Microdetermination of Organic Carbon by the Wet Method ED. F. DEGERIh-G A ~ I T. I Z. BALL Purdue Lniversity, Lafayette, Ind.
D
URISG the last few years, several simplified niet~liodr
Reagent
of determining carbon in organic compounds have been described in the literature. Their aim has been to offer a faster and more easily manipulated method t h a n the classical one of Liebig. Most of these methods involve oxidation of the sample with chromic anhydride and sulfuric acid. T h e evolved carbon dioxide is then measured by the increase in weight of a solid absorbent (8); b y absorption iii standard alkali, followed by titration (1, 3, 5 , 6); or by a11 increase i n pressure (due to t h e evolved carbon dioxide) in a closed system (e). Xone of these methods is particularly well suited for microwork. S e r n s t ('7) used the mercury bead dilatoiiieter t o ~iiea.jui'e sniall volume increases in vapor density determiiiati(ms by Victor Meyer's method. T h e dilatometer consists of a graduated horizont,al tube of sniall bore closed by a droplet of mercury which is free to move until t h e inside and outside pressures are equalized. T h e volume change is indicated b y the movement of the mercury along t h e graduated scale. Recently Clarke and Hermance (4) have applied this nietliod t o t h e determination of carbon dioxide in very m a l l samples of corrosion products. This apparatut. i5 especially well suited to certain niicromethoti~.
The oxidizing agent is composed of 0.1 gram of finely divided chromic anhydride suspended in 1.0 ml. of heated concentrated sulfuric acid (about 250" C.). This is niadr up in the desired quantity and kept in a glass-stoppered hott>le.
Procedure The capillary tube is cleaned with chromic-sulfuric acid mixture, rinsed with distilled water, and dried with a stream of dry air. The tube is calibrated by introducing mercury into it, noting the length of the mercury column, and then weighing the iiiercui'y. The reaction flask and weighing capsule are cleaned nith chromic-sulfuric acid mixture, rinsed with distilled watei and acetone, dried in the oven, and cooled in a desiccator. The sample (2.5 to 3.0 nig.) is weighed out and the xeighing capule ib alloivetl to slide down into one leg of the reaction flask. The ground joint is lubricated with a little stopcock grease, and the flask is attached to the buret. Rubber bands are the11 stretched over the lug;, to maintain ii constant tension on thc. joint. One milliliter of oxidizing mixture is introduced iiito the by means of a medicine dropper other leg of the reaction fl e mercury droplet is forced t(J the marked to deliver 1.0 nil. initial point by carefully aspirating air into the capillary. T h e stopper, lubricated with a drop of phosphoric acid, i;. inserted. The apparatus is allowed to stand for at least 10 minutes ill ordei to bring aliout tem , and i5 then tapped to aid iii bringing the position of rest. The position of the mercury is read, and the process is repeated a t short intervals until the position of the mercury remain? constant. The flask is heated to 85' C., allowed t u remain a t that temperature for 2 hours, and i j then cooled and the position of the mercury is read ah before.
kfi CAPSWr
fND
Calculations T h e volume of carbon dioxide is obtained from t h e difference in the positions of the mercury.
FIGURE I . DIAGRAM OF APPARATUS
22.4 nil. of carbon dioxide a t standard temperature and pressure 12 mg. of carbon
It occurred to t h e authors t h a t m c h a n apparatus might be applied t o the determination of carbon in organic compounds, provided a satisfactory oxidizing agent could be found.
(,c
of carbon
=
(Rp - R1) y x 12 S X 62.36
x
P
100 3-1
where R2 and R1 are the positions of the mercury in em. S is the weight of the sample P is the barometric pressure t is the temperature of the room y is the volume of the capillary in mi. per cni.
Apparatus The apparatus has two essential parts: the tn-o-leg reaction flask (right), and the gas measuring buret, (left, Figure 1). The buret is made of capillary tubing (3-mm. inside diameter and 8mm. outside diameter) 70 cm. long, so that it has a volume of about 5 ml. The open end is funnel-shaped to facilitate cleaning, while the other end bears a KO. 7 ground joint. The buret is mounted horizontally on a wooden panel just above a meter stick. The panel also has a small spirit level rigidly attached to it and one adjustable leg to permit leveling the buret. The reaction flask is constructed of 10-mm. Pyrex tubing. It has two legs, each with a capacitj- of slightly more than 1 ml., a ground-glass stopper, and a capillary 8 cm. in length terminating in the male member of a ground joint. Both ground joints bear small lugs to which are attached rubber bands or springs in order to maintain a constant tension on the joints during the manipulations. The weighing capsule is made of 7-mm. tubing, closed and flattened a t one end so that it xi11 stand upright on the balance pan. It should be thickened a t the bottom to give it suf€icient Teight so that i t will not float on the surface of the sulfuric acid.
TABLE I. RESULTS Carbon,
Compound
Theory
Benzoic acid Salicylic acid rn-Nitrobensoio acid
Carbon, Obtained
%
%
88.81 60.85 50.28
ti$. 8, 6 8 . 5
61.0, 60.9 49.5, 50.4
Acknowledgment The authors acknowledge suggestions made by Hal C. Huffman, graduate student of the Chemistry Department. 1124
ANALYTICAL EDITIOD;
FEBRUARY 15, 1940
Literature Cited ddams, ISD. ENG.CHEM.,rlnal. Ed., 6, 277 (1934). (2) Chalmers, Ihid., 4, 1 (1932). (3) Ibid.,4, 143 (1932). (4) Clarke and Hermance, Ibid., 9, 597 (1937). (5) Kirk and Williams, Ibid.,4, 403 (1932). (6) hlohlman and Williams, Ihid., 3, 119 (1931). (1)
125
Nernst, 2. Eleklrochem., 9, 622 (1903). (8) Pollard, ISD. EKQ.CHEM..Anal. Ed., 7, 77 (1935).
(7)
PRESENTED before t h e Division of AIicrochemistry a t the 94th Meeting of the American Chemical Society, Rochester, N. 'Y. Abstract of a portion of a thesis submitted t o the faculty of Purdue Un;versity by T. Z. Ball in partial fulfillment of t h e requirements for the 1RI.S. degree.
A Furnace for Micro-Carius Determination JULIUS A . KUCK
iND
JI.4URICE GRIFFEL, City College. College of the City of S e w - York, S e w York. 5. Y.
A
LTHOUGH the micro-Carius determination offers one outstanding advantage-great accuracy-it is often avoided h y professional analysts because i t is time-consuming. Siederl (private communication) has found i t possible to reduce to one hour the time required in heating the organic substance with nitric acid in t h e glass bomb in order to decompose it. However, the time required for the furnace t o reach t h e necessary 300" C. and to cool d o v n t o room teniperature still constitutes a drawback. Gas furnaces are unsuitable in crowded laboratories and give unequal heating. Commercially available electric furnaces are expensive. This article describes a simple, homemade furnace v h i c h heats u p to 250" C. in 15 minutes and cools down from 300' C. t o room temperature in the same time.
General Design The furnace (Figure 1) consists of three heating units: A , which is contained within tTyo concentric steel c\hnders, and B and C, the space between the two being filled Iyith Sil-0-Gel as a heat-insulating medium. The space between A and B is empty and is utilized for cooling the furnace by passing through it a stream of cold compressed air. The ends of B and C are sunk to a depth of 0 125 inch into properly channeled Tranqite plates, D
(0.25 inch thick), n-hich have three holes drilled through them as shovn in Figure 2, to accommodate the ends of A which lie flush with the outside surface. The dimensions of the steel cylinders are as follows: Cylinder
; C
Length Inches 12 11.75 11.75
Outer Diameter Inches 0.625
Gage 16 16 16
2.75 3.5
All cylinders are of Shelby steel tubing and A is soft-annealed. I n the center of one of the Transite plates, TThich serves as the
bottom of the furnace, is inserted a brass inlet for compressed air. There is another hole for the electric cord and tn-o smaller ones on either side for binding posts. The upper Transite plate has a single hole in the center for an air outlet. At each of the four corners of both Transite plates is a hole to accommodate a steel rod, E, which serves to bind the furnace together and to hold it down to its stand. The stand may be of any design but it should be about 10 inches high, rather heavy, and mounted on a flat Transite board. -4Transite cover, hinged a t the top, and three separate plunger rods, F , topped with brass pistons fitted to the inner walls of tubes A , complete the furnace. These rods are 12 inches long and serve not only to support the glass bomb tubes in the furnace but also to push them out. They may be equipped with wooden handles.
Windings and Connections The three heating units are separately M-ound and should be as identical as possible. For each a strip of asbestos paper 3 inches wide and 11.5 inches long is thoroughly wetted and firmly wapped around the steel tube. Repeated xinding of thin copper wire (later removed) serves to secure the soft, wet asbestos until it can be baked dovin hard by drying in the oven. This asbestos must be thoroughly dry before the electrical resistance is \vound. The heating wire used is No. 37 Nichrome ribbon, which has a resistance of 2 ohms per foot. This ribbon is fastened about 1 inch from the end of the asbestos-covered tube by binding it doxn with heavy copper wire vhich is wrapped over a part of one turn and twisted on the other side. 'The resistance of the coil should finally be 30 ohms, representing a stretched length of about 15 feet. .4 second asbestos wrapper (4.5 inches wide) is now put on, baked, and secured n i t h two or three turns of heavy copper wire. After the completed coils are set into the bottom plate, the Sichrome ends are welded together to form series connections. TABLEI.
DATAON FURNACE
Room temperature 300' C. 300' C. with auxiliary resistance Total Time of Heating Min. 0 12 15 20 25 30 45
Temperature
c.
30 230 250 280 300 320 358
R Ohms 78 89.5
ELECTRIC MICRO-CARIUS FURNACE
1.41 1.23 1.02
107.5
Time of Cooling .Win.
Temperature O
c.
0 10 15
333 100 40
..
... ...
..
..
..
Auxiliary Resistance On 60 70 80 90 100
I .4mpe~es
...
... ... ... ... ... ...
