ANALYTICAL EDITION
290
content in the waters of the several stations. The chlorinities of the waters of the Strait of Juan de Fuca are greater than those of Haro Strait, and those of Haro Strait are greater than those of the San Juan Archipelago. The data represent the average of four stations in each body of water. The stations in Haro Strait were taken to the westward of San Juan Island. These stations are characterized by their greater depth and the exceedingly marked turbulence of the waters produced by the strong tidal currents striking the almost perpendicular submarine cliffs off the shore of the island. TABLE 11. IRON CONTENT OF WATERS OF STRAIT OF JUAN DE FUCA, HAROSTRAIT,AND SANJUAN ARCHIPELAGO STRAITOF
JUAN DE FUCA
DEPTH Temp. 1 10 25 50 100 150-200 300
C1
Fe
11.83 16.18 0.037 10.86 16.71 0.050 10.10 17.26 0.050 8.32 18.15 0.050 7.40 18.46 0.088 6.93 18.71 0.280
HAROSTRAIT Temp. C1 Fe
SANJUAN ARCHIPELAQO Temp. C1 Fe
10.68 16.81 0.042 10.35 16.95 0.068 10.32 17.09 0.083 9.66 17.26 0.089 8.92 17.65 0.110 8.53 17.99 0.115 8.35 18.04 0.188
14.58 15.01 0.030 13.05 15.66 0.040 11.87 16.32 0.045 10.45 16.95 0.065 9.65 17.34 0.085 9.10 17.66 0.085
Unpublished data of Lyman D. Phifer, phytoplanktonist for the Oceanographic Laboratories, show that there is a marked abundance of diatoms in the surface water layers of the Strait of Juan de Fuca to depths just below 25 meters. The plankton are distributed throughout the water mass in larger quantities in Haro Strait and the tidal channels of the Archipelago, and exist in still greater abundance in the estuaries of the latter. The data in Table I1 indicate that the iron is actually removed from the water by microscopic plants and that iron may be an essential element for their growth. This is further substantiated by the data in Table I, which show that the iron was completely absorbed by the growth of the diatoms contained in the samples taken in East Sound.
Vol. 4, No. 3
Figure 1 shows the distribution of iron in the waters of the Strait of Juan de Fuca, Haro Strait, and the San Juan Archipelago. The bottom waters of the Strait of Juan de Fuca have a relatively greater iron content than the waters from other depths and areas. The graph illustrates the partial mixing of these waters with those of the surface layers as they reach the deeper and more turbulent condition of Haro Strait. A similar presentation of either temperature or chlorinity data would show the same result.
LITERATURE CITED (1) Braarud and Klem, Skrifter Norske Vklenslcaps-Akad. Oslo. I . Mat.-Naturv. Klasse, 1-88 (1931). (2) Gautier and Clausman, Compt. rend., 158, 1831 (1914). (3) Girard, Chimie & industrie, Special number, 354-585 (February, 1929). (4) Harvey, H. W., J . Marine Biol. Aasoc., 13, 953-69 (1925); 14, 71-88 (1928). (5) Harvey, H. W., “The Biological Chemistry and Physics of Sea Water,” Macmillan, 1928. (8) Leeper, G.W., Analust, 55, 370 (1930). (7) Orton, J. H., Marine BioZ. Assoc. Series, 2, No. 3, 8 (1923). (8) Ossian, H., Pharm. Centr., 13, 205 (1837). (9) Schlesinger and Van Velkenburgh, J. A m . Chem. SOC.,53, 1212-16 (1931). (10) Smith, G. McP., “Quantitative Analysis,” revised ed., p. 133, Macmillan, 1922. (11) Thompson, T. G., J . A m . Chem. Soc., 50, 681 (1928). (12) Thompson and Johnson, Publ. Puget Sound Biol. Sta., 7, 34588 (1930). (13) Thompson, Lang, and Anderson, Zbid., 5, 277-92 (1927). (14) Thompson, McCorkell, and Bonnar, “Contributions to Marine Biology,” p. 82, Stanford University Press, 1930. (15) Thompson and Wright, J . Am. Chenz. Soc., 52, 915 (1930). (16) Thomson, C. W., “Report of the Scientific Results of the Voyage of the H. M. S. ‘Challenger’ 1873-1876,” Physics and Chemistry, Vol. I, Neil1 & Co., Edinburgh, 1884. (17) Vernadsky, W., Rev. gBn. sci.. 35, 7 (1924). (18) Wattenberg, Ber. Zeit. Gesell. Erdkunde, 5-6, 308 (1927). December 11, 1931. RECEIVED
Determination of Alkalinity in Boiler Waters A Comparison of Methods FREDERICK G. STRAUB Chemical Engineering Division, Engineering Experiment Station, University of Illinois, Urbana, Ill.
