Oct., 1919
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were too high was correct. R . J. Young and J. S. Stauffer used only the modified method. Canby Method Per cent As Rowley ..................... 24.92 Stauffer.. . . . . . . . . . . . . . . . . . . .24.39 Young ...................... 24.55
Bennett Method Per cent As
{ ;:: ;; 24.90 25.02
With the single exception mentioned, none of the students had attempted the analysis before and in the case of all it was part of their prescribed course. None of them was able t o spend enough time to carry out a complete research; but t o all, the difficulties were explained and the object t o be attained was pointed out and they carried out their analyses with the aim and in the spirit of research. Two other students, H. C. Boehmer and I. L. Sills, did some pioneer work over a year ago, chiefly in varying tests of Canby’s method, and though their results are not included in this paper, their work was as important as t h a t of the others. I may add t h a t in work like this, I think it is possible for students in the second year of their analytical course t o get some insight into the methods of research which will help them towards the initiative and judgment so much desired by the industries employing university students and graduates. SUMMARY
I-Bennett’s modification of Pearce’s method for arsenic, if carried out as he describes, is likely t o give too high results, unless arsenic has been lost by volatilization or otherwise, while Canby’s modification, if carried out as he describes, may be so low as t o be valueless. 11-Both methods may be modified t o give practically concordant results; and if duplicates, determined one by the Bennett method and the other by the Canby method, each modified as described, agree, then the result may be considered correct. 111-In the modification of Bennett’s method, any large amount of alkali is acidified with nitric acid, made slightly alkaline with pure caustic soda and very slightly acid with acetic acid, before precipitation of the arsenate as silver arsenate. In the modification of the Canby method the process is similar, except t h a t instead of acetic acid, nitric acid is added in very slight excess and, after addition of silver nitrate, this small excess -is neutralized by zinc oxide. IV-Various determinations are given illustrating the degree of accuracy. CHEMISTRY DEPARTMENT QTJSSN’S UNIVERSITY KINGSTON, ONTARIO
AN IMPROVED METHOD FOR DETERMINATION OF CARBON BY WET COMBUSTION, USING BARIUM HYDROXIDE AS ABSORBENT By P. 3,. HIBBARD Received March 10, 1919
For the determination of carbon by wet combustion, the writer has for more than a year used a modification and combination of previously published
941
m e t h o d s 1 ~ 2 ~ 3with > 4 ~ 6much success. The method is simple, convenient, inexpensive, rapid, and accurate. It is here presented, with the hope t h a t it may be of use t o others. Complete combustion is secured by suitable proportion and quantity of reagents. Carrying over of volatile acid fumes t o the absorbent is avoided by an efficient purifying train. Convenience and accuracy in use of barium hydroxide as absorbent for carbon dioxide are secured by a simple and efficient apparatus without difficult manipulation. The operation is briefly as follows: The substance is heated in a Kjeldahl flask with chromic anhydride and sulfuric acid whereby carbon is oxidized t o carbon dioxide which is carried into a solution of barium hydroxide by a current of purified air. After the reaction is completed the excess of barium hydroxide is determined by titration with standard hydrochloric acid. The amount of barium hydroxide neutralized by carbon dioxide measures the amount of carbon in the substance taken. DESCRIPTION O F APPARATUS
By reference t o Fig. I the various parts and arrangement of the apparatus may readily be discovered. First is a bubble tube A, containing a few drops of colored liquid as indicator of t h e speed of t h e air current. B is a large test tube filled with soda lime for purifying the incoming air. C is the regulating stopcock; D is a funnel tube with a long stem extending down t o the bulb of the Kjeldahl flask F. The end of this long stem is somewhat drawn out t o a small opening. Upon D, connected by a two-hole rubber stopper rests E, a graduated dropping funnel for measuring the reagents. F is a long neck, 300 cc. Kjeldahl flask, used for the combustion chamber. From this the gas passes through a glass tube t o the bottom of G, a large test tube drawn out a t the lower end and fitted with a pinchcock and rubber tube. This acts as the condenser t o remove most of the water from the gas. After each combustion is finished the water is drained out of this tube b y opening the pinchcock. From G the gas passes through a long tube down t o H, a 5 0 cc., wide-mouth flask containing about I O cc. of strong sulfuric acid. Upon H, which is fitted with a two-hole rubber stopper, rests a glass tube, I, filled with glass beads wet with sulfuric acid, t h e purpose of which is t o dry the gas. Upon I, connected by a rubber stopper, rests J , a similar tube filled with granulated amalgamated zinc, the function of which is t o remove sulfuric acid or other acid fumes from the gas. From the purifying tube J the gas passes through a long tube down t o the 500 cc. Florence flask K, which is connected by a two-hole rubber stopper t o the Meyer bulb tube L. The lower end of this bulb tube is bent so as t o almost touch the bottom of the flask. At t h e upper end the bend next t o t h e large bulb is partly straightened out so t h a t the bulb stands upright. Ames and Gaither, THISJOURNAL, 8 (1916), 1126. a Truog, I b i d . , 1 (1915), 1045. Schollenberger, I b i d . , 4 (1912), 436. 4 Gortner, Soil Science, 2 (1916), 395. 6 Brady, THIS JOURNAL, 6 (1914), 843. 1
*
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942
This Meyer bulb tube stands a t an angle of about 30' with the horizontal. Above the large bulb of t h e Meyer tube, connected by a rubber stopper, is a small bulb, M, used as a safety t r a p t o prevent carrying over any of the liquid. This bulb M is connected with the suction by N. The suction apparatus may be any form of aspirator or vacuum pump which gives a vacuum equal t o about 2 in. of mercury. I use a pressure regulator consisting of a narrow cylinder containing mercury and fitted with a three-hole rubber stopper. One hole is for the connection t o the Meyer bulb, one is for the connection t o the suction, the other carries a straight glass tube extending about 2 in. below the surface of t h e mercury. This regulates t h e vacuum so that if there is more thanenough t o raise a column of 2 in. of mercury it is relieved by air passing in through this open tube.
Vol.
11,
No.
IO
found in preventing the passage of acid fumes from the digestion flask into t h e absorbent liquid is perfectly overcome b y means of the bead tower with sulfuric acid followed b y the tube of granulated zinc. It was found t h a t it was necessary t o keep the zinc d r y in order t o secure efficient working. T H E C O N T A I N E R F O R BARIUM H Y D R A T E
This consists of a large bottle fitted with a good sized soda-lime tube for purifying all the air t h a t enters t h e apparatus. The barium hydroxide is drawn off and measured by means of a jo cc. automatic overflow pipette. The upper end of this pipette is connected back into the top of the bottle so t h a t only air which has passed through the soda lime can enter it. By this means the barium hydroxide ,may be readily measured out in exact amount and preserved indefinitely from contamination b y the air. D E S C R I P T I O N O F T H E METHOD
J
> I
FIG. I
The whole of the purifying apparatus and the combustion flask are carried on a single, ordinary ring stand. The absorption flask, which may be either a Florence flask or a n Erlenmeyer, in an inclined position rests on the table and supports one end of the Meyer bulb tube, the other end of whichis supported by asmall ring stand. The above described combustion apparatus comprises a single unit. If i t is desired t o use more than one the primary purifying train and suction apparatus may be used in common for all of them and i t will be easily possible for one person t o handle half a dozen units like this a t once. I t has been found t h a t this absorption apparatus is more easily handled, more easily washed out, and works better than Truog's ingenious bead tower? The difficulties which previous experimenters have
' Loc
cit.
I n the combustion flask place the substance which may contain from 0.10 t o 0.15 g. of carbon, for example 0.3 g. of sugar, or I O g. of soil; connect up with the purifying apparatus. I n the 500 cc. Florence flask place I O O cc. of N / 3 barium hydroxide and 50 to 60 cc. of carbon dioxide-free water. The amount of water added should be such t h a t the barium hydroxide will rise only into t h e lower part of the large, upper bulb of the Meyer tube when the suction is in operation. This may also be partly regulated by raising or lowering the absorption flask K on the lower end of the Meyer tube. Connect up and turn on the suction so t h a t carbon dioxide-free air passes a t t h e rate of 150 t o 2 0 0 cc. per min. Place 1 5 cc. of chromic acid solution in the dropping funnel E over the combustion flask and run i t into t h e combustion flask. If the s u b stance t o be burned is readily decomposed the chromic acid must be added slowly in order to avoid a too violent reaction with consequent back pressure, causing low results. Now add 45 t o 50 cc. strong sulfuric acid t o the dropping funnel and run i t cautiously into the combustion flask t o avoid too violent reaction. During this time the current of air should pass regularly with no back pressure. After the reagents are added heat gently with a small flame until the acid boils. Continue boiling about 1 5 min. or until the mixture humps. The whole time should be 2 5 or 30 min. The reaction is probably complete as soon as the acid boils, but the rest of t h e time is allowed t o sweep all of the carbon dioxide into the absorption vessel. When completed, remove the heat, shut off the suction, disconnect t h e absorption tube and flask, and rinse out the barium hydroxide from the Meyer tube into the absorption flask with carbon dioxide-free water, using about 2 0 0 cc. Stopper the flask and set i t aside. The apparatus is now ready t o start another combustion, as a t first, by substituting a new evolution flask and a freshly charged absorption flask. When this has been properly started i t requires no attention for about 2 0 min. A t any convenient time the final titration may be made, or one may wait until ready t o make a number of them a t once? Add t o t h e liquid in the absorption flask
' L O G . cit.
OCt., 1919
T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
4 drops of phenolphthalein solution, 0 . 2 per cent, and run in standard N / 3 hydrochloric acid until the pink color disappears. There is no means of knowing when the titration is nearly completed so t h a t it is necessary to proceed cautiously in order t o avoid adding too much acid. If this should happen it may be remedied by immediately adding one or two cc. of the standard barium hydroxide, then continuing with the acid carefully t o the end-point. A blank should be run for the same length of time and with all the reagents and the same amount of barium hydroxide. The amount of hydrochloric acid required for the determination subtracted from the amount required for the blank gives the amount equal t o the carbon dioxide formed: I cc. N / 3 acid = z mg. of carbon. APPLICABILITY O F THE METHOD
As t h e temperature in the reaction flask is t h a t of boiling sulfuric acid i t is obvious t h a t t h e method is not suited for the combustion of volatile substances. It does serve well for the determination of carbon in soils, manures, and agricultural products in general, such as grains, fodders, etc. PREPARATION O F REAGENTS
B A R I U M HYDROXIDE-This is approximately N / 3 . If the solution is much stronger t h a n this i t is a p t t o
crystallize out when it gets cold. S T A N D A R D HYDROCHLORIC AcID-This iS N / 3 , standardized by any convenient method. I cc. is equivalent t o 2 mg. of carbon. CHROMIC ACID-170 g. of chromic anhydride (CrOa) is dissolved in 3 0 0 cc. of water. Add 2 5 cc. of sulfuric acid anti boil gently for 15 min. t o remove any carbon t h a t might be present. Cool and make up t o 500 cc. SULFURIC ACID-ordinary c. P. concentrated acid, free from carbon. iS easily made C A R B O N D I O X I D E - F R E E WATER-This in quantity by bubbling air which has been freed of carbon dioxide by passing over soda lime or caustic potash, through the distilled water for a n hour or two. T o determine its freedom from carbon dioxide add a drop or two of phenolphthalein t o IOO cc. of the water, then add a drop of barium hydroxide and mix. The water should he strongly colored. A C C U R A C Y OF R E S U L T S
The accuracy of the results obtained may be tested by t h e combustion of substances of known composition. T h e following results were obtained: Urea. ........................... Sugar, 99.6 per cent pure., ......... Soil. ............................ CaCOn ...........................
PER CENTCARBON Theory Found 20.0 20.08 19.84 41.5 41.9 41.6 1.3iO 1.374 12:O 11.86 11.86
The strength of barium hydroxide used is such t h a t cc. equals about 2 mg. of carbon. As i t is possible t o duplicate results within 0.1 cc. this indicates t h a t the error would be 0 . 2 mg. of carbon. By using an absorption apparatus similar t o the Truog tower and with barium hydroxide of one-tenth the above strength and with some extra precautions, i t has been found possible t o determine accurately carbonate carbon in soils with an error of only one or two p. p. m. I
COMPARISON
W I T H THE
G R A V I M E T R I C METHOD
943 TJSING
SODA L I M E F O R ABSORPTION
The above described apparatus is somewhat simpler and more easily obtainable t h a n t h a t required for the gravimetric method and there is no difficulty due t o moisture which must be guarded against in the gravimetric determination. It seems probable t h a t a larger number of units of the volumetric apparatus could be operated by one person t h a n of the gravimetric apparatus. Furthermore it is probable t h a t the error of determination is less in using the volumetric apparatus. This is because the soda-lime absorption bulb is very heavy so t h a t small changes in weight are not readily detected except b y means of an extra good balance. On the other hand, in case but few determinations are t o be made i t will be simpler t o use the gravimetric method, as in this case there are fewer solutions t o be prepared, and fewer reagents are required. Consequently a few results would be more quickly obtained by this method. As t o errors of manipulation i t is largely a question of personal error as t o which method will prove more satisfactory. AGRICVLTWRAL EXPERIMENT STATION UNIVERSITY O F CALIFORNIA BERKELEY, CALI
THE DETERMINATION OF MIXTURES1
CHLORIDE IN GAS
By V. C. ALLISON AND M. H. MEIQHAN Received March 223, 1919
I n the chlorination of natural gas, some method of quickly and approximately determining the methyl chloride produced was necessary as a control over the operation. I n looking over the literature the only method which the authors found described for analyzing methyl chloride was t h a t of heating over soda lime.2 As it was desired t o analyze a great number of samples a day, the soda-lime method was far from satisfactory from the standpoint of rapidity. Considerable time was expended in investigating and developing various suggested methods of determining methyl chloride and part of our results appear in this paper. PHYSICAI. PROPERTIES O F METHYLCHLORIDEs The gas is colorless and burns with a bright flame, edged with green Vapor Density = 1.73 (calculated = 1.75) Specific Gravity = 0.9915 at -23.5’ C.. and 0.9523 at 0’ C. Soecific Volume = 50.8 Skubilities: 1 volume of water dissolves 5.03 volumes of methyl chloride at 7’ C. and 3.46 volumes at 20’ C. 1 volume of alcohol dissolves 35 volumes of methyl chloride 1 volume of glacial acetic acid dissolves 40 volumes of methyl chloride (the authors found a somewhat greater solubility in glacial acetic acid) Vapor Pressure‘ Temperature Atmospheres Deg. C. 0 2.48 4.11 15 6.50 30 CHEMICAL REACTIONS~ When passed through a red-hot tube it deposits carbon and yields hydrochloric acid, methane, ethylene, carbon monoxide, and naphthalene. M A T E R I A L USED
I n our chlorination apparatus the chloroform and carbon tetrachloride were removed by water scrubbers, Published by permission of the Director of the Bureau of Mines. Watts’ “Dictionary of Chemistry.” Ibid. 4 Thorpe’s “Dictionary of Applied Chemistry.” 6 A , Perrot, Technical Paper 101, 375. 1 2
