f tolatile solvent- from iolutions during the rec*ordingof spectra.
l)lir:il)l(~t o rock salt. :tnd tht. first did iiot liiive connections s u ~-t :it)lr. for tilling the cell and confining tht. sample under prwsurr. This piper describes the design, ronstruction, and technique n i :Lbwnit)lingcells using rock salt wintion-s, h s e d on the principlw 1)y (iildart and 11-right ( 5 ) . The cells have thickirrsstss ~lwrrit)c~:l I J t~" i n i 0.427 to 0.018 nmi. a n d have twen used a t pressures 111) t o :%.?Ipouricls per square inch (2.5 kg. J F I ' s ~c.m . ) gage to rerciril I h r d q)ec.tix of the liquid butenes and I,:3-hiitatli~nefrom 1 t o 1.5 iniri,ons :it room tmiperatiiw ( 2 ) . DESIGN A Y I ) COXSTHUCTION
The c . t s l l Ir:tnies ivew desigiied to fit t h e cell holder of l'wkiiiLlmer bpectronieters. The)- \\-tire made of steel and somt~\vliat heavier than nolmnl t o nlinimizc~ possiblc deformation r u i i l c ~ r . pressurta.
Prrliniitiaq- trials indicated that leaks wuld be made Irslikely by inrreasing the length of thr potential leak path. To provide for this and also to minimize stresses in the wintlo\w. the filling holes were drilled thrnugh one of the windows nornix1 to its suiTace. Because it was drsiFed not to intercept any of t h ( , iwnc of radiation whirh rould pass the usual 21-mm. dianir~tc~i
1475
V O L U M E 21, NO. 12, D E C E M B E R 1 9 4 9
nnm. in diameter and 8.:5.nlm. thick). The dimensions and general character of the metsl fil.linps (union-type connect,ions and needle valves developed :It tla! Stttionsl Bureau of Standards t,? H. F. Stimson) which it IVRS qlrsircd t,o use to connect snmplo cllinders t,o cells were such tliat c.oniwr:t,ionsto the cover pinte (communicating through it tu thr lrolrs iii bhe upper salt window) were, made radial rather ~thmi mimal t,a its surface to avoid interrepting portions of the beam. There was insufficient room to connect tubing a t the bot.loni when the cell frame u-as ill rmsition u,ith its connections verl,ieal,
sauds of t,he base plate, to permit. orienbstion of the tilling holes m d bhreaded connretions in B Ltectl, H , or in u vertical, J , position as desired. The diameier. of the u,indow opening betmeea the two straight sidt-s was made large enough to permit use of the full height, of the slit with thc connections vertical. Canneet.ion to tubing was made by niems of brass ells, K , machined to fit,, and s\VeHtod into holes in the eover plate with soft solder, after which the inner faro of the cover plate wa,s machined flat. and polistied, the inner ends of the ells being Hush :tnd forming a continuous surface wit,h the face of the plate. The 1-mm. passage through the ell was enlarged to &: depth of 3 or 4 mm. a t the outar t,hroaded end, L, to permit entry of the t,ip of the stainless steel cone fitt,ing, M, which formed the seat for the connection to t,ubing. The stainless st,eel cone fitting was silversoldered to the '/8-inch outside diampter copper t,ubing yit,h whirh the connwtmns were made.
&&hrri Cohequentfy, in thia.ny of these material-. The spacer, D,brtwmx the two windows, C and E , was n d r i h r spacer or gmket het,&ren t& pieces ai plate g h s . Higg of lead sheet. excent Ita: thinnest. which was tin foil 0.0005 inch spots may be made apparent by twisting tho upper piece of glass ~~
~~~~
~
D~
~
sll the way t h u g 6 wilh ve?? little chipping at the edges of thc hole on either side of thc window. Any resistance to turning can be felt easily and undue force which might split or chip t,he Findow can be avoided. Tho gasket, F,betweon the drilled window and the cover plal,c, G, was made of lead sheet thick enough for convenient handling. The two holes were punched with n jeweler's punch and the hurl was rpmoved by judicious scraping, followed by pressing hrt,wcen plate glass to ensure flatness and to detect high spots. Thc cover plate, 0,ivas drilled n i t h two sets of holes for ihc
LL smafl wzd of cotton &ist&d k i t h c a h o n tebachloride: Tho amalgamation and assembly should be done promptly. The
dawn on the rock salt window, and the newly expdsed surface
Figure 1. Parts and Alternative Assembly of a Tight Infrared Absorption Cell for Liqirids IIaring Vapor Pressures Up to 35 P o t I d a per Square Inch Gage Wiuduwxitra rock s a l t aesled with amaleem
One of the eannretions t u the cell was capped nnd the other connected t,o a cylinder of compressed gas through :I pressure regulator.