M
CKINNEY (5) questions the accuracy of the standard methods which have been used in the analysis of boiler waters and suggests a new method of calculating the distribution of the ions which he terms the “equilibrium method.” I n order to compare the results obtained when using the standard methods of analysis and his method, he prepared synthetic solutions and analyzed them using the A. P. H. A. and Winkler methods of analysis. I n Table V, page 196 (6), he gives the results of these data and calculations, results which would indicate, especially from sample 1, that the old standard methods are open to an exceptionally large error. Since the original data are not given, one must assume that 0.02 N acid was used, and 100 cc. of the sample was used for titration. Based on these assumptions, the amount of acid necessary to titrate the synthetic solution, allowing for the slight increase in carbon dioxide above that actually added as sodium carbonate, would be 44.6 cc. for the phenolphthalein end point and 50.7 for the methyl orange end point. However, to obtain the values reported these would have been 94.9 cc. for phenolphthalein and 104.4 for methyl orange end point. Such errors are
certainly not probable in the regular A. P. H. A. titration using synthetic solutions. However, if the results reported had been miscalculated so that they were actually sodium carbonate and sodium hydroxide instead of carbonate and hydroxide as reported, a recalculation would give COa = 60.8 p. pa m. against 69 calculated to be present; and OH = 123 p. p. m. against 131 calculated to be present. This agreement is within reasonable limits. If this were so, the titration figures would be phenolphthalein = 41.6 and methyl orange = 47.0 cc. of acid, which agree fairly we11 with the values calculated for the synthetic solutions. The use of the pH value for calculating hydrate concentration is open to much error, for this value cannot be definitely determined within an error of ~ 0 . 1 ,and often an error of 0.5 is possible. Assume that an accuracy of 0.1 ic possible. Thus, with B solution having a pH of 11.75 as calculated in (e), page 195, the value for 11.75 and activity of 0.87 would be 6.507 millimoles of hydroxide or 260 p. p. m. sodium hydroxide. If the pH determined were 11.85, the result would be 7.127/0.87 = 8.18 millimoles of hydroxide
July 15, 1932
INDUSTRIAL AND ENGINEERING CHEMISTRY
291
TABLEI. COMPOSITION OF SYNTHETIC SOLUTIONS S o h . no.
1
1A
1B
2
2A
NaOH NanCOs NaCl NazSOb POI Si02
2.36 0.84 1.00 2.46
2.36 0.84 1.00 2.46 0.75
2.56 0.93
7.90 1.06 5.00 7.00
7.85 1.08 5.00 7.00 1.00
NaOH NazCOa NaCl NaaBOr POI Si02
94 89 5s 350
94 89 58 350 71
316 113 293 995
314 115 293 995 95
1.00
2.46 0.75 0.50 102 99 58 350 71 30
2B 3 Mzllzmoles p e r lzter 8.75 14.95 1.19 3.02 5.00 5.00 7.00 25.60 1.00 1.95 Parts per million 352 598 121 320 293 293 995 3630 95 117
or 327 p. p. m. sodium hydroxide, an error of 25.8 per cent. An error of the same order of magnitude occurs in the calculation of HCOa- in this pH range. At lower pH values the COacalculation is similarly affected by an error of 0.1 in the pH. This would indicate that the use of this method is certainly not to be recommended until more accurate methods of determining pH values can be placed in the hands of the plant or routine laboratory operators. It has been known for a t least the last 16 years that the alkalinity values obtained by ordinary titration methods do not give all the desirable information in regard to the solution being tested and that the additional information given by the pH value is often desirable. However, for the reasons already given, it has not been considered advisable to rely entirely on the pH value. The two methods of testing solutions give supplementary data, and neither method is absolutely independent of the other. The A. P. H. A. and the Winkler methods of determining alkalinity have been used as standard methods for years. However, if errors as large as those reported by McKinney are probable, the methods are certainly not to be considered as standard. I n order to determine the relative accuracy of the A. P. H. A., the Winkler, and the equilibrium methods, tests have been made on various solutions. These solutions were not limited, as in McKinney's work, to dilute synthetic solutions, but also included boiler waters having concentrations commonly encountered in power plants. METHODSOF ANALYSISTESPED The methods of analysis tested were: (1) the alliaiiiiity (hydrate and carbonate) determination