I N D U S T R I A L A N D ENGINEERING CHEMISTRY
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fore upon weak gels rather than upon the hard, firm gels having a gelatin content of 6.67 per cent, that a comparison should be based. The Bloom gelometer uses a circular area 0.5 inch (12.7mm.) in diameter as the surface on which pressure is applied by means of shot during the test. About the lower limit that can be satisfactorily attained with this area is a gel strength corresponding to 15 grams. The strength of gels that are barely able to set and to retain their shape is not possible of measurement with the present instrument. I n order to approach more nearly the desired range, it is desirable to enlarge the circular area on which the weight is applied to a t least double the present diameter, making the test area four times as large as that now in use in the Bloom gelometer. It appears essential to determine the constants K and N for each gelatin sample by gel-strength determinations at two different gelatin concentrations at 0.7" C., at a p H value approximating 6.0, with the usual 0.5-inch (12.7-mm.) area of depression or the one suggested of four times this area. Having determined these constants, the concentration required to give the desired gel strength may be calculated from the equation S = KCN. T a b l e XV-Bloom
S t r e n g t h Values Corresponding to Test-Tube Test GELATINCONCN. CALCD.BLOOM REQUIRED TO STRENGTH CORREFORM GELAT SPONDING TO TEST0.7' C. TUBETEST
K
N
Per cenl
Grams
5 I1
14.96 11.48 6.34
1.6107 1.6319 1.7978
0.55 0.66 0.80
7.37 5.90 4.20
' 19 13 20
16.98 9.65 6.34
1:6266 1.7735 1.7978
0.47 0.63 0.75
4.82 4.46 3.73 Mean 5 . 0 8
SAMPLE
Calfskin
a
Porkskin
'
Table I11 records the gelatin concentration required to form a solid gel in a test tube at 0.7" C. in 24 hours and Table VI1 the constants for six commercial gelatins. As these concentrations gave gels of supposedly about equal strength in the test-tube test to permit inversion of the tube, it seemed desirable to calculate the value of the gel strength corresponding to the test-tube test. An agreement between these values for different gelatin samples would afford a check on the constants determined. These values (Table XV) agree fairly well with each other and with the mean, and
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show that the gel strength represented by the test-tube test corresponds to about 5 grams. Furthermore, this calculation can be made with reasonable assurance into a range which at present cannot be reached experimentally. It would seem that in any case, no matter how large the test area used, eventually resort will need to be made to the gel constants, as the ice-cream manufacturer is interested in the concentration required of a given gelatin for his product, and not in the value of the gel strength it may have a t some empirically chosen concentration. Whether it will prore advisable for the manufacturer t o supply these constants to the consumer and permit him to make his own computations to ascertain the gelatin concentration desired, or whether the required gelatin concentration itself would be a more acceptable figure to the consumer, the writers make no effort to decide. Acknowledgment
The writers wish to acknowledge their indebtedness to the Milligan and Higgins Gelatine Company of New York City for placing at their disposal a Bloom gelometer, and to numerous gelatin manufacturers throughout the country who have furnished the gelatin samples used in these studies. Bibliography I-Smith, J . I n d . Eng. Chem., 12, 878 (1920). 2-Richardson, Chem. Met. Eng., 28,551 (1923). 3-Sheppard, Sweet, and Benedict, J . A m . Chem. Soc., 44, 1857 (1922). 4--Kraemer, Colloid Symposium Monograph, Vol. IV, p. 102 (1926). 5-Levene and Pfaltz, J. Bioi. Chem., 63, 661; 68, 277 (1925). J. Gen. Physicl., 8, IS3 (1925). &Smith, J. A m . Chem. Soc., 41, 135 (1919). 7-Official Standard Methods for Determination of Jelly Strength and Viscosity of Edible Gelatin Manufacturers Society of America (14.57 Broadway, New York, N . Y.). 8-Oakes and Davis, J . I n d . Eng. Chem., 14, 706 (1922). 9-Sheppard and Sweet, J. A m . Chem. Soc., 48, 539 (1921). 10-Levine and Carpenter, J . Bact., 8, 297 (1923). 11-Shaw, Abstracts Bact., 8, 2 (1924). Ia-Bogue, "Chemistry and Technology of Gelatin and Glue," p. COB. McGraw-Hill Book Co., 1922. 13--Hatschek, Kolloid-Z., 7, 301 (1910); 8, 34 (1911); Trans. FuadUy Soc., 9, 80 (1913). 14-Bogue, J . A m . Chcm. Soc., 43, 1764 (1921). 15-Davis and Oakes, Ibid., 44, 464 (1922). 16-S. Arrhenius, 2.physik. Chem., 1, 285 (1887). 17-Bogue, Chcm. Met. Eng., 23, 105 (1920). 18-Frey and Gigon, Biochem. 2..22, 309 (1939). 19--Dahlberg, Carpenter, and Hening, Ind. Eng. Chcm., in press.
Estimation of Stable and Unstable Organic Matter in Sewage-Polluted Liquids' W. E. Abbott LABORATORY OF CHIEFSANITATION CEEMIST,S H A X G H A MUNICIPAL I COUNCIL, CHINA
I
N A recent communication2 the dissolved-oxygen absorption of samples of sewage free from suspended matter up to the point a t which nitrification started wm compared with the oxygen absorbed in Adeney's acid dichromate test3 as modified in this laboratory. The object then was to confirm the completeness of the absorption with pure substances recorded in the new test, assuming that 20 to 30 per cent of the organic matter was converted to "humus." Other classes of liquid have since been thus investi8 f
Received Octoher 25, 1927. Abbott, I n d . Eng. Chem., 19, 919 (1927). Sci. Proc. Roy. Dublin Soc., 18 (N. S.), 199 (1926)
gated with a view to determining the approximate percentage of the carbonaceous matter which undergoes change during the first-stage absorption of polluted liquids by taking the acid dichromate absorption as an a p p r o h a t e measure of the total organic matter. Method of Expressing Dissolved Oxygen Absorbed during Carbonaceous Oxidation
The oxygen absorbed during the first-stage or carbonaceous fermentation of a polluted liquid is not identical with that absorbed up to the point at which nitrification starts, since for several days the oxidation of the last portions of the
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
April, 1928
fermentable carbonaceous matter proceeds simultaneously with the production of nitrite. However, the purely carbonaceous absorption can be represented by the equation4 logLa/L = Kt where La = oxygen absorbed during first stage L = oxygen requirement of sample at time t K = a constant for each sample
In all cases to determine the appropriate equation for the first-stage absorption, several probable values of La were selected tentatively and the resulting log L a / L figures were plotted against the time. That value of La was taken as corrert which gave points lying upon or most symmetrically about a straight line, and was usually about 10 per cent higher than the absorption recorded up to the point a t which the second stage commenced as shown by the production of nitrite. Since La functions as part of a definite equation, it would appear more satisfactory as an expression of the first-stage absorption than the oxygen absorbed up to the production of nitrite. Indeed, excellent reasons could be advanced for adopting La as the most satisfactory single index of strength, since the power of the readily fermentable carbonaceous matter to absorb dissolved oxygen is the most important characteristic of a polluted liquid. Experimental
Part of each sample was incubated a t 21” C., suitably diluted with pure water if necessary, and the dissolvedoxygen absorption determined daily. The appropriate equation was determined therefrom as described above. The diluting mater was also incubated for about 6 days and corrections for this absorption were made in calculating La. Table I gives the experimental data on which the value of La was worked out for two such samples. Unfortunately, in the case of the activated-sludge effluents there is difficulty in representing the first stage by such an equation, owing to the comparatively slight amount of the absorption and its short duration; and therefore the approximate value of La, as determined by inspection of the absorption-time curve and knowledge of the point a t which nitrification starts, wm taken for subsequent calculations. Table I-Dissolved-Oxygen INCUBATION Days
ACTUAL
Absorption D a t a CALCD. FROM 37 log = 0.107 1
L
P. p . m.
RIVER WATER INCUBATED ALONE AT 21‘
2 3 4 5 7
1.41 1.98 2.31 2.58 3.04 3.61° 4.334
C.
