Oct., 1914
T H E J O L - R L Y A L O F I N D C ' S T R I A L A N D ENGILTTEERING C H E M I S T R Y
vapor t o form sulfuric acid which condenses in t h e packing in t h e exit end of t h e combustion tube. The zinc t u b e prevents a n y sulfuric acid t h u s formed from entering t h e absorption tube, b u t the bulk of i t condenses in t h e cold end of the combustion tube. I t is important t o burn out this accumulation after making about j o combustions, in t h e following manner: Disconnect t h e stopper from t h e exit end of t h e tube a n d pull t h e latter forward so t h a t t h e exit end is heated t o t h e temperature of t h e furnace. Keep a slow stream of oxygen passing through t h e t u b e until t h e fumes of sulfuric anhydride are no longer visible. This takes b u t a few minutes each day, a n d ensures better results. When the supply of oxygen is correctly adjusted about nine minutes should elapse between the time t h e boat is inserted and t h e first appearance of turbidity in t h e absorption flask. The titration with standard hydrochloric acid should be accompanied by thorough agitation of t h e flask. The last j or I O cc. should be r u n in rather slowly. CHEMICAL LABORATORY STEEL COMPAKY ILLIKOIS ILL. SOUTHCHICAGO,
84 5
so t h a t t h e absorption proceeds rapidly. Of t h e slower-absorbing reagents, cuprous chloride for CO has been eliminated a n d alkaline pyrogallate for absorbing oxygen in t h e concentration usually found in gases. t o which this apparatus is particularly adapted, does not consume much time. The small quantity of reagent has t h e advantage of reducing t o a minimum solution of other gases not intended t o be absorbed by t h a t reagent. For example, fuming sulfuric acid appreciably attacks paraffin hydrocarbons higher in t h e series t h a n CH4 a n d may cause errors in either t h e Hempel or Orsat apparatus.' Using about 3 cc. fuming acid in t h e apparatus here described, 7 3 . j cc. of Pittsburgh natural gas ( n = I . 16 in C,H2,+,) passed into t h e pipette j times and allowed t o s t a n d 5 minutes gave a contraction of o . o j cc.; similarly 4 0 cc. of a n *oil gas ( n = I . 61), in which homologs higher t h a n methane predominated, showed 0 . 0 7 cc. contraction, neither of which much exceeds t h e error of reading. D E T E R U I K A T I O S OP HYDROGEN AND C A R B O S MONOXIDE
BY
FRACTIOXAL
COMBUSTION
WITH
COPPER
OXIDE
AN APPARATUS FOR THE ANALYSIS OF COMPLEX GAS MIXTURES' By GUY B. TAYLOR Received July 7 , 1914
I n making a s t u d y of t h e gases evolved from coal at various temperatures, i t has been found necessary t o make analyses of gases of very complex composition. The usual forms of apparatus described in the gas manuals are accurate enough for mixtures containing only a few simple constituents, or for technical work where great accuracy is not required. Most of these methods require separate portions for t h e estimation of hydrogen a n d saturated paraffin hydrocarbons, since one complete combustion permits of t h e calculation t o hydrogen a n d one hydrocarbon only. Even commercial coal gas contains appreciable quantities of homologs higher t h a n CHI, a n d calculation of t h e combustion d a t a t o hydrogen a n d methane only is open t o question. Bone a n d Wheeler2 have described a n apparatus for t h e analysis of complex gases in which t h e absorptions are carried o u t i n ' a single pipette with fresh reagent for each absorption a n d in which t h e changes caused b y these absorptions are measured at constant volume b y difference in pressure. I n t h e apparatus described here, use of t h e Bone a n d Wheeler method of absorption has been combined with t h e usual form of compensated burette ( A ) , Fig. I , a copperoxide U-tube for t h e estimation of hydrogen a n d carbon monoxide ( C ) , a n d a slow-combustion pipette ( B ) for burning hydrocarbons. T h e absorption vessels ( D , E ) dip into a wooden trough containing mercury. The reagents are introduced b y means of curved pipettes under t h e lower edge a n d after use are discharged into G b y applying suction at g. Although t h e surface exposed t o t h e gas in not very great, this is largely offset b y t h e use of fresh reagents Published by permission of the Director. C. S. Bureau of Mines. ?Jour. SOC.Chem. I n d . , 2T (1908). 10. I
