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T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
value of this material as a fertilizer still seems t o be a n open question, many agronomists and agricultural chemists strongly recommend its use, supporting their recommendations by considerable data obtained by actual plot tests. I n 1912 t h e annual consumption of raw ground phosphate rock, based on t h e amount marketed, was 48,365 tons. While this is less t h a n 1.29per cent of t h e total phosphate produced and only 4.01 per cent of t h a t marketed in the United States, t h e sale of ground rock is becoming quite a factor in t h e phosphate industry. BUREAU O F SOILS, WASHINGTON
DETERMINATION OF CARBON I N STEEL AND IRON BY THE BARIUM CARBONATE TITRATION METHOD' By J. R. CAIN
The disadvantages attending t h e use of weighed absorption tubes as means for accurately determining carbon dioxide obtained during the combustion of steels and irons are in part as follows: 1-The elaborate precautions required t o prevent change of weight of t h e tube due t o gain or loss of moisture, necessitating complications in the purifying train before and after t h e furnace and t h e use throughout t h e apparatus of drying agents of t h e same hygroscopic power. 2-Difficulties in weighing large glass vessels caused b y electrical effects in wiping, b y buoyancy and b y changes in temperature between balance room and laboratory. 3-The necessity for maintaining constant conditions with respect t o t h e atmosphere within the tube, requiring sometimes a long period of aspiration after the combustion is completed. 4-The liability t o error from access of gases containing sulfur and chlorine, which may be formed during combustion of t h e metal or of t h e carbonaceous residue therefrom. 5-The difficulty of determining whether the increase in weight of t h e tube is due solely t o carbon dioxide. 6-The time lost in waiting for absorption tubes t o reach a condition of equilibrium before weighing. Those who have used absorption tubes for work requiring a high degree of accuracy know t h a t neglect of one or more of the precautions indicated above may easily occasion errors ranging from several tenths of a milligram t o one or more milligrams. It is evident, too, t h a t if t h e complicated purifying train used with an absorption tube gets out of order, or if t h e tube itself introduces error in some of t h e ways enumerated, it may often be a difficult matter t o locate and correct t h e trouble. It is not surprising, therefore, t h a t methods dispensing with t h e use of weighed potash bulbs, soda-lime tubes and the like are beginning t o be used extensively by steel analysis. Of such methods t h e weighing of the carbon dioxide in t h e form of barium carbonate precipitate directly or after conversion into have been much used, the 1 Published b y permission of t h e Director of t h e Bureau of Standards. Presented at t h e Cincinnati Meeting of t h e American Chemical Society April 6-10, 1914.
465
method abroad,l and the carbonate method in this country. Thus, of 6 2 prominent American laboratories (representing manufacturers, consumers and testing laboratories) 3 2 used t h e potash bulb, 24 weighed t h e carbon as barium carbonate, 3 titrated t h e excess of barium hydroxide, 2 used soda-lime tubes and one weighed an absorption tube filled with barium hydroxide.2 It is evident, in estimating the carbon dioxide by weighing the barium carbonate precipitate, or the sulfate obtained from it, t h a t the difficulties mentioned above as peculiar t o weighed absorption tubes, except number four, are eliminated or minimized; access of sulfur trioxide would still tend t o cause high r e s ~ l t s . ~If, however, the barium carbonate is measured b y filtering i t off and titrating it against standard acid, due regard being had t o proper conditions for filtration and washing, there is no likelihood of error from any of t h e causes enumerated. The principle of this method is described in most standard text-books on quantitative and volumetric analysis, b u t there seems t o have been but little application in steel analysis. The purpose of this paper is t o show the special suitability of this procedure for accurate and fairly rapid steel analysis, taking up in order t h e sources of error or difficulty and t h e means of avoiding or minimizing these, and finally giving t h e results obtained b y a series of analyses of pure sugar and of Bureau of Standards analyzed irons and steels. Without further consideration it can be seen t h a t t h e adoption of this method a t once simplifies t h e purifying train required after the furnace; nothing a t all likely t o be present in t h e escaping gases can affect the results if we except finely divided oxides carried over mechanically as the result of a very violent combustion. N o such oxides were noticed during this work or during the analyses of many other samples by different methods; if there is any reason t o suspect their presence, a simple filter macle by filling a U-tube with 20-mesh quartz, previously carefully washed with hydrochloric acid and water. will remove them. The points involving sources of error which were investigated were: (I) completeness of absorption of the carbon dioxide, ( 2 ) amount of washing necessary t o remove the excess of barium hydroxide, (3) solubility of barium carbonate in the wash water, (4) exclusion of extraneous alkaline substances. I n addition there were devised ( 5 ) means for t h e rapid filtration and washing of the barium carbonate with exclusion of carbon dioxide from the air. I-COMPLETEKESS O F ABSORPTIOS-This was established b y burning sugar in amounts giving approximately t h e weights of carbon dioxide obtained during steel analysis, comparing the percentages of carbon obtained with the theoretical. As a further check two 8-bulb Meyer tubes (shown in size in Fig. I ) 1 Bauer and Deiss, Probenahme und Analyse t o n Eisen und Slahl, 1912, p. 121. 2 D a t a communicated t o t h e author a s member of a technical committee
On 3 There is b u t little likelihood of SOz being produced in burning steel a n d iron. A n y small amounts of BaSOs resulting thereby would be removed by washing (see Sec. 5 on Filtration a n d Washing), t h e solubility of Bas02 being approximately 0.02 gram per 100 cc. of water a t 20' (Seidell, "Solubilities of Inorganic a n d Organic Substances," 1907).
