1796
ANALYTICAL CHEMISTRY
pooled estimate of the standard devintion, charide was calculated as follows:
,;
for each monosac-
where n is the number of determinations comprising a run, the variance of a run, and k is the number of run8 pooled.
92
is
ACKNOW LEDGXIENT
The authors are indebted to L. C. NassopustandF. W. Faustfor the preparation of drawings and photographs, and to S. W. Schubert for the synthesis of antlirone. This work was eupported by a grant-in-aid from Lakeside Laboratories, Inc., Milwaukee. Ris. LITERATURE CITED
(1) Black, H. C., Jr., ANIL. C H E V 23, , 1792 (1951). (2) Dixon, W. J., and Massey, F. J., Jr., "Introduction to Statistical
Analysis," McGraw-Hill, Xex York, 1951. (3) Gilman, H., and Blatt, 9.H.. "Organic Syntheses," vol. 1 (Coil.), Wiley, New York, 1941.
Hoel, P. G., "Introduction to Mathematical Statistics." Wiley, Sew York, 1947. Johanson, R., AVuTature,172, 966 (19533. Koehler, L. H., ANAL.CHEX.,24, 1576 (1952). McCready, R. hl., Guggolz, Jack, Silviera. Vernon, arid Owens. H. S.,Ibid., 22, 1156 (1950). Morris, D. L., Science, 107, 254 (1948). Morse, E. E., ANAL.CHEM.,19, 1012 (1947). Schonberg, A., and Mustafa, J . Chem. Soc., 1945, 657-60. Schonberg, A., Mustafa, A , , and Zayed. S., Science. 119, 193 (1954). Scott, T. A , . Jr., and Melvin. E. H.. ANAL.CHE!,,.25, 1856 (1953). Seifter, S., Seymour, Dayton, Xovic, B.. and Muntwyler. Edward, Arch. Biochem., 25, 191 (1950). Shetlar, 31.R., ANAL.CHEY.,24, 1844 (1952). Snedecor, G. W., "Statistical Methods." Iowa State College Press, Ames, Iowa, 1946. Trevelyan, W. E . , and Harrison, J . S..Biochem. J . (Lortdori). 5 0 , 298 (1952). Viles, F. J., Jr., and Silverman, L., ANAL.CHECLC., 21, 950 (1949). Youden, W. J., "Statistical XIethods for C'hetnists," Wiley. Sew York, 1951. PreRECEIVED for review Sovember 29, 1R54. .iccepted August 8, 193:. sented in part before the Division of .inslytical Chemistry. 16th XIidwest Regional Meeting of ACS, Omaha, S e b . , Soreniber. 19.54.
Rapid Determination of Carbon Dioxide in Silicate Rocks LEONARD SHAPIRO and W. W. BRANNOCK
U. S.
Geological Survey, Agricultural Research Center, Boltsville,
In the development of rapid methods for silicate rock analysis, a simpler and faster means w-as needed for the determination of carbon dioxide than the conventional "train" procedures. With the method presented here, which involves measurement of the volume of carhon dioxide evolved, the time required for a determination is about 5 minutes per sample. I t provides a saving of 30 to 40 minutes for each determination without significant loss of accuracy.
C
ARBON dioxide in silicate rocks is usually determined by absorbing and weighing the carbon dioxide evolved when the sample is decomposed by acid ( 2 ) . Methods of this type usually require about 45 minutes for a single determination. In the scheme for rapid analysis of silicate rocks developed by Shapiro and Brannock ( 4 ) an ignition loss determination is used in lieu of water and carbon dioxide determinations. I n many inst,ances rock analyses are more useful if values are given for water and carbon dioxide. -4rapid met,hod for the determination of water has been developed (S), and this paper describes a procedure for the determination of carbon dioxide that requires about 9 minutes per determination. The procedure presented is similar to thatdescribed by Fahey (I), in which t,he volume of gas evolved by acid attack on the sample is measured. The ivell-knoTvn qualit,ative test for carbonate, in which the formation of hubbles is observed when hydrochloric acid is added to a test tube containing the ground sample and hot water, has been made quantitative by the use of a tube with a side arm for catching and measuring the gas evolved. APPARATUS
The special tube designed for the determination of as much as 2% carbon dioxide, the range common in silicate rocks, is shown in Figure 1. It consists of a borosilicate glass test tube, 18 by 150 mm., to which is attached a side arm of borosilicate glass, 200 mm. in length and 10 mm. in outside diameter, with a closed end. An electric heater of the Gilmer type with a means of regulating the power input is used to heat t'he sample and liquid in the lower portion of the carbon dioside tube. The heater should be fitted
Md.