1.45 1.93 2.32 2.62 3.04 3.30 3.39
9 10 Lc is therefore 3.7. The dichromate absorption in this case is 8.1. CENTRIFUGED RAW SEWAGE DILUTED WITH 19 PARTS OF WATER 6.5 log 7 = 0.126 f 1.71 1.64 2.87 2.83 3.78 3.82 4.44 4.46 5.33 5.36 5.65 6.03b 6-day absorption of diluting water 0.06. L a is therefore (6.5 0.06) X 20,or 129. The dichromate absorption in this case is 122. Nitrification started between 7 and 9 days. b Nitrification started between 6 and 7 days. L
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represent all of the total carbonaceous oxidizability, it is apparent that La must be a still smaller proportion of the total carbonaceous oxidizability than the figures shown in Table 11. These figures, however, show that in the case of sewages free from suspended matter the first-stage oxidation does represent the oxidation of most of the soluble carbonaceous matter. For crude sewages the proportion is somewhat smaller, as might be expected in view of the nature of the suspended matter. On the other hand, with wellpurified activated-sludge effluentswhich have been subjected to aeration for about 20 hours, the carbonaceous oxidation deals with merely a small fraction of the organic matter remaining after the purification. With river-water samples the fraction is larger but still small, and its low value is undoubtedly due t o a portion of the water, having undergone considerable self-purification as evidenced by the presence of 0.3 to 0.8 p. p. m. of nitrate nitrogen in the samples. Table 11-Ratio of La to D i c h r o m a t e Absorption TYPEOF LIQUID AVERAGEMAXIMUMMINIMUU Raw sewage 0.72 0.88 0.49 Raw sewage centrifuged 0.88 1.05 0.74 Activated-sludge effluent 0.15 0.20 0.08 River water (containing 0.3 to 0.8 p. p. m. nitrate N) 0.25 0.46 0.14
The organic matter unaccounted for in La is probably responsible for the slow absorption of oxygen on incubation for prolonged periods. Comparison of Acid Dichromate and Oxy-Albuminoid Absorptions
Johnson5 has recently proposed to determine the carbonaceous matter by estimating the loss of permanganate on refluxing a sample under standard conditions for half an hour with a measured amount of alkaline permanganate. He claims that this “oxy-albuminoid test” records absorptions of about four-fifths the biological absorption. From Table I11 it is apparent that the oxy-albuminoid absorption is often considerably less than the dichromate absorption. Increase in the amount of sodium hydroxide or the period of refluxing did not materially increase the absorption recorded in the oxy-albuminoid test. No attempt has yet been made in this laboratory to compare the figures recorded by the new method with the biological demand as expressed by La. It is hardly t o be expected, however, that the test will distinguish between readily fermentable and stable carbonaceous matter, since the oxidation is carried out under the severe conditions of boiling with alkaline permanganate. of Acid D i c h r o m a t e a n d Oxygen-Albuminoid Absorptions OXYACID ALBUMINOID DICHROMATE RATIO SAMPLE (1) (2) (1):(2) P. p . m. P. p . m. Raw sewage 224 375 1.67 Raw sewage 166 244 1.47 Raw sewage settled 110 167 1.52 Raw sewage centrifuged 74.6 92.2 1.24 Activated-sludge effluent 34 36 1.06 Creek sample 41 43 1.05 Creek sample 14.5 20.6 1.42
T a b l e 111-Comparison
Acknowledgment
The author is indebted to the Shanghai Municipal Couneil for permission to publish the results of this investigation, 6
A T Z U sa, ~ , 130 (1927).
Discussion of Results
Table I1 summarizes the experimental results and shows that La may be very much smaller than the dichromate absorption. Since the dichromate absorption does not 4 Streeter and Phelps, U.S. Pub. Health Service, Pub. Health Bull. 146, p. 7; Theriault, Pub. Health Repts., 41,No. 6,p. 212.
Russian Chemical Production During the last quarter of 1927, the production of mineral acids in Russia reached 68,000 tons; calcined soda, 48,700 tons; caustic soda, 13,300 tons; and superphosphates, 35,500 tons (production curtailed because of insufficient supply of sulfuric acid).