I t has been found in this laboratory t h a t for crude, unwashed gases from low-temperature distillations of coal, t h e methods for estimating hydrogen depend-
FIG.I
ing on t h e catalytic action of palladium, such as palladium black or colloidal liquid absorbents, are unsatisfactory a n d in most cases fail entirely. If a mixture of CO, Hz, a n d hydrocarbons of t h e , absence of oxygen, be passed over series C n H ~ n + 2in copper oxide heated t o about z j o o C., t h e CO may be burned quantitatively t o COz a n d t h e hydrogen t o water, while t h e hydrocarbons are untouched, in which case t h e contraction in volume is equal t o t h e hydrogen present, a n d t h e C o n formed equals the CO in t h e mixture. Nesmjelow2 determines these t w o gases simultaneously with CuO in t h e presence of oxygen, in which case t h e equivalent oxygen necessary for t h e oxidation disappears, t h e CuO acting in intermediary or 1
Compare Burrell and Seibert, Bullelin 42, Bureau of Mines, p. 46. anal. Chem., 48 (1909), 232.
* Zeit.
'
'346
I
T H E J O U R N A L OF I i V D C S T R I A L A N D E N G I N E E R I Y G C H E M I S T R Y
catalytic capacity. Since t h e oxide itself furnishes t h e required oxygen this is unnecessary. I n Fig. I , t h e inverted U-tube C is about j m m . internal diameter a n d contains 3-4 g. of a mixture of fine and coarse cupric oxide, which is prevented Sy glass wool plugs from getting into t h e capillary connections. One capillary is sealed on before t h e tube is filled a n d t h e other afterward. The gas volume of t h e tube need not exceed 2 cc. It is seldom necessary t o renew t h e copper oxide if t h e tube is removed a n d gently heated over a free flame, while a current of air is being blown through i t , until t h e bright specks of reduced copper become oxidized. I t is advisable t o revive t h e oxide t h u s after three or four times use. T h e inverted position is chosen t o prevent danger of cracking from water .running back into t h e heated part. T E M P E R A T U R E O F T H E CuO-Jaeger,' t h e originator of t h e method for hydrogen, set t h e temperature a t 250' C.; Ubbelholde a n d de Castro2 fix i t a t 2 7 0 ° , which is t h e temperature advocated by The method of taking temperature by putting a thermometer bulb in a n oven a n d leaving a long emergent stem may be many degrees in error. The exact temperature t h a t can be used will depend upon t h e n a t u r e of t h e hydrocarbons present. With CHI only. 300' is probably not too high. but a t this temperature there is danger of oxidation of t h e higher homologs of CHI. We have obtained satisfactory results with t h e thermometer bulb next t h e U-tube in a small electrically heated oven a t 2 7 j " for gases in which t h e average value of $ 2 in C n H z n + 2 was as high as I . 6 j. This oven may be simply constructed in any laboratory a n d a few preliminary experiments will determine what temperature on t h e thermometer between 2 j 0 O a n d 300° works best for t h e gases t o be analyzed, then by noting t h e current required t h e heating conditions may be exactly reproduced for each For constructing t h e heater take two glass , analysis. tubes, 3 j m m . diameter, a n d bind them together side b y side. Around t h e two tubes wrap several thicknesses of heavy paper. Over t h e paper wind No. 20 nichrome or "Climax" wire z mm. between turns for about a I O cm. length on t h e tubes. This gives a n oval-shaped heating coil around which t h e oven is t o be built. After fastening t h e ends, which should be twisted double t o serve as leads, wrap a layer of wetted, thick asbestos paper tightly around t h e coil a n d fasten i t with copper wire wound between t h e resistance wire turns. Then cover with a thin paste of magnesium-oxide-sodium-silicate cement a n d paste on several layers more of asbestos paper. The oven may be dried out a t once over a free flame, which bakes t h e wire covering hard a n d chars t h e inside paper so t h a t t h e glass tubes may be removed. The oven is completed by wrapping loosely several layers of asbestos board for heat insulation, covering t h e ends a n d cutting a slit in one of them for t h e entrance of t h e U-tube. 1
2
3
Jour. Gasbeleuchlung, 41 (1898i, i 6 4 . I b i d . , 64 (1911), 810. "Gas Analysis," .I M . Dennis (Macmillan. 1913). p. 201.