ANALYTICAL CHEMISTRY
1476
The cell was immersed in carbon tetrachloride and the pressure gradually increased. Extremely small bubbles are usually formed and rise in a fine stream, which can be detected easily in a good light. IVhen a leak was found the cell was removed from the carbon tetrachloride and the nuts were loosened gradually Kith the cell under moderate pressure. The spreading leak gradually separated the window from the spacer (or the gasket from the cover plate) as the confining pressure was relieved. The cell was then taken apart only a t the layer of separation, the faulty surface reamalgamated as before, the cell reassembled and allowed to set, and retested. This process was repeated until no leaks were detected a t 35 pounds per square inch gage. This was the maximum pressure deemed advisable for use with the present loading springs. Stronger springs would permit higher pressures. The maximum safe pressure for salt ~ i n d o w s6.5 mm. thick has not been determined. DISCUSSIOU
It is not advisable to attempt to use a cell that leaks even slightly, for the leak is likely to spread and the sharp local chilling resulting from the evaporation of liquid in the leak may crack both windows. The experience of the authors in this respect has convinced them that the crack results from the leak, not the reverse. Such a crack can liberate enough flammable gas to constitute a fire hazard. After a period of use, the liquid penetrated slightly into cracks in the brittle tin amalgam a t the confining edge of the spacer. The expansion accompanying release of pressure during elimination of bubbles while filling, or when emptying or evacuating, has caused small fragments of the confining edge of very thin spacers to separate slightly. This process may eventually progress to the point where leakage will occur. This behavior is not expected to occur with thicker spacers where there is a core of unamalgamated metal left to hold the brittle surfaces intact. It seems advisable, therefore, to test by immersion from time to time cells which show such behavior, thus minimiz-
ing the possibility of a Iedk breaking through while in use. hfter testing, the thickness of the cells was determined by the interference method described by Smith and hliller (8). The effect of the internal pressure on the thickness of one of the cells was evaluated by determining the thickness before and while the cell was subjected to 25 pounds per square inch gage with oxygen. The increase amounted to 0.0004 mm., about O.l%of the 0.427-mm. cell or 47, of the thinnest cell. When it is desired to use the cells for solutions and to fill thy rells from the bottom, the change of orientation of the connections from a lateral to a vertical position is readily accomplished by removing the nuts and springs, lifting the cover plate and window assembly as a unit from the studs, rotating through go", and replacing them in the desired position without impairing the tightness of the cell. The cells may be cleaned readily without taking them apart b j applying suction to one connection and flushing with solvent from a medicine dropper. When it becomes necessary to repolish the windows, a separation a t the least perfect bond may be accomplished as described above in connection with curing leaks. d tightly adhering spacer or gasket, thus exposed on one side, may be removed without damage to the window by disintegration in excess mercury. LITERATURE CITED
(1) Benning, A. F., Ebert, A . A., and Irwin, C. F., ANAL.CHEM.,19 867 (1947). (2) Creita, E. C., and Smith, Francis A., J . Research .\-atl. Bur Standards, 43,365(1949); RP2031. (3) Dibeler, V. H., and Mohler, F. L., J . Research iVat2. Bur. Standards, 39, 149 (1947); RP 1818. (4) Fry, D. L., Nusbaum, R. E., and Randall, H. hl., J . Applied Phys., 17, 151 (1946). ( 5 ) Gildart, L., and Wright, N., Rev.Sci. Instruments, 12, 204 (1941) (6) Kivenson, Gilbert, J . Optical SOC.Am., 39,484 (1949.) (7) Oetjen, R. A., Ward, W. M., and Robinson, J. A., Ibid., 36, 615 (1946). 18) Smith, D. C., and Miller, E. C., Ibid., 34,130 (1944).
RECEIPEDJune 15, 1949
Determination of Carbon Monoxide in Hydrocarbon Gases Containing Olefins PAUL R. THOMAS, LEON DO"',
AND
HARRY LEVIN
Beacon Laboratory, The Texas Company, Beacon, N . Y .
S
TUDIES of hydrocarbon bynthesis and catalytic cracking made it necessary to determine carbon monoxide in gases that contain large quantities of olefins. Numerous methods have been published for the determination of carbon monoxide. but they are not suitable for samples containing olefins. Colorimetric methods (4, 8) have been used for the determination of carbon monoxide in concentrations less than 1%. Heated cupric oxide ( 1 ) has been employed for oxidizing carbon monoxide to carbon dioxide. However, hydrogen and some paraffin hydrocarbons are also oxidized a t the temperature necessary to oxidize carbon monoxide completely. Teague (16) determined carbon monoxide iodometrically in motor exhaust gas, employing iodine pentoxide for the oxidation, a i t h a precision of 0.003% for samples containing 0.01 to 0.1%. Larson and Whittaker (10) hydrogenated carbon monoxide over nickel catalyst a t a temperature of 290" to 310" C. McCullough et al. (11) oxidized the gas with red mercuric oxide a t elevated temperature.
' Prefient address, Jefferson
Chemiasl Company, S e w York, N Y
Some of the reagents more commonly employed for the absorption of carbon monoxide are acid cuprous chloride, ammoniacal cuprous chloride, and a suspension of 2-naphthol in acid cuprous sulfate. These reagents were reported to dissolve olefins (6), and Table I illustrates this solubility. They must be removed before the determination of carbon monoxide. All the above methods depend on the absence of unsaturated hydrocarbon gases. For the removal of unsaturates, sulfuric acid and bromine water have been commonly used. Fuming sulfuric acid and silver sulfate-activated sulfuric acid (7, 16) were found unsuccessful in this laboratory for the removal of ethene from ethene-hydrogen mixtures. Results in Table I1 show that even after 47 passes not all the ethene was absorbed. Incompleteness of absorption was confirmed by hydrogenation of the gases remaining after sulfuric acid treatment of an ethene-hydrogen mixture. Francis and Lukasiewicz ( 6 ) absorbed ethene in mercuric sulfatesulfuric acid reagent, but Brooks et al. ( 2 ) found this reagent slowly oxidizes carbon mon-