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
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were worked in series. So long as a moderate rate of bubbling was maintained no cloudiness was ever observed in t h e second tube. I n this connection, McCoy and Tashiro' have shown t h a t 1.0 X 1od7 grams of CO2 can be recognized as a turbidity. If, however, t h e oxygen is passed too rapidly, particularly when burning steels containing more than I per cent carbon, some COz may reach the second tube. The proper rate of gas current t o retain all the COz in t h e first tube is easily established b y t h e operator after a few trials. 2-AMOUNT OF W A S H I N G NECESSARY-Barium carbonate itself reacts alkaline t o phenolphthalein, consequently this indicator cannot be used t o show when all of t h e barium hydroxide has been removed. The practical question as t o how much washing was necessary was decided b y washing the barium carbonate obtained from t h e combustion of accurately weighed amounts of sugar until results agreeing with t h e theoretical, within a small experimental limit, were obtained. The amount of wash water thus determined Was increased by 2 j per Cent. About I j0 cc. wash water were usually found sufficient. The results are summarized in t h e recommendations later, under t h e head "Filtration and Washing of the Barium Carbonate." 3-SOLUBILITY O F BARIUM CARBONATE I N WASH WATER-The possible effect of the slight hydrolysis of t h e barium carbonate in causing low results b y solvent action of the wash water was studied by comparing t h e results obtained when determining the barium carbonate from the combustion of the same weights of sugar, first by washing as above described, and then with twice and three times the amount of water recommended. The results showed t h a t the error from hydrolysis is negligible for present purposes. (See table and footnotes c and d , p. 467.) Holleman2 found the solubility of freshly precipitated B a C 0 3 in COz-free water t o be I part BaC03 in 64,070 parts water a t 8.8" and I part in 45,566 Parts water a t 24.2", or approximately 1 part in 50,000 a t the ternperature of the laboratory during this work, i. e., 20' t o 2 2 ' . On this basis I j o CC. wash water (See preceding section) would dissolve about 0.0003 gram BaC03 = o.oooo18 gram carbon. This be negligible for present purposes, and t h e amount disbe less than this because Of the repression of solubility during the first washings by t h e barium hydroxide still present; also i t is quite possible t h a t in the rapid Passage through the filter there has not been sufficient time for t h e wash water t o become saturated with barium carbonate. Holleman's results are in good agreement with those of Binea~.~ Holleman called attention to the fact, also recorded by Bineau, t h a t the Presence of carbon dioxide in water appreciably raises the solubility of barium carbonate and Holleman explains in this way the solubility of I part in 14,137 parts of water observed by Fresenius, who left the carbonate in contact with water exposed t o the air for several days. 1 2
Orig. Communication, 8th I n l . Congr. ApP1. Chem.. 1 (1912). 361. 2. p h y s i k . Chem., 12 (1893). 135.
3
Ann. chim. p h y s . , [3]E l , 290.
