ANALYTICAL EDITION
SEPTEMBER 15, 1935
333
Correlation of Extrusivities and Other Data
Acknowledgments
Before comparing extrusivities, it was necessary to secure a factor that would place extrusivities determined by the No. 4 and No.5 orifices on a comparable basis. The extrusivity of coal 57 was measured at the temperature of maximum plasticity, 420' C., with both the No. 4 and No. 5 sizes of orifice. From these tests it was found that extrusivities measured by the No. 4 orifice should be reduced by the factor 0.4 to make them comparable to extrusivities measured by the No. 5 orifice. No attempt was made to correct the one value with the No. 3 orifice because of its large diameter and the high pressure that was used with it. In Table V the coals have been arranged in order of decreasing percentage of volatile matter. The volatile matter gives only a rough indication of the degree of extrusivity. Coal 1 with the highest percentage of volatile matter is almost nonfusing and coal 57 develops much less extrusivity than coal 54, although coal 57 has a higher volatile content. There is an approximate correlation between extrusivity and the temperature of initial softening and the temperatures maximum pressure as measured by the gas-flow test; extrusivity decreases as these temperatures rise.
The authors wish to express their appreciation of a fellowship to the junior author granted by the National Fuels Corporation, New York, N. Y. Thanks are due G. A. Berry, vice president, Calco Chemical Company, Bound Brook, N. J., for helpful aid in the design and construction of the extrusivity apparatus.
Literature Cited (1) Ball. A. M.. a n d Curtis. H. A.. IND. ENG.CHEM..22.137 (1930). (2) Bunte, K., a n d Lohr, H.,Gas'u. Wusserfuch,77; 242 (1934). (3) Ibid., 77, 261 (1934). (4) Davidson, W., Fuel, 9, 489 (1930). (5) Foxwell, G.E., Ibid., 3, 122 (1924). (6) Layng, T. E., and Coffman, A. W., IND.ENG. CHEM., 19, 924 (1927). (7) Ibid., 20, 165 (1928). (8) Layng, T. E., and Hathorne, W. S., Ibid., 17, 165 (1925). (9) Lloyd, T. C., Chem. & Met. Eng., 37, 169 (1930). (10) Porter, H.C., Proc. Intern. Conf. Bituminous Coal (1931). (11) Van Brunt, C., J. Am. Chem. SOC.,36, 1448 (1914).
RECEIVED May 31, 1935. The experimental data used in the present paper are taken from a dissertation submitted by J. H. Lum to the Graduate School of Yale University in 1932,in partial fulfillment of the P6.D. requirements.
Plastic Condition at Maximum Pressure
It will be noted in Table V that the temperatures of maximum pressure in the gas-flow test are in most cases less than the temperatures a t which maximum extrusion occurs. This difference is important in view of the fact that the point of maximum pressure has been stated by some investigators to be the:end of plasticity and the beginning of coke formation.
Estimation of Chloramine in Water Supplies
TABLTO V. CORRELATION OF EXTRUSIVITIES AND OTHER DATA Coal No.
1 54 57 55 56 52
--Extrusion Tests--Gas-Flow TestInitial temp. Volatile Initial Maximum for max. Average matter fusion pressure extrusion extrusion % O C . oc. 0. G./min. 39,l 400 415-35 Not su5ciently plaatic 430 1.59 415 36.1 385 0.48 425 420 36.1 395 1.17 415 420 34.8 375 440 0.24 440 22.3 400 500 1.15" 490 17.5 440
a Uncorrected value obtained from the No. 3 orifice and by application of high pressure.