n-ith n cover of asbestos board, about 0.29 inch in thickness, with a hole about 20 mm. in diameter in its cent.er
+
REAGENTS
Hydrochloric acid, 1 1. Alercuric chloride, 3%. Motor oil, S.A.E. No. 10. Addition of a s n d l amount of antifoaming agent is desirable although not essential CALIBRATION OF CARBON DIOXIDE T U B E
1. Weigh 1.03 grams of National Bureau of Standards standard sample Y o . 79 and transfer, by means of 3 dry funnel, to the bottom of the carbon dioxide tube. 2. Add 2 ml. of the mercuric chloride solution and tap the tube to free entrapped air bubbles. 3. Add oil t o the oil-level mark. 4. Tilt the tube so that the oil completely displaces the air from the side arm. Then return the tube to a position such that the main part of the tube is vertical. 1 hydrochloric acid, and tilt the tube so 5. Add 2 ml. of 1 that the side arm is vertical to allow any carbon dioside produced to ent'er the side arm. 6. hfount the carbon dioxide tube in a clamp attached t o a support so that the side arm is vertical, and insert the lower part of the tube through the hole in the cover of the heater Lvith the interface of the aqueous and oil phases just a t the level of the cover. (The heater should be preheated so t h a t the temperature around the lower part of the tube can be maintained a t about 189: C.) Allow the aqueous phase to boil for 2.5 minutes. i. Remove the tube from the heater and allow tap water to flow down the outside of the side arm for 15 seconds. (Tap ivater temperature should be between 19' and 25' C.) 8. Remove from the stream of tap water, hold the tube with the side arm upright, and mark the posit,ion of the meniscus on the side arm. This is the 1 % mark. 9. Repeat steps 1 through 8 using 0, 0.206, 0.412, 1.54, and 2.06 grams of the standard sample to obtain calibration marks equivalent to 0, 0.2, 0.4, 1.5, 2.0% carhon dioxide, respectively. 10. The tube can now be marked off by interpolation to give marks for each 0.1% carbon dioxide.
+
PROCEDURE
Transfer 1.000 gram of sample powder t.0 the bottom of the carbon dioxide tube by means of a dry funnel. Proceed as described in steps 2 to i of "Calibration of Carbon Dioxide Tube."
1797
V O L U M E 27, N O . 11, N O V E M B E R 1 9 5 5 Jirmove from thc stream of t a p water and estimate the per cent .irbnn d i o ~ l from e the scale on the side arm. EXPERIM EIVTA L
.4 number uf experiment,s \\.ere made to determine the effects of several pert,inent variables on the evolution and measurement of carbon dioxide from samples of silicate rocks: Three different eupernat#antliquids were tested, three tubes with different sidearm lengths were tried, the time required for sample decomposition was studied, and the feasibility of using mercuric chloride t.o inhibit the format,ion of hJ-drogen, which might result from the reaction between hydrochloric acid and “tramp iron,” was determined.
The results for carbon dioxide in samples contaminated in this wal- are about 0.1 t o 0.2% high if nothing is done to prevent the evolution of hydrogen resulting from the reaction of the metallic iron with the hydrochloric acid added to decompose the carbonates. This difficulty can be overcome by the addition of mercuric chloride solution, which converts the metallic iron to ferrous iron without formation of hydrogen. Table I1 gives a comparison of results obtained for gr:tnite sample when mercuric chloride is added and when it is omitted for the determination of carbon dioxide in portions of sample powder with a normal amount of iron contaminant, with portions of sample from which iron had heen removed by a magnet, and with portions of sample to which an a.bnormally large amount of metallic iron had been added. The data show that metallic iron can cause errors in results for carbon dioxide by volunietric met’hods unless precautions are taken to prevent the formation of gaseous hydrogen and that the difficulty can be overcome very simply by use of mercuric chloride.