P POSSIBLE
SOURCES
OF
Vol. 6, N o . 6
EXTRANEOUS
ALKALINE
suBsTANcEs-These are: ( a ) substances derived by action of water on the bottles containing the C02-free water mentioned later; such action should be avoided by choosing a good quality of glass bottle; Jena glass containers were found satisfactory; ( b ) alkali carried over mechanically from soda-lime guard-tubes by the air used to force out Con-free water; thick plugs of glass wool will remove this source of danger; (c) action of barium hydroxide on the walls of the ICleyer tubes; these tubes should not give up alkaline substances t o the standard acid after barium hydroxide has stood in them for l/z hour and t h e tubes have then been thoroughly washed with alkali-free water; ( d ) action of barium hydroxide on filtering material; glass wool as a filling material is absolutely excluded on this ground; quartz has been found very satisfactory (see description of filtering apparatus) ; amphibole asbestos for the felt was found suitable from this standpoint as well as because of its resistance t o attack by N / I O hydrochloric acid. j-FILTRATION A X D W A S H I S G O F T H E B A R I U M CARBONATE-This is carried out with the apparatus shown in the figure. The cut is approximately one-tenth size
APPARATUS FOR FILTERING BARIUM CARBONATE
FIG.I
and is self-explanatory. S is a two-way stopcock connected to the suction pipe. The rubber tubing connected t o the A)Teyer tube should be of best grade black rubber, and the lengths used should be chosen so as to permit of easy manipulation of the tube. The Meyer tube is connected or disconnected by the rubber stoppers which are eft always attached t o t h e rubber tubes. The carbon filter C is fitted with a perforated porcelain plate, sliding easily. The funnel is prepared for filtrations by making a felt of asbestos on the porcelain disc, using asbestos which has been digested for several hours with strong hydrochloric acid and then washed free of acid. on top of t h e asbestos is a layer of similarly washed quartz of of
the height shown in the figure. A mixture of grains various sizes (approximately j o per cent passing
a ao-mesh and t h e remainder passing a ro-mesh and remaining on a 20-mesh sieve) is suitable. A mixture of quartz and asbestos works well and may be simply obtained by filling t h e funnel with a suspension Of asbestos and delivering t h e quartz t o the funnel from a beaker by means of a strong jet of waterf r o m the wash bottle, while maintaining a gentle suction. I n this way the asbestos is properly mixed with the
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quartz. Proper, attention t o these details will be found to greatly expedite filtration. The stopper is now inserted in t h e funnel, t h e Lleyer t u b e connected as shown, and t h e liquid and precipitate sucked into t h e funnel. Only very gentle suction should be used. When necessary, P3 is opened t o admit air back of t h e column of liquid in t h e Meyer tube. When t h e contents of t h e tube have all been transferred, t h e large bulb nearest B is half-filled with water b y opening P I ; t h e stopcock S is operated during this and subsequent operations so as t o maintain a gentle suction. M is now manipulated so as t o bring t h e wash water in contact with all parts of t h e interior, after which the water is sucked out through C ; P2 is left open during this and subsequent washings. After eight washings, as directed, allowing t h e wash water t o drain off thoroughly each time before adding more, M may be detached, t h e stopper removed from t h e funnel and t h e washing completed b y filling C t o t h e t o p with COz-free water, sucking off completely and repeating t h e operation once. Air is now admitted through the side opening of S , C is removed and t h e porcelain disc carrying t h e quartz asbestos and barium carbonate is shoved, b y means of a long glass rod, into t h e flask used for titrations, removing from t h e sides of C any adhering particles b y a jet of water from the wash bottle. APPARATUS F O R COMBUSTION
APPARATUS-The method requires no modification of a n y of the accepted appliances for t h e combustion of iron and steel. I n the present work both gas and electrically heated furnaces were used. As already stated, there was no purifying train after the furnace, t h e Meyer tube being directly attached. Before t h e furnace was a n electrically heated porcelain tube filled with copper oxide; then a calcium chloride tower filled with stick potassium hydroxide. Steels and irons were burned on a bed of alkali- and carbon-free alundum contained in a platinum boat. The blanks obtained by carrying through a complete determination, including filtration, washing, etc., but with omission of any carbon-containing substance, were usually 0.0 cc. and never more t h a n 0.05 cc. of N / I O hydrochloric acid, showing not only t h a t t h e oxygen was sufficiently purified and t h e apparatus in good condition, b u t t h a t t h e operations of filtration, washing, etc., introduced no appreciable positive error. SOLUTIONS USED