recommended by the American Public Health Association ( 1 ) with corrections applied for phosphate when present; (2) the Winkler method for hydrate and a modification of this method for carbonate (4, 6 , 7 ) ; and (3) the equilibrium method, both short and complete, recently discussed by McKinney and Hecht (3, 5 ) . The determination of phosphate by a direct titration method was also used. SOLUTIONS USEDFOR COMPARATIVE ANALYSIS The solutions used for the comparative analysis consisted of twelve synthetic solutions of known composition similar to boiler concentrates and eleven boiler concentrates obtained from power plants in various parts of the United States and Canada which were representat'ive of the various types of boiler waters encountered in operating plants. The synthetic solutions were made up by using redistilled water with low carbon dioxide content in paraffined bottles, and adding the desired reagents in definite amounts. The total carbonate was determined by evolving the carbon dioxide from a known volume of the solution, absorbing it in ascarite, and weighing. The solutions contained sodium hydroxide, sodium carbonate, sodium chloride, and sodium sulfate. After four solutions of various compositions of these salts were analyzed by the test methods, definite amounts of trisodium phosphate were added, and the solutions analyzed
3A
3B
4
4A
4B
14.95 3.02 5.00 25.60 3.75
16.38 3.18 5.00 25 BO 3.75 3.00
39.40 14.80 15.00 75.30
39.40 14.80 15.00 76.30 3.75
41.34 14.80 15.00 75.30 3.76 3.88
598 320 293 3630 356
655 338 293 3630 356 181
1575 1568 876 10680
1575 1568 876
1654 1568 876 10680 356 233
10680
356
again. Then definite amounts of sodium silicate were added and the solutions analyzed again. Thus results were obtained with solutions free from phosphate and silicate as well as with solutions having these salts present. The composition of the twelve synthetic solutions in millimoles per liter and parts per million is given in Table I.
PROCEDURE IN MAKINGANALYSES The analyses of the synthetic waters were run in duplicate by three different analysts. The solutions were titrated in Erlenmeyer flasks using approximately 0.05 N acid. The A. P. H. A. tests were made by titrating with phenolphthalein indicator to colorless and methyl orange indicator to the first color change. When phosphate was present, 5 cc. excess of acid were added after the methyl orange end point was reached, the solution boiled for 3 minutes, cooled, and titrated with standard sodium hydroxide, until the first appearance of a reddish color similar to the alkaline color of phenolphthalein. A blank run using distilled water and carried through all of the steps of the procedure applied to the regular samples familiarized the operator with the end point and provided the correction allowance for the excess acid added. The difference between the amount of acid used and the blank was taken as a measure of the phosphate. The Winkler test was run by adding 5 cc., and in the more concentrated solutions 10 cc., of a standard solution of sodium hydroxide containing about 10 per cent barium chloride to the sample of boiler water in an Erlenmeyer flask. The flask was then stoppered, let stand a t least 15 minutes, and then titrated with the standard acid solution until colorless with phenolphthalein indicator. The short equilibrium method tests were run using bromocresol green and thymol blue indicators with a Hellige-Klett pH comparator modified according to McKinney and Hecht (3) The pH value was determined by use of the hydrogen electrode. Whenever the pH value was within the range of the colorimetric pH comparator, it was also determined colorimetrically. The solutions were analyzed for sulfate, phosphate, chloride, and silica by standard laboratory methods. These determinations were made by only one operator. The boiler waters were run by only two operators and not in duplicate. The agreement of the results obtained by the two operators was within the experimental error in the majority of the boiler water tested. Consequently duplicate analyses were not run. CALCULATIONS OF RESULTS A. P. H. A. METHOD. The amount of acid used t o reach the phenolphthalein end point is designated as P, and the total required to reach the methyl orange end point as M . N represents normality of the acid, V the volume of solution tested, and PO1 the phosphate content in p. p. m. The calculations involved in the absence of phosphate are as follows :
ANALYTICAL EDITION
292
Na2COs,p. p. m. = NaOH, p. p. m.
=
106 X 1000 X N
V 40 X 1000 X V
NazCOs, p. p. m. =
40 X 1000 X N ( 2 p
V
-
95 X 1000 X N
NazCOa,p. p. m. =
40 X 1000 X N
)
(pw - B )
(3)
(4)
V 106 X 1000 X N
V
(M
pH = log OH p. p. m. 17
- - 95 X
1000 X N
)
(5)
During the preparation of this material, R. W, Fisher, of Baltimore, called the attention of the author to an error in this method which explains why the carbonate determined in this manner tends to be low when phosphate is present. I n the ordinary titration to the P end point, all of the hydroxide, one-half of the carbonate, and one-third of the phosphate are supposed to be titrated. Thus, when the hydroxide determined by the Winkler method is subtracted from this amount, the remainder should be one-half of the carbonate and onethird of the phosphate. If the phosphate is determined, the carbonate can be calculated. However, unless the pH of the solution is above 12, there is less than one-third of the phosphate titrated, since it will not be completely converted to trisodium phosphate below a pH of 12. This means that TABLE11. AVERAQENa2C03 AND NaOH
s 11
NaOH, p. p. m. = OH X 40 17
(7)
~
The sodium carbonate is determined by the equation: COa,p. p. m. = (V2 - VI) 12.32
- 0.813 - 0.626 PO4 (p. p. m.) (8)
NazCOs, p. p. m.
V
WINKLERMETHOD.If the amount of acid necessary t o titrate the solution after adding a definite volume of standard sodium hydroxide solution containing barium chloride is designated as Pw,and B represents the amount of acid needed to neutralize the standard sodium hydroxide added, then NaOH, p. p. m. =
3
when V Z- VI = cc. of 0.02 N acid necessary to titrate 100 cc. of solution from a pH of 8.5 to 5.0.
106 X 1000 X N
(M-P-
KO.
when one-third of the phosphate is subtracted, the carbonate will be low. SIIORTEQUILIBRIUM METHOD.The sodium hydroxide is determined by the equation
- P) N (2p (M
If phosphate is present, the calculations are based on the fact that when a solution containing hydrates, carbonates, and phosphates of sodium is titrated with acid to the P and Mend points, the amount of acid required between the P and M end points is equal to one-half the carbonate and one-third the phosphate (6). The calculations for hydrate and carbonate in the presence of phosphate are as follows: NaOH, p. p. m. =
voi. 4,
BY
=
COS X 106 60
(9)
The complete equilibrium method calculationfi are described in detail by McKinney (6). The sodium hydroxide from the pH value is calculated from the same formula as the one used in the short method, Equations 6 and 7, except that allowance is made for the fact that the activity is not equal to 1. To determine the activity, a knowledge of the composition of the solution is essential. I n these tests this calculation is made only on the synthetic solutions, since there are not sufficient data available to calculate the activity in the boiler waters. DETERMINATION OB PHOSPHATE BY DIRECTTITRATION. The amount of alkali necessary to back titrate the A. P. H. A. test sample which has had 5 cc. excess of acid added after the M end is reached, is designated by A . B equals the amount of acid used to back titrate the blank, and Nc equals the normality of caustic solution used. PO,, p. p. m.