1-01. 6 , X o .
IO
TESTS O F T H E METHOD-In Table 1 are given some of t h e results obtained b y t h e method of fractional combustion, v?hich shows t h a t not only may hydrogen and carbon monoxide be burned in the presence of methane without danger of oxidation of t h e latter b u t also in the presence of high concentrations of higher paraffins. The hydrogen was prepared b y electrolysis and passed over a glowing platinum spiral to. remove traces of oxygen. The C O was prepared from oxalic a n d sulfuric acids, purified a n d analyzed by combustion with oxygen. Hydrocarbon gas ( a ) was Pittsburgh natural gas in which t h e average value of 12 in C n H 2 n + 2 determined from t h e combustion d a t a was I . 1 6 . Analyses of this gas in t h e Bureau's laboratories by fractional condensation have shown t h a t i t contains both ethane a n d propane.' Gas ( b ) is a natural oil gas ( n = 1.61) in which homologs higher t h a n methane predominate. TABLE I Cc. taken
co 12.30 34.10 17.35 0.0 0.0 0.0 4.40 14.80
Hz 0.0 0.0 0.0 20.45 15.20 50.40 7.10 2 3 . 75
. CnH2n + 2 35.0 a 34.6 a 49.3 b 38.8 b 59.2 b 39.1 b 44.0 b 43.5 b
-
Cc. found
CO? formed = CO 12.35 3:. i o 11.30 0.0 0.0 0.0 4.40 14.55
Contraction = HP 0.0 0.0
0.0 20.45 15.25 50.30 7.10 23,80
I n a n artificial mixture containing approximately per cent H?, I j per cent CO, a n d 1 7 per cent Pittsburgh natural gas, was found by analysis 1 4 . 6 per cent CO by absorption with ammoniacal cuprous chloride and 1 4 . 6j per cent CO by t h e CuO combustion method, j 2 . o per cent H? b y CuO after absorbing CO, a n d j 2 . I per cent determined simultaneously with CO by t h e combustion method. The time required for t h e complete burning of t h e hydrogen a n d carbon monoxide does not seem t o be a function of t h e quantities present, as much as t h e nature of t h e gas mixture. For ordinary illuminating or producer gas, t h e hydrogen is usually completely removed in 6-10 slow passes over t h e CuO. With some low-temperature coal distillates, not scrubbed, we have consumed as high as 40 minutes removing 3 - j cc. I n general, when t h e contraction due t o t h e burning of t h e hydrogen has.ceased t h e CO may be assumed t o have been also completely oxidized, unless it be present in much greater concentration t h a n t h e hydrogen, in which case passage through the C u O tube should be continued some minutes longer. An increase in volume occurring at any time during t h e operation may be due t o combustion of higher hydrocarbons. I n general, it may be stated t h a t t h e time required for t h e estimation of these two constituents b y this method is shorter t h a n any direct absorption method for CO alone. j 2
P R O C E D U R E FOR ANALYSIS O F C O A L GAS
The reagents needed are 3 0 per cent KOH, potassium pyrogallate solution, a n d fuming sulfuric acid. The first t w o are prepared in quantity and stored in protected bottles with glass siphons leading t o rubber 1
Burrell and Seibert, Loc. c i t . , pp. 91-96.