The difficulty of obtaining true coal temperatures in the extrusion test has been pointed out. To eliminate the possibility that the methods of measuring coal temperatures in the gas-flow and extrusion tests were not comparable, the extrusion apparatus was changed to permit carrying out both tests in the same apparatus in a single experiment. A length of brass tubing was wrapped around the outside of the fusion tube, 0 (Figure 9) to serve as a preheating coil for nitrogen. The lower end of the preheating coil was fitted tightly into the orifice below the coal charge and the usual procedure for the gas flow test was then followed. When the gas pressure had reached a maximum value and had begun to fall, the nitrogen tube was pulled away from the orifice, the pistoninserted, and extrusion allowed to take place. By these combined gas-flow and extrusion tests, in which the possibility of error from the method of measuring coal temperature had been eliminated, the following data were secured and clearly show that coals are in a plastic condition at temperatures higher than that of the maximum gas pressure in the gas-flow test: Coal Temperature of maximum gaa pressure, Temperature of start of extrusion, C. Time of extrusion minutes Amount of extrusion, grams Extrusivity, grams per minute
C.
55 415 425 4.5 3.9 0.87
54 427 427 5.0 4.3 0.86
PAUL D. McNAMEE United States Public Health Service, Cincinnati, Ohio
T
HE widespread use of chloramine instead of chlorine for
the disinfection of water supplies renders a distinctive test for chloramine desirable. At present, the chloramine content is measured by the o-tolidine test for residual chlorine. The limitations of this test are well known and interference by nitrite ions is especially notable. AS pointed out by Hulbert (S), nitrite is usually formed in chloramine-treated water. The hydrogen-ion concentration determines the type of chloramine present. According to Chapin (a), a t pH 8.5 or above only monochloramine is formed and below pH 4.4 only nitrogen trichloride is produced. Between pH 4.4 and 8.5, mono- and dichloramine coexist in a ratio fixed by the pH of the solution. When sufficiently acidified, a solution of monochloramine is converted t o nitrogen trichloride according to the equation 3Ji"zCl
+ 2H+ + 2NH4+ + NCli
Marckwald and Wille place in two steps: 2NHzC1 NHzCl
(4) infer that the above reaction takes
+ 4HC1 +2NHaC1 + 2Cla + 2Cla + NCls + 2HC1
(1)
(2)
and that the reaction is catalytically accelerated by liberated acid. In dilute solutions of chloramine, this reaction is very rapid, less than 1 minute being required to convert monochloramine to nitrogen trichloride a t 15' C. As indicated by the above equations, the chloramine content of a solution may be measured by determining the amount of ammonium ion formed on acidification. When the pH of a monochloramine solution is lowered to 4.4 or
INDUSTRIAL AND ENGINEERING CHEMISTRY
3 34
below, two-thirds of the nitrogen present as chloramine is converted to ammonium ion. The chloramine-chlorine content is then obtained by multiplying the observed increase in ammonia-nitrogen by 3/2 X 35.5/14 or 3.8. When 50ml. Nessler tubes are used, the factor becomes 3.8/5 or 0.76, which for convenience may be considered 3/4. (The Nessler tube readings correspond to milligrams of nitrogen per liter when 10-ml. samples are read.)
VOL. 7, NO. 5
proposed method showed 0.22 p. p. m. of chloramine chlorine, while the o-tolidine method gave an apparent chlorine content of 0.45 p. p. m. Solutions containing varying amounts of nitrite but no chloramine all gave negative results with the proposed test, while the readings obtained with the 0-tolidine test varied with the nitrite concentration. With solutions containing both chloramine and free chlorine, the test indicates only the chloramine.
Procedure
Estimation of Free Chlorine
Two 50-ml. Nessler tubes are filled with the solution to be examined. To one tube is added enough sulfuric acid (0.2 ml. of 1 to 10 solution) to lower the pH below 4.4, and the contents are mixed by inverting the tube, which is allowed to stand 1 minute. If the pH of the original solution was below 8.6, a small amount of sodium carbonate (0.1 ml. of 5 per cent solution) is added to the other tube and the contents are mixed. Two milliliters of Nessler reagent (1) are then added to each tube. The tubes are inverted t o insure complete mixing and are compared with the standards after 1 minute. It is essential that the tubes be read not later than 1 minute after addition of Nessler reagent. A set of permanent standards ( 1 ) is prepared to match the colors developed in 1 minute by known amounts of ammonia and 2 ml. of Nessler reagent. Approximately 90 per cent of the full color is developed in 1minute at 20’ C.
When free chlorine is present its amount may be determined by adding enough ammonia to the sample to convert all the chlorine to chloramine and then again determining the chloramine present. The difference in the two determinations is a measure of the original free chlorine. Results obtained on solutions prepared from known amounts of ammonium ion and chlorine are shown in Table TTT
111.
OF FREE CHLORINE TABLE111. PRESENCE
AmmoniaNitrogen Chlorine Added P. p . m.
Effect of Time
Added P . p . m.
Reading of Tubes Acid
Alkaline
Chloramine Chlorine aa Found
P. p .
m.
Theory P. p . m.
The effect of allowing the tubes to stand after the addition of Nessler reagent is shown in Table I. TABLE I. EFFECTOF TIME Time Min.
Reading of Alkaline Tube
Readin of Acicf Tube
Difference in Readings, A
1.6 1.7 1.8 1.8 1.8
1.0 1.0 0.9 0.8 0.4
Chlorine aa Chloramine, 0.76A
P. p . m.
0.5 1.0 3.0 5.0 10.0
0.6 0.7 0.9 1.0 1.4
0.76= 0.76 0.68 0.61 0.30
The o-tolidine test gave a reading of 0.80 p. p. m.
Marckwald and Wille librium, ”$1
(4) assume the existence of an equi-
+ HzO e NHI + HClO
Removal of the ammonia by any reagent would impel the reaction toward the right. Fortunately, this reaction proceeds at a much slower rate than the production of color by Nessler reagent. Since the test depends on the difference in the readings of two tubes, both of which are becoming darker, the error introduced by a delay of one minute is very small. Serious errors are introduced, however, if the tubes are not read for several minutes.
In this ex eriment varying amounts of a stock solution of ammonium cgloride were added to ammonia-free water which contained 1 ml. of 5 per cent sodium carbonate. The chlorine solution was then added and the volume was brought to 1 liter with ammonia-free water. The chlorine content of the stock solution was determined iodometricall . To that preparation w h i d had been found to contain 0.15 p. p. m. of chlorine as chloramine there was added an additional 0.12 p. p. m. of nitrogen as ammonium chloride. The chloramine chlorine content was then found to be 0.45 p. p. m. On subtracting 0.15 from 0.45, the value of 0.30 p. . m. was obtained for free chlorine in the original material. ictually there was added 0.50 p. p. m. of total free chlorine, so that there should have been 0.50-0.13 or 0.37 p. p. m. of free chlorine.
Sensitivity This test for chloramine is not as sensitive as the o-tolidine test for free chlorine. Good results are obtained when the solution contains 0.2 mg. of chloramine chlorine per liter. The presence of relatively large amounts of free ammonia in the sample naturally reduces the precision of the test and for this reason it is of little value when applied to sewage o r sewage-plant effluents.
Comparison with o-Tolidine Test
Summary
With relatively pure solutions of chloramine, the agreement between the proposed procedure and the o-tolidine method is excellent, as is shown in Table 11.
Chloramine may be estimated through a determination of ammonium ion formed therefrom on acidification. The described method is especially useful in presence of nitrite and for differentiation between chloramine and free chlorine.
TABLE11. COMPARISON OF PROCEDURES Teat Employed +Tolidine Proposed
Chlorine &a Chloramine, P. p. m.
Literature Cited
0.32 0.35 0.30 0.27 0.38 0.37 0.30 0.30 0.30 0.38 0.30 0.22 0.38 0.38 0.30 0.30
In this experiment, Cincinnati tap water was used, the nitrite-nitrogen content of which varied between 0.001 and 0.003 p. p. m. With a solution containing 0.2 p. p. m. of chloramine-chlorine and 0.5 p. p. m. of nitrite-nitrogen, the
(1) Am. Public Health Assoc., “Standard Methods of W a t e r Analysis,’’ 7th ed., p. 14 (1933). (2) Chapin, R. M., J. A m . Chem. Soe., 51, 2112 (1929). (3) Hulbert, R.,J. A m . Water Works Assoc., 26, 1638 (1934). (4) Marckwald, W., and Wille, M., Ber., 56B, 1319 (1923). RECEIYZD May 27, 1935.
A & V
