July 15, 1942
ANALYTICAL EDITION
TABLEV. STORAGE TESTSWITH RESIN-LINED CASS Silica as Si01
Type of Sample
P. p . Distilled water Distilled water saturated with carbon dioxide
0.0
.. .. *.
Sulfuric acid, 0.02 N Alkaline boiler water added to can a t 23' C. Philadelphia t a p water (Delaware supply) added to can at 95' C.
m.
0.0 0.0 0.0 0.0 0.0
29.7 29.5 28.7 4.0 4.1 4.0
Total Iron as F e
Date of Analysis
P. p . m. 0.0 0.0 0.1 0.0 0.0
0.1 0.0 15.0 1.0 0.2 0.2 2.0 0.1 0.1 0.1
5/3/40 6/3/40 6/3/41 5/3/40 6/3/40 6/3/41 5/2/40
571
Hard-rubber bottles and resin-lined cans provide excellent containers for sampling and storage of water samples. I n the handling of large numbers of water samples for silica determinations, the authors have found resin-lined cans economical and convenient.
Summary Appreciable increase in the silica content of water samples may result from the use of glass bottles for sampling and for storage. This increase in silica is more marked with alkaline water, such as boiler water, than with raw water, feed water, and condensate. The increase in silica is also greater if the sample is placed in a bottle hot than if it is first cooled to room temperature. Silica pickup from Pyrex containers has been noted, although not to the extent experienced with ordinary soda glass. The use of steel drums or tin-lined cans results in a corrosive &ion on the metal, precipitation of iron, and the lowering Of the 'Ontent Of the water The use Of hardrubber bottles or resin-lined cans prevents any change in the silica content of the water within limits of analytical error.
:$:$:: 5/3/40 6/3/40 6/3/41 5/3/40 6/3/40 6/3/41
the other case, the resin-lined cans showed a silica result of 5.6 against 2.3 p. p. m. in the sample shipped in the drum. Considerable corrosion of the steel drums was evidenced, together with precipitation of iron. Samples were received in the laboratory 3 days after they had been taken and the analyses were completed on the fourth day after sampling. In another case, a sample of water was forwarded t o the laboraAcknowledgment tory in two containers, one ordinary soda glass and the other a resin-lined can. The sample secured in glass showed a silica conThe authors wish to express their appreciation to tent of 15.5 p. p. m. as Si02,whereas the sample in the resin-lined can showed silica as 7.2 p. p. m. samples were secured january & L. D. Betz, in Those laboratories this investigation was conducted. They are also indebted to the American Can 17, 1941, and analyzed February 6. Company for the resin-lined containers used in the various The resin-lined can employed was a tin plate container, tests, carrying two interior coats of organic protective coatings. The undercoat is a high baked cured modified alkyd resin Literature Cited varnish. The top coat is a baked vinyl chloride-vinyl acetate (1) Am. Pub. Health Assoc., "Standard Methods of Water Analysis", copolymer spirit varnish. This container is the standard beer 8th ed., p. 91, 1936. package manufactured by the American Can Company. (2) Belyea, A. R., and Moody, A. H., Proc. Am. SOC. Testing
'"
Conclusions I n making recommendations for the removal of silica from water, designing feed water conditioning systems, setting silica limits for a boiler water, and determining the solids content of condensed it is not safe to assume that the increase in silica from a glass container will be negligible. It is essential to secure water samples in containers that will not impart silica to the sample and to use containers that will not rust and so reduce the silica content of the water sample.
Materials, 41, 1264 (1941). (3) Collins, W. D., and Riffinburg, H. B., IND. ENG.CHEX.,15,48-9 I * no"\
\lY.&SJ).
(4) Kahler. H. L., IND.ENQ.CHEM.,ANAL.ED., 13,536 (1941).
(5) Schwartz, M. C. (discussion of paper by F. G. Straub and T.A. Bradbury), Mech. Eng., 61,146 (1939). (6) Ulmer, R. C., Proc. Am. SOC.Testing Materials, 39, 1221 (1939). (7) Wichers, E., Finn, A. N., and Clabaugh, W. S., IND.ENQ.CHEM., ANAL.ED., 13,419 (1941). PRESENTED before the Division of Water, Sewage, and Sanitation Chemistry a t the 102nd Meeting of the ~ \ I E R I C A N CEEMICAL SOCIETY, Atlantic City, N
J.
Fluorescein As an Indicator in Bromometric Titrations F. L. HAHN, Casilla 221, Quito, Ecuador
T
HE use of methyl orange or methyl red in bromometric titrations involves the inconvenience that the indicator may be destroyed by a local or temporary excess of free bromine before the equivalence point is reached. Fluorescein, a highly sensitive reagent for bromate in the presence of bromide ( I ) , permits one to observe the approach and the passing of the end point. The indicator solution may be prepared by dissolving 0.1 gram of fluorescein in 100 ml. of water containing some drops of sodium hydroxide. One drop of indicator is added to each 10 ml. of titrated solution. In a bromometric titration of arsenious acid (strongly acidified 1%-ithhydrochloric or sulfuric acid) the greenish yellow of the solution changes to a brownish ye1loTv when the end point is approached. The change to a reddish brown indicates the end point. As the fluorescein reacts only slowly
with bromine, it is necessary, near the end point, to wait some 15 seconds after each addition of reagent. Heating the solution to 40' to 50' C. will accelerate the reaction. -4 permanganate solution (approximately 0.1 N ) and a bromate solution (approximately 0.05 N plus 20 grams of potassium bromide per liter) were compared iodometrically. Then the arsenite solution was titrated with permanganate, using a little iodide as a catalyst, and with bromate solution. The results mere' 1 ml. of KMnO, = 1.855 ml. of KBrOa (iodometrically) = 1.833 mi. of KBrOs (with fluorescein)
Literature Cited (1) Hahn, F. L., Mikrochemie. 20, 236 (1936).