=
95 X 1000 X Nc (A V
- B)
RESULTSOF ANALYSES The average results of the analyses on the synthetic solutions and the boiler waters are given in Table 11. Table I11 shows the per cent error in the sodium carbonate and sodium hydrate contents for all the solutions tested. The per cent error in the sodium carbonate content of the synthetic solutions illustrates that the A. P. H. A. and the short equilibrium method both show good agreement with the actual content. I n order to check this further, the average (Vz - VI)and (M - P ) readings were compared. This is done
DIFFERENT METHODSIN SYNTHETIC SOLUTIONS r n BOILER ~ WATERS (Parts Der million)
July 15, 1932
INDUSTRIAL AND ENGINEERING CHEMISTRY
in Table IV. The difference between (Va - VI) and ( M - P) is calculated in per cent of (V Z- VI). The maximum per cent error of any one determination from the average for ( V , - VI) and ( M - P ) is also shown. These results show very good agreements, and indicate that for the waters analyzed the equilibrium and A. P. H. A. methods are equally satisfactory. In the synthetic solutions the (V Z- VI) average maximum error was 1.9 per cent, whereas that of the ( M - P ) reading was 0.6 per cent. For the boiler waters the errors were 4.4 and 3.6, respectively, thus showing that the A. P. H. A. determination with the use of much less expensive equipment gave results as close as the method involving the use of the color comparator.
293
The results tabulated in Table I V show that the ( V z- VI) and ( M P ) readings are almost identical for the synthetic solutions and show good agreement in the boiler waters. The maximum difference between these two equations should come in low concentration. Thus, if the figures obtained in water 112, (VZ- VI) = 083 and ( M - P ) = 0.80, were substituted in their respective formula with POc = 0, the results are as follows: COS by A. P. H. A. = 22.4 p. p. m. COa by equilibrium = 23.0 p. p. m.
-
which agrees within the experimental error. If phosphate is present as in water lA, then: COSby A. P. H. A. = 48.4 p. p. m. TABLE111. ERRORIN NazCOa AND NaOH CONTENT FOR COa by equilibrium = 51.6 p. p. m. SOLUTIONS TESTED which agrees within the experimental error. The calculation ERROR IN NanCOa CONTENT ERROR I N NaOH CONTBNT of the carbonate by the short equilibrium method applies Short ShoSt equiequicorrections to the older method which are less than the WA’rmR A. P.H.A. Winkler librium A. P. H.A. Winkler librium experimental error. Consequently, the results agree very % % % % % % 1 - 5.5 - 2.5 -5.5 3.2 2.1 -36.0 6.3 closely with those obtained by the older method. lA - 3.4 -53.0 2.2 17.0 2.1 1B -13.0 38.0 The carbonate as determined by the combination of the 3.0 13.0 11.0 3.0 2 10.0 2.7 2.7 1.9 -2.0 -28.4 Winkler method with the P determination of the A. P. H. A. 2A 6.2 -39.0 4.3 -2.9 2.2 -10.1 - 4.9 2B 4.1 6.6 -1.1 0.0 +29.0 method, gave good results in the absence of phosphate and 3 1.0 8.6 3.0 -0.6 -29.0 -2.3 silicates. The presence of phosphate tended to decrease the 8.7 3A 1.0 0.3 -0.3 3.5 1.6 3B -- 2.9 13.0 2.9 +0.3 -21.0 -1.1 amount found, whereas the addition of silicate increased the - 0.1 1.7 0.1 4 -28.0 1.9 1.2 1.6 5.3 4A 2.2 3.0 0.4 1.6 carbonate determined. 4B - 4.0 +13.0 1.5 -3.6 1.9 3.3 The reported carbonate in the boiler waters was very interesting. I n samples 108, 109, 110, and 111, the results TABLE IV. COMPARISON OF ACCURACY OF DETERMININO (Vt - VI) AND (M - P ) VALUESIN ALL WATERS are fairly close to the actual carbonate present. Any one of the methods appears to give accurate results. These boiler (Vz-Vd ( M - P ) MAX. MAX. waters contain appreciable amounts of alkalinity, low organic ERROR ERROR tv2-vl) (M-P) (V*-Vd-(M-P) FROM FROM matter, and no phosphate. They are typical of the boiler WATER Av. Av. (Va-71) Av. Av. waters found in lower pressure industrial plants. The results % % % 1 1.67 1.70 on all the other boiler waters showed that none of these -1.8 4,s 4.8 1A 3.35 3.31 1.2 4.8 0.6 methods gives concordant carbonate results in low concentra1B 3.42 3.27 +4.3 3.8 10.0 2.52 2 2.35 -7.0 15.0 7.0 tions. 4.52 2A 4.37 -3.2 4.1 1.7 ZB 4.63 4.65 The sodium hydroxide results obtained on the synthetic -0.4 2.6 0.0 3.27 3 3.28 $3.0 3.6 1.8 waters by the A. P. H. A. method were very accurate. The 7.20 7.20 0.0 3A 7.5 2.2 3B 7.25 7.24 0.1 0.8 0.1 Winkler method also gave very good results. The short 4 7.77 7.83 0.8 0.6 0.2 4A 9.81 9.77 equilibrium method gave very erroneous results. I n the -0.4 2.3 0.1 9.57 4B 9.71 -0.2 1.9 0.6 absence of phosphate, the results were low. With phosphate Av. -0.6 4.3 2.5 present, the results tended to be higher. One would not 101 1.59 1.64 - 3.1 3.8 2.4 expect the hydrate to be correct, since it is assumed that the 102 0.70 1.19 -70.0 0.0 0.6 103 0.67 0.57 +15.0 3.0 0.7 activity is equal to 1, and in most of the waters tested it is less 104 3.23 3.43 - 6.1 1.2 0.0 105 1.26 1.63 than 0.85. This would tend to give low results. At the same -23.0 3.2 1.2 107 2.52 2.72 - 8.0 7.0 4.5 time a large error is introduced with only a small variation in 108 2.90 2.55 1.4 7.0 7.6 109 14.15 13.85 2.1 1.8 1.1 pH determination. Thus, an error of 0.1 in pH means an 110 3.65 3.55 2.7 1.3 0.6 111 2.94 2.71 7.9 error of 25 per cent. I n the boiler waters 108, 109, 110, and 10.6 4.1 112 0.83 0.80 3.8 3.8 0.0 111, the Winkler and the A. P. H. A. methods give good results Av. - 7.0 3.9 2.3 for the hydrate. These are the clean waters which gave good In order to understand why there should be such close carbonate results. The short equilibrium method gives low reagreement of these two methods, it is only necessary to com- sults on the boiler waters 109,110,111, and 112. It is almost pare the formulas for calculating the results. The A. P. H. A. impossible to calculate the activity coefficients for these solumethod, when corrected for phosphate, gives the following tions with any degree of accuracy, and consequently this cor* rection cannot be applied. I n general there is nothing in these equation : results to show that the determination of pH values gives any106 X 1000 X N thing more than an approximation of the hydrate content unless NsCOs, p. p. m. = V corrected for activity, and then in the presence of phosphate or silicate the values would be too high. (M-P(3) 95 X 1000 X N AS some of the waters tested contained phosphate, the amount present was determined both by the standard laboraIf N = 0.02 and V = 100, then: tory procedure and by the back-titration method. It wm Na&Os, p. p. m. = 21.2-(M - P) 0.111 PO,, p. p. m. found that in the synthetic solutions the back-titration method or Goa, p. p. m. = 12.0 ( M - P ) - 0.63 Pod, p. p. m. (11) gave verygood agreement with the standard procedure, whereas Equation 8 for the carbonate by the short equilibrium in the boiler waters the agreement was poor in most cases. It seems as though the presence of organic matter in the boiler method is as follows: waters influences the results obtainable by back titration and COS,p. p. m. = 12.32 (VS VI) 0.813 - 0.626 PO4,p. p. m. introduces errors which cannot be compensated for in the calculation of the results. (8)
)
-
-
-
ANALYTICAL EDITION
294
CONCLUSIOWS The conclusions to be reached from digesting the results of these analyses are: 1. The A. P. H. A. and Winkler methods give reliable hydrate content in the absence of high silica and organic matter. I n the presence of organic matter the Winkler method appears to be the most reliable. 2, The determination of hydrate from the pH value gives erroneous results. 3. The carbonate determined by the A. p. H. A. method is accurate in the absence of organic matter. However, in boiler waters having the sodium carbonate below 50 p. p. m. this method is not reliable. 4. The determination Of carbonate using the short equilibrium method gave results which averaged about the same as those obtained by the A. P. H. A. method. 5. The carbonate determined by the carbon dioxide evolution method gave the most reliable results for carbonate.
