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T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
Certain factories can often meet viscosity and jelly requirements of a sample, b u t their glues will lack t h e strength and flexibility of glues from other factories having exactly the same jelly and viscosity. At t h e present time work is being done t o determine t h e following: I-The relationship between t h e viscosity, jelly strength, tensile strength, and stretch. a--The relationship between gelatin, chondrin, keratin, mucin, etc., and their effect on t h e strength and stretch of a glue. 3-Effect of heating and t h e length of time of heating on t h e strength and stretch of glues, both in liquid form and dried form. 4-Effect oE t h e soaking of glues on their strength a n d stretch. j-Effect of the age of glues on their strength and stretch. 6-Effect of dissolving a glue, drying, redissolving, etc., on the strength and stretch. 7-Effect of t h e addition of other substances to glue. 8-Effect of humidity and temperature on glue.
THE DETERMINATION OF IODIDE AND BROMIDE IN MINERAL WATERS AND BRINES’ By W. F. Baughman and W. W. Skinner B U R ~ AOFU CHEMISTRY, DEPARTMENT OF AGRICULTURE, WASHINGTON, D. C
I n a former paperZ t h e authors recommended t h e permanganate method for t h e determination of iodide in mineral waters and brines. By t h e use of this method t h e iodide is oxidized t o iodate by potassium permanganate in slightly alkaline solution and t h e iodate determined iodometrically b y adding potassium iodide, acidifying with hydrochloric acid and titrating t h e liberated iodine with thiosulfate. This method gives very satisfactory results for t h e iodide content, b u t i t does not leave t h e solution in a condition suitable for t h e determination of t h e bromide content. I n t h a t paper t h e authors also showed t h a t iodide may be quantitatively separated from large amounts of chlorides (up t o I O g. NaC1) and from amounts of bromide equivalent t o not more t h a n 0.3 t o 0.4 g. bromine by liberating t h e iodine with ferric sulfate and removing i t by distillation with steam. The iodine is absorbed in a potassium iodide solution and titrated with thiosulfate. I n a second paper3 a method was proposed for t h e estimation of bromide in t h e presence of large amounts of chloride ( I O g. NaC1). This method takes advantage of t h e selective oxidizing action of chromic acid, and t h e liberated bromine is removed b y aspiration. I n t h e present paper some results are reported of determinations of t h e iodide and bromide content of mixtures of iodide, bromide, and chloride. These 1 Read before t h e Division of Water, Sewage a n d Sanitation, a t the 58th Meeting of t h e American Chemical Society, Philadelphia, Pa.. September 5 , 1919. 2 THISJOURNAL, 11 (1919), 563. 2 I b z d . , 11 (1919), 954.
Vol.
12,
No. 4
results were obtained b y combining t h e ferric sulfate method for iodide with t h e chromic acid method for bromide. PROCEDURE
The procedure for t h e determination of iodide and bromide in the presence of chloride is a s follows: The iodide should first be determined by t h e permanganate method, since more accurate results can be obtained by its use t h a n by t h e use of t h e ferric sulfate method. Another sample is t h e n taken which should contain not more t h a n 0.1g. of bromine as bromide or more t h a n I O g. of total salts. T h e iodine is removed from this sample b y oxidizing with ferric sulfate and distilling t h e liberated iodine with steam according t o t h e method described in t h e first paper. T h e iodine is absorbed in a potassium iodide solution and may be titrated with thiosulfate and t h e results used t o check those obtained b y t h e permanganate method. The residue in the distilling flask is emptied into a beaker, heated t o boiling, and t h e iron precipitated with ammonia or sodium hydroxide, If sodium hydroxide is used, care must be taken n o t t o add a great excess, though a slight excess will be taken care of later by t h e chromic acid. Any excess of ammonia will be removed during t h e subsequent evaporation. Filter off t h e iron hydroxide, wash with hot water, and evaporate t o dryness or nearly so. The bromide is determined in t h e residue by t h e chromic acid method, t h e details of which were given in t h e second paper. Calcium chloride does not interfere with either determination, b u t care should be taken when precipitating t h e iron not t o precipitate too much calcium hydroxide b y t h e addition of an excess of alkali, as otherwise t h e precipitate will be bulky a n d difficult t o wash. This applies also t o magnesium chloride if sodium hydroxide is used for precipitating t h e iron. If much magnesium chloride is present t h e solution may become acid during evaporation, due t o hydrolysis. This may be guarded against b y coloring t h e solution with methyl orange a n d adding a drop of sodium hydroxide solution if i t becomes acid. Br as NaCl I a s KI Taken Taken
EXPThTo. G. 1 2 3 4
10
5
10
..
6 7 8 9 10 I1 12
13% 14
8’
10 10 10 10 10 10 10 10 10
.
G.
.... ....
0.0803 0.0803 0.0803 0.0402 0.0803 0.0803 0.0803 0.0803 0.0803 0.0803 0.0402
KBr
I
Br
Taken
Found G.
Found
G. 0