Table I.
Effect of Length of Side Arm on Length of Gas Column Length of Gas Column, M m .
Length of Side .4rm, 111ii. 100 200 400
49
30 38 5 29
38 29
Table 11. Effect of 3Iercuric Chloride on Evolution of Gas from Granite Sample Containing Metallic Iron
Figure 1.
Carbon dioxide tube
Tests of Three Supernatant Liquids. Distilled water, 20% iodiuni chloride solution, and motor oil were compared as supernat,ant liquids. Distilled water and sodium chloride solution were usable but, were inferior to oil, especially a t low levels (below 0.5%), because of t.he greater solubility of carbon dioxide in wat.er and sodium chloride solutions. It was also found that wit,h oil it was easier t o control the boiling of the solution in the lower part of the tube. Selection of Suitable Side-Arm Length. Three carlmn dioside tubes were tried. One had the dimensions shown in Figure 1. another was t>hesame except that the side-arm length was 100 nim. The thiid had a side-arm length of 400 mni. Two runs were ma,de with each tube using a sample of rock pon.der containing about. 0 . 5 % carbon dioxide. The results are shoun in Ta.ble I. These results indicat,e that the longer the oil path through a.hich the gas bubbles must travel, the less gas recovered. This may he explained as the soluhility effect of the carbon dioxide in t,he oil. It is evident that the longer the side arm used, the less precisely t,he readings could be made, and that the shorter the Fide arm, t.he less the range covered for a given sanq~lesize. Taking these facts into consideration, in addition to the fact that. t,he t.ube wit,h t.he long side arm was difficult to manipulate, the 200 mm. side-arm length was chosen as the best compromise. Time Required for Decomposition of Finely Ground Samples. Four portions of a sample containing about 1% carllon dioxide were carried trhrougiithe procedure using hoiling p e r i o h of 1, 2, 3, and 5 minutefi. The lengths of the gas columns obtained were 91. 103, 102, and 102 mm.,respertively. Use of Mercuric Chloride to Eliminate Interference of Tramp Iron. Rock smiples which are prepared for anal! with steel grinding apparat,us usually contain a +mall amount of metallic iron int,roduced as a contaminant ti>- the grinding nppara t LIS.
Apparent C o r , %” 11-1th HgCIr Wlthout H g C ! 0.06 0.20 0 09 0.09 0.09 0.39
Treatment of Samplr Powder None Iron removed by magnet 8-mg. iron filings added
’ Csing a conventional train procedure, f i r e analyses averaged 0.07% CO,. Table 111. Carbon Dioxide Determinations by Conventional Train Method and by Rapid Method
cor, % Conventional method 0 19 0 67 0 27 0 05 0 32 0 00 0 76 1 7 1 9 0 06
Rapid riiethod 0 22 0 68 0 28 0 05 0 32 0 06
n
7.5
1 6 1 9 0 06
Difference +0.03 +0.01 +0.01 0.00 0.00 +0.06 0.00 -0.10 0 00 0 00
The experiments indicate t.liat the optimum procedure n.ould be one in which oil is used as the supernatant liquid, the boiling time is a t least 2 minutes, the lengt,h of the side ann o n t,he carbon dioxide tube is about 200 mm.,and mercuric chloride is used to eliminate the interference of metallic iron. RESULTS
I n Table I11 results obtained by this rapid method for a series of samples containing from 0 to 2y0 carbon dioxide are compared with results obtained by conventional train procedures. The results are in good agreement. L I T E H T U R E CITED
(1) Fahey, J. J., U. 9. Geol. Survey, Bull. 950, 139 (1946). (2) Hillebrand, W. F., and Luridell, G. E. F., “Applied Inorganic Analysis,” p. 623, Wiley, S e w Tork, 1929. (3) Shapiro, L., and Brannock. W.IT.,.%SAL. CHEM.,27, 560 (1955). S. Geol. Survey, Circ. 165 (4) Shapiro, L., and Rrannock, W.IT..I-.
(1952). RECEIVEDf o r review May 16, 1953. Accepted July 22, 1955. authorized by Dirertor. U. R . Geological S u r w - .
Publication
