IAVDC;STRIALA N D E-VGINEERISC: CHEMISTRE'
June, 1928
Concentration Factor
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S t o c k solutions of varying basicity were prepared and the effect of dilution of each of these stock solutions was d e termined in a series of experiments. I n all cases the tanresults, ning period summarized was 24 hours. in Figure The 2, show that the greatest degree of fixation is obtained from the most dilute solutions employed,
INDUSTRIAL A N D ENGINEERING CHEMISTRY
634
oxide, resulting from removal of sufficient ferric sulfate to dilute the remaining solution to such a degree as to cause precipitation. The amounts of iron fixed by hide powder from solutions at (OH)-/Fef++ = 0.160 are practically twice those from solutions of basicity = 0, 100 grams hide substance combining with 7.0 grams Fer03 from the basic solution and with 3.35 grams from the solution of the normal salt. Taking
gave unreliable results owing to precipitation of hydrous ferric oxide by the added salt and are not included here. With solutions of the normal ferric salt concentrations up to 5 M sodium chloride and 0.75 M sodium sulfate could be employed. With the basic salt, concentrations were limited to 2 M sodium chloride and 0.75 M sodium sulfate. The desired weight of salt was added to 450 cc. of the ferric sulfate solution and agitated until completely dis-
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Figure &Effect of Presence of Neutral Salt AII solutions were clear and free from precipitate.
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Vol. 20, No. 6
for 24 hours, using 400 cc. tanning solution and 2 grams of hide powder, as before. The results are summarized in Figure 4. It is to be noted that in all cases the presence of increasing a m o u n t s of sodium chloride causes, progressively, a decrease in fixation of iron from solution. The results with sodium sulfate are unusual, in that this Salt gives less r e t a r d a t io n t h a n
Availability of Nitrate Oxygen in Filter Effluents' 0.M. Urbain URBAIN& HUNT,COLUMBUS, OHIO
URING the writer's experience in testing filter effluents he has observed some outstanding peculiarities. I n determining the biochemical oxygen demand by a method involving a combination of the dilution and the nitrate methods, the nitrate oxygen is not available until after the dissolved oxygen has been consumed. Furthermore, the rate of consumption of the nitrate oxygen is much slower than that of the dissolved oxygen. These observations have led to the conclusion that nitrate oxygen in filter effluents is available only under anaerobic conditions and that nitrate oxygen does not add to the oxygen balance of waters receiving filter effluents. To substantiate these observations, experiments were made on various filter effluents as well as raw untreated sewage; in each case the results were the same, and in no case was the nitrate oxygen available until after the dissolved oxygen had been consumed.
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Experimental Methods Used
The standard methods of the American Public Health Association were used in determining the dissolved oxygen, nitrites, and nitrates. The counts for aerobic bacteria were made on plain agar incubated a t 20" C. for 48 hours. The anaerobic counts were made on plain agar in a vacuum. A 1
Received January 31, 1928.
dish of potassium pyrogallate was used on top of the inverted Petri dishes to take up the last traces of oxygen remaining after evacuation. The anaerobic counts were also for 48 hours a t 20" C . I n preparing the dilutions the standard 250-cc. glass-stoppered bottles were used. The exact volume of each bottle was determined and all other factors were carefully controlled. Preparation of Dilution Water
A very pure water that had been specially aerated was used for the dilutions. The quality of this water was important because on its purity depended the accuracy of the final results. This water was prepared about 30 days before use according to the following scheme: To a quantity of distilled water was added c. P. sodium nitrate equivalent to approximately 10 p. p. m. of nitrate nitrogen, which was in turn equivalent to 28.5 p. p. m. of nitrate oxygen. Air was then bubbled through the water for 12 hours to saturate it with dissolved oxygen. This air was passed through concentrated sulfuric acid to remove any ammonia fumes or bacteria it might have contained. A sulfuric acid trap was also attached to the container and the water stored for 30 days. This was thought to correct any supersaturation conditions and the water was assumed to have a normal dissolved oxygen content at the laboratory temperature following this treatment. The