Oct.. 1914
T H E J O l ' R S d L O F I - V D L ' S T H I A L . L 9 D E.VGISEERI-1-G C H E M I S T R Y
tubes provided with pinch cocks a n d glass tips. These tips are t u r n e d u p a t t h e end (Fig. 11) a n d t h e reagent delivered b y gravity into t h e absorption pipette. F o r washing o u t t h e pipette. bottles of water a n d j per cent ' sulfuric acid are similarly arranged. At the beginning of an analysis t h e t u b e C is filled with air a n d t h e T stopcocks turned so a s t o by-pass C. T h e burette (whose walls are, of course, k e p t w e t ) , t h e vessels B, D, E , a n d all FIG. I1 connecting capillaries are filled with mercury. T h e sample is t a k e n into t h e burette a t a . T h e calibration marks on t h e burette include t h e volume from t h e stopcock h . T h e volume of t h e capillary space from b to d is also known. After ascertaining t h e volume of t h e sample, r u n t h e gas into D a n d b y lowering t h e leveling bulb on t h e b u r e t t e . set t h e mercu'ry meniscus on a m a r k just under t h e stopcock d . S o w introduce 3-j cc. K O H , pass t h e gas into t h e pipette seve.ral times, bring back t o t h e mark d . a n d read t h e contraction in volume equal t o t h e CO, in t h e gas. Bring t h e K O H t o k a n d discharge t h e reagent i n t o G, a n d after washing D reset t h e mercury t h r e a d a t d . T h e reading should not have changed. Introduce 2-3 cc. of fuming acid b y means of a curved pipette a n d absorb t h e illuminants. After discharging t h e acid, t h e wash water, which is acid. should be r u n through t h e bore of t h e stopcock i t k a n d a little way i n t o t h e capillary connecting with t h e b u r e t t e , in order t o make sure t h a t no alkali is left t o foul t h e tubes. A t this point t h e a d d e d precaution should be t a k e n of thoroughly rinsing both pipettes with dilute acid. Reset t o t h e m a r k d a n d introduce a b o u t cc. K O H for absorbing t h e fumes from t h e previous reagent. Extreme care m u s t now be t a k e n t o avoid a n y alkali rising above d until after t h e hydrogen has been determined. Without removing t h e K O H introduce 5-6 cc. pyrogallate solution a n d absorb t h e ox ygen. T h e gases remaining. ( C O , HP. C H I . C2H6, etc.1 are determined b y combustion. Communication through C having been established b y properly t u r n ing t h e T stopcocks, a number of passes of t h e gas i n t o t h e pyrogallate pipette D are made t o remove completely t h e oxygen in C. iYow bring t h e heater over C a n d establish t h e t e m p e r a t u r e a t a b o u t 2 7 j '. Pass t h e gas back a n d forth between t h e burette a n d t h e vessel E until there is n o more contraction in volume. Bring t h e mercury from E t o t h e point h , remove t h e heater from C a n d allow t o cool. T h e observed contraction equals t h e hydrogen. Since t h e gas is free from oxygen, t h e COz formed m a y be absorbed in t h e pyrogallate a n d equals t h e C O present in t h e sample. T u r n t h e T stopcocks back t o their original position. Discharge t h e reagent f r o m D a n d thoroughly wash with dilute acid. R u n t h e residual gas completely into D , filling all t h e capillaries again with mercury, D r a w into t h e burette 9j-100 C C . of oxygen and
847
without noting its exact volume r u n most of i t into E , connect . C again a n d bring back t h e oxygen through it into t h e burette t o wash out t h e combustible gases, leaving C filled with oxygen. Open t h e by-pass, cutting o u t C , a n d bring t h e mercury t o b for measurem e n t of t h e volume of t h e oxygen, which is t h e n run into t h e combustion pipette B. Bring t h e gas in D back into t h e burette a n d make t h e usual slow combustion for hydrocarbon.' noting t h e contraction and CO, produced. Attention is called t o t h e fact t h a t t h e gas must always be r u n into t h e oxygen a n d never in t h e reverse order, since t