Vol. 4, No. 3
LITERATURE CITED (1) American Public Health Association, “Standard Methods of Analyses,” New York, 1925. (2) Britton, H. T., “Hydrogen Ions,” pp. 142-7, Van Nostrand, 1929. (3) Hecht, M. H., and McKinney, D. S., Power Plant Eng., 35, 602-4, 649-52 (1931). ( 4 ) Johnston, J., J. Am. Chem. Soc., 38,939 (1916). (5) McKinney, D. s., h D . E X G . CHEM.,Anal. Ed., 3, 192-7 (1931). (6) Parr, S. W., and Straub, F. G., Eng. Expt. Sta. of Univ. of Ill., Bull. 216, 7 (1930). (7) Treadwell and Hall, “Analytical Chemistry,” Vol. 11, p. 592, Wiley, 1915. (8) Treadwell and Hall, Ibid., Vol. 11, p. 587. RBCEIVED September 10, 1931. Presented before the Division of Water, Sewage, and Sanitation Chemistry at the 82nd Meeting of the American Chemical Society, Buffalo, N. Y., August 31 t o September 4, 1931. Part of the research being oonduoted in cooperation with the Utilities Research Commission, Inc., of Chicago, 111. Published by permission of Director Engineering Experiment Station, University of Illinois.
An Inexpensive Low-Temperature Thermostat FRANK 0. LUNDSTROM AND COLINW. WHITTAKER Fertilizer and Fixed Nitrogen Investigations, Bureau of Chemistry and Soils, Washington, D.
T
HE low-temperature thermostat described in this paper, although inexpensive to construct and to operate, has been found to be accurate and reliable. Liquid ammonia is used as the cooling agent for temperatures between 7 ” and -25” C. This substance is cheap, readily available, and because of its exceptionally large heat of vaporization per unit weight, cools economically. Ice is used to cool the bath for temperatures between 7 ” and room temperature. The method of applying the cooling agent differs from the usual practice in that the heat is conducted away from the bath to the cooling agent by means of a &Der rod soldered through the wall of the bath, which is constructed of copper. The cooling of the bath liquid is thus accomplished by transfer of heat to the container wall, rendering the use of a cooling coil or other device in the bath itself unnecessary. DESCRIPTION OF APPARATUS The bath and its associated apparatus are illustrated diagrammatically in Figure 1. The bath itself consists of a copper tank, a, made by soldering one end of a section of copper tubing 7.5 inches (19.05 em.) long and 3.5 inches (8.89 cm.) inside diameter into a groove turned in a copper disk 4.5 inches (11.43 em.) in diameter. The walls and bottom of the bath are 0.125 inch (0.32 cm.) thick. A 1-inch (2.54-em.) hole is drilled in the wall of t h e b a t h 2.5 i n c h e s (6.35 c m . ) f r o m t h e t o p , a n d t h r o u g h this hole is soldered a 1-inch (2.54-em.) copper rod, b, so that it extends 0.5 inch (1.27 cm.) into the bath. The rod is bent
C.
downward 2.5 inches (6.35cm.) from the wall of the bath, passes through a cork, c, and extends down 8 inches (20.32 cm.) below the bend. The bath and that portion of the rod between i t and the cork are carefully lagged with 1.5 inches (3.81 cm.) of hair felt (not shown). The lagging is somewhat thinner between the rod and the bath to allow clearance for the vacuum bottle. Kerosene is used as the bath liquid. The bath is cooled continuously by inserting the copper rod into a 500-cc. silvered vacuum bottle, d, containing liquid ammonia, or into a beaker of ice and water. The cork, c, fits loosely into the neck of the bottle. Heat is sumlied intermittently by one or t; 21candle power automobile headlight bulbs, f and y, as conditions may require. The switches, o and o‘, are arranged to permit the use of one or both bulbs. The b u l b s , I I which are lighted by a standard 6-volt storage battery, are mounted with special clamps of brass strap, g and g’, which pass around the base of the bulb and are soldered to the 0.125-inch (0.32-cm.) copper rod, h, which passes through the cork, i, and forms one side of the lamp circuit. Copper wires, j and j ’ , are soldered to the other contact of the bulbs and pass through the cork to the insulating bracket, k . The lamp circuit is controlled by the 250-ohm relay, I, the primary circuit of which is operated by a conventional gas type thermoregulator which consists of a gas-filled 20-cc. bulb, m, connected by a small-bore capillary to a closed-end manometer of s l i g h t l y m o r e than barometric height, which was carefully boiled out after being filled with