TENTH-NORMAL HYDROCHLORIC ACID-standardized by any of t h e accepted methods, or as follows: 2 0 cc. of t h e approximately N / I O acid are measured out with a pipette, 5 cc. of nitric acid ( I t o I by volume) added, and t h e silver chloride precipitated by a n excess of silver nitrate solution in a volume of j o t o 6 0 cc. After digesting a t 70' t o So" until the supernatant liquid is clear, the chloride is filtered off on a tared Gooch filter and washed with water containing 2 cc. of nitric acid per I O O cc. of water until freed from silver. After drying t o constant weight a t 130°, the increase of weight over t h e original tare is noted and t h e strength of t h e hydrochloric acid calculated on the basis of t h e weight of silver chloride t h u s ob-
467
tained, afterwards adjusting t o t h e strength prescribed. Several concordant determinations with varying amounts of acid should be made. I cc. N / I O HC1 = 0.0006 gram carbon. T E N T H - N 0R M A L
S 0D I U M
H Y D R 0X I D E
S 0 L U T I 0 hT-
Standardized against t h e hydrochloric acid solution, with methyl orange as indicator. This solution is conveniently stored in a large glass bottle fitted with a soda-lime guard tube and arranged for delivering t h e solution by air pressure. METHYL ORANGE-0.02 gram dissolved in IOO cc. of hot water and filtered. BARIUM HYDROXIDE SOLUTION-A saturated solution filtered and stored in a large reservoir from which i t is delivered by air pressure, protecting from carbon dioxide by a soda-lime tube. Three or four small bulbs of t h e Meyer tube are filled, and Con-free water is added until t h e remaining small bulbs are filled. When burning products high in carbon t h e stock solution may be used undiluted. C A R B O N D I O X I D E - F R E E WATER-This iS Conveniently made by passing air for a sufficient length of time through a soda-lime tube and into a 6- or 8-liter bottle filled with pure distilled water. The water is delivered b y Con-freeair under pressure. THE M E T H O D
The combustion is carried out in the usual manner, care being taken not t o pass the oxygen too rapidly. After filtering, washing and transferring t h e contents of t h e filter t o a flask, as described under "Filtration and Washing of t h e Barium Carbonate," a slight excess of the standard acid is added from a burette, using a portion t o rinse out the Sleyer tube, and the excess of acid is then titrated against the sodium hydroxide, using methyl orange as indicator. RESULTSOBTAINEDBY BARIUMCARBONATE TITRATION METHOD Carbon Carbon found Difference Weight present Gram Gram Gram Gram Material Sugar(a) ..................... 0.0100 0,00421 O.O042i(c) +0.00006 0.00420 -0.00001 0.0100 0.00421 0.00430 +O.OOOlO 0,0100 0.00421 0.00840 -0.00002 0.0200 0.00842 0.00860 +0.00018 0.0200 0.00842 0.00860 +0.00018 0.0200 0.00842 0.01280 +O.OOOli 0.0300 0.01263 0.01280 +0.00017 0.0300 '0.01263 0 . 0 1 275 ( d ) + O . 00012 0.0300 0 . 0 1 263 Bessemer Steel B. S No. 23.. . 1.000 0 . 0 0 8 0 5 ( b ) 0.00805 0.0000 1,000 0.00805 0.00805 0.0000 1.000 0.00895 0.00805 0.0000 0 . 0 0 8 0 0 ( c ) -0.00005 O.O03?3(b) 0,00372 -0.00001 B e s s e m e r S t e e l , B . S . , N o . l o b . . 1:OOO 1,000 0.00373 0.00372 -0.00001 Pig Iron C , B. S., No. 5 b . . ...... 1.000 0.02726(b) 0,02710 -0.00016 1.000 0.02726 0.02710 -0.00016
.
Mean error, sugar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $0.000094 -0.000056 Mean error, steels and i r o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . (a) B. S. Standard Sample N o . 1 7 . A 1 % aqueous solution was made and the required amounts were delivered into a porcelain boat from a burette. After careful evaporation of the water the sample was burned. ( b ) Certificate values. (c) Washed with double the usual amount of wash water. T h e second portion of wash water was titrated against the N/lO hydrochloric a u d ; the amounts used a f t e r deducting the blank when titrating the same quantity of t h e water used for washing were 0.10 cc. and 0.15 cc. ( d ) Washed with three times the usual amount of wash water.
The results given in t h e table show t h a t t h e method is as accurate as t h e weighing methods. It is not so subject t o disturbing influences and requires less elaborate apparatus t h a n those methods do. S O T E S AND PRECAUTIONS
I-After a little practice a precipitate can be filtered and prepared for titration in five minutes.
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a-When working with steels high in carbon (above i t is advisable not t o use more t h a n one gram, in order t h a t filtration may be sufficiently rapid. 3-For very accurate work the Meyer tubes should be washed with dilute acid before beginning work each day. .After a determination is finished, the Meyer tube should be completely filled two or three times with t a p water, then rinsed with distilled water, in order t o remove t h e carbon dioxide liberated when dissolving the carbonate from t h e previous determination. 4-The flask containing t h e carbonate should be very thoroughly agitated after adding the acid. since the carbonate sometimes dissolves rather slowly if this is not done; this is particularly the case if i t has packed much during filtration. j-The rubber tube connecting B (see figure) t o t h e hleyer tube should be washed with a little water from B , before beginning determinations each day. I a m indebted t o Mr. H. L. Cleaves of this Bureau who prepared the drawing of t h e filtering apparatus and made many determinations on steels which will appear in a later publication. 1%)
BUREAUOF STANDARDS WASHINGTON
THE DETERMINATION OF AMMONIA IN ILLUMINATING G A S By J. D . EDWARDS Received March 21, 1914
This paper is a summary of t h e results of a brief investigation of t h e apparatus and methods employed for t h e commercial determination of ammonia in illuminating gas, A fuller report will. be found in Bureau of Standards’ Technologic P a p e r No. 34, and t h e application of this work in the form of operating directions for carrying out the determination will be included in Bureau of Standards’ C i r c u l a r No. 48, “ S t a n d a r d Methods of Gas Testing.” The method generally used for t h e determination of ammonia in purified illuminating gas depends upon t h e absorption of t h e ammonia in a standard acid solution, the amount of ammonia absorbed from a measured volume of gas being determined either by titration of t h e acid remaining unneut’ralized, or less frequently b y allowing t h e gas t o pass until t h e change in the indicator used shows t h a t all t h e acid has been neutralized. The choice of t h e proper indicator t o use for this determination is of greater importance t h a n t h e choice of apparatus, since t h e use of an unsuitable indicator may introduce large errors, amounting in extreme cases t o more t h a n one hundred per cent. Many indicators have been and still are commonly used which are not a t all suited t o t h e purpose, failing t o meet one or more of t h e following essential requirements: I-It should show a sharp end point in dilute solutions. 2-It should be sensitive t o ammonia and not be seriously affected by ammonium salts. 3-The end point should be affected as little as possible by carbon dioxide. Abstract 1 Published by permission of Director, Bureau of Standards. of paper presented at the Cincinnati Meeting of the American Chemical Society, April 6-10, 1914.
Vol. 6, No. 6
The indicators which were found t o be most suitable for t h e determination of ammonia in gas were sodium alizarinsulfonate, cochineal and paranitrophenol. Sodium alizarinsulfonate is less sensitive t o carbon dioxide t h a n either cochineal or paranitrophenol and gives a color change from greenish yellow t o brown which is quite sharp even with very dilute solutions. Sodium alizarinsulfonate was t h e indicator used in t h e remaining experimental work. Methyl orange, though less sensitive t o carbon dioxide t h a n the above indicators, does not give sufficiently sharp color changes with weak solutions. Phenolphthalein and litmus, of course, are too sensitive t o carbon dioxide t o be of use here. The presence of glass beads which are used in some of the absorption apparatus may lead t o erroneous results for two reasons: ( I ) The beads may yield alkali on contact with t h e absorbing liquid; ( 2 ) washing of t h e beads may be incomplete. Although t h e absolute amount of alkali which might be dissolved from t h e beads is small, it may be equivalent t o a considerable percentage of the total amount of ammonia t o be absorbed. For this reason, i t is recommended t h a t the operator test the solubility of a n y beads he may use. The method of washing out t h e apparatus should also be tested t o insure complete washing with a minimum of wash water. Five different forms of apparatus were tested: The Referees apparatus, t h e Emmerling tower, t h e Lacey apparatus, t h e common form of gas wash bottle and a modified form of t h e Cumming wash bottle. This latter form (Fig. I ) was designed a t t h e Bureau
H
>{
FIG. ~-MODIPIED CUMMING WASHBOTTLE(ONE-FOURTH SIZE)
of Standards fqr this work. I n this form, t h e gas passing through t h e small nozzle acts like an injector and circulates t h e liquid rapidly and continuously, thus bringing fresh acid into contact with t h e gas. T h e relative efficiency and from this the probable accuracy of the different forms of apparatus was determined by running the different forms in parallel, using gas from a common supply. A R / j o solution of sulfuric acid was used as t h e absorbing agent. It was not considered desirable t o use a stronger solution t h a n this because of t h e small amount of ammonia t o be absorbed and t h e fact t h a t small errors in t h e measurement of stronger solutions make a large error in t h e ammonia apparently absorbed. As a result of this comparison it was found t h a t the Emmerling tower gave results which were somewhat higher t h a n those obtained with t h e other forms and t h a t the wash bottle gave results consistently lower.
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