h e higher hydrocarbons are decomposed with deposition of carbon b y t h e glowing platinum wire. I n t h e method here described of clearing t h e copper-oxide t u b e of hydrocarbons, care must be t a k e n never t o obtain a n explosive mixture. If t h e gas volume of t h e t u b e does not exceed 2 cc. a n d a t least 9 j cc. of oxygen are used, there is no danger of this .occurring. T h e combustion d a t a m a y be calculated t o C H I a n d C2H, b y applying equations based on contraction and C o n produced,2 b u t perhaps a better way is t h a t suggested b y Earnshaw3 a n d used in this laboratory. T h e general equation for t h e combustion of hydrocarbons of t h e series CnH2n+2 is
If t h e volume of C n H 2 n + 2be called V , t h e COn produced A, a n d t h e contraction C , t h e n A = nV 2
or
c
=
) , ( V
+3
1%
1j
T h e above detailed procedure has been given in order t o indicate a method of manipulation t h a t saves time. To a n operator analyzing a certain t y p e of gas in routine work short cuts will suggest themselves. As a n illustration of t h e possibilities of this a p p a r a t u s for technical work, t h e following analyses of coal gas drawn from t h e mains of t h e city of Pittsburgh were made in a b o u t I hour each (Table 11): TABLE 11-ANALYSIS I I1
OF
Cc. cc. Taken for analysis.. , . 6 7 . 1 5 8 6 . 6 5 1 65 2.15 Absorbed K O H . . . . . Absorbed fuming HzSOa.. , , . , , , , , , , . 5 , 3 0 6.45 Absorbed pyrogallate 0 . 0 5 0 . 10 Contraction 26.00 3 3 . 6 0 COS producid Cue.' 8 . 4 0 10.90 Contraction ( Combus- 4 8 , 8 5 6 3 . 8 5 Con, 1 t i o n . . 2 5 . 7 5 34.30
1
PITTSBURGH COALGAS I 2.45 7.90
2.50 7 50
0 2 . . . . ., , .. . . . . 0.10 H*. . . , . . . . . , . . . . 3 8 . 8 0 CO . . . . . . _ ., . . . . 1 2 . 5 0 C,,H>, ,. - ..4 , 7 - . .. . , . 3 J . 70 N?.. , , . , . . . , . . 2.45
0.10 38.80 1 2 60 3 5 . YO 2.60
P e r cent COz., , . , , . , , . , , , Illuminants., . . . .
-.
I1
__
100.00 100.00
T h e average value of 11 in C n H Z n + 2 is about 1.08. H a d one complete combustion been made a f t e r reSee the gas analysis manuals of either Dennis o r Hempel. Burrell and Seibert (loc. [if., p p , 80-86) have called attention t o the f a c t t h a t a correction for molecular volumes of carbon dioxide a n d ethane should be applied in calculating from combustion d a t a , but unless the concentration of hydrocarbons is great, the correction will be small. 3 J o v r . F r a n k . I n s t . . Sept., 1898. See also Porter a n d Ovitz, Bureau ormnes,Buii. I , ~ . Z ~ . 1
1
848
T H E J O U R N A L OF I N D U S T R I A L A N D ENG1,VEERING CIfE.WISTRZ'
moval of CO by absorption, which is t h e usual technical practice, a n d t h e d a t a calculated t o C H I a n d Hz, we should have obtained 3 6 . 0 per cent H, instead of 3 8 . 8 cer cent, a n d of hydrocarbons 3 8 . 5 per cent instead of 3 5 . 7 cer cent. SUMMARY
A gas analysis apparatus combining several old principles has been described, which is n o t only adapted t o research, where precision in gas analysis is required, b u t i s recommended for technical laboratories as a n instrument of wide application, securing accuracy without much sacrifice of speed. A convenient a n d accurate method for t h e separation of t h e combustible gases, C O , H2, CH,, CzHe, etc., is given. The number of liquid absorbents t h a t may bc used is unlimited, hence very complex gas mixtures may be analyzed. This apparatus, in daily use in this laboratory for six months, has given complete satisfaction. Ex~anmanh r ~s~ ~ I s. A B O R ~ O ~ V BUREAU os MINSS, Prmauvow
THE INSTANTANEOUS THERMOSTAT AND SMOKE AND FUME MONITORS, PRECIPITATORS AND RECORDERS By W. W. STMNC Received Jirne 30. 1914
One of t h e most important developments in t h e progress of physics a n d chemistry in t h e past century has been t h e development of t h e subject of ionization. I n contrast t o atoms a n d molecules, ions are particles possessing a very short life and during their existence they undoubtodly experiencc many changes in t h e size of their electrical charge a n d t h e number of molecules t h a t go t o make. u p t h e ion cluster. I t is from t h e temporary character of ions t h a t t h e following instruments derive most of their utility: In engineering work of a chemical nature many processes are accompanied by intense ionization a n d among these one of t h e m o s t prominent is t h a t of t h e metallurgical furnace. The high temperature a n d t h e chemical reactions taking place in these furnaces are invariably accompanied by intense ionization which m a y include t h e emission of electrons by t h e hot surfaces, the emission of thermions, t h e recontbinalion of ions, t h e clustering of molecules and ions, the diffusion of ions, a n d t.he other ionic phenomena t h a t have recently been investigated by scientists. A N INSTANTANEOUS
,
TIIERXOSTAT
The sluggishness of t h e ordinary mercury or gas thermometer, t h e thermopile, t h e electric resistance thermometer, a n d other temperature recording instruments is well known. This sluggishness is due in p a r t t o t h e thermal element being covered, a n d i n p a r t t o t h e thermal capacity of t h e instrument itself. When t h e temperature of a gas is t o be measured t h e thermal capacity of t h e thermometer may play a very considerable role in causing a considerable time t o elapse for a n equilibrium of temperature t o take place. I n many cases t h e intensity of t h e ionization i n a gas may be a more or less known function of t h e temperature of t h e gas, due regard being given t o t h e life history of t h e ions in t h e gas. Let us assume t h a t
Val. 6 , No.
10
little or no dust or fumes is present in the gases and t h a t the gases are subjected t o a n intermittent flame. Under these conditions t h e pas will also be subject t o a n intermittent ionization and this will give i t a n intermittent conductivity. I n m y instantaneous thermostat 1 use a piece of apparatus similar t o my f u m e a n d smoke monitor (described in t h e latter part of this article) which contains two electrodes disposed within t h e gas. The thermostat is made to respond t o variations i n t h e conductivity of t h e gas in t h i s gap--the conductivity being high when there is flame or high temperature a n d low when there is little or no flame or low temperature. As there is no thermal conductivity or capacity involved in this indicating thermostat, i t i s seen t h a t its action is practically instantaneous. I t will be recognized immediately t h a t t h e relation between t h e ionization and t h e temperature would have t o be known before this t y p e of instantaneous thermost?.t could be used t o indicate absolute temperatures. There are many commercial conditions, however, where absolnte temperatures are not required. T N E S M O K E A N D FUME MONITOR
When t h e gases from furnaces contain fumes, dust
or smoke particles, i t is found t h a t the ions combine with these particles and lose their charge.
In this way
Fzc. I
t h e conductivity of t h e furnace gases is greatly diminished a n d this decrease in conductivity can be utilized t o indicate the density of t h e fumes, dust or smoke. I n many cities ordinances prohibit the emission of coal smoke exceeding a certain density a n d t h e above principle can be used a s t h e basis of a n apparatus f o r indicating when a smoke stack is violating the city ordinance. Fig. 1 is a photograph of a smoke monitor of t h i s type. I t is designed to give a n instantaneous indication when a stack is disobeying t h e city ordinance by ringing a bell (an alternating current bell such as B) a n d by illuminating certain directions which should be followed by t h e furnace operator. These directions may be anything t h a t will result in t h e most efficient and smokeless operation of t h e furnace. In t h e figure t h e directions apply t o a hand-fired furnace a n d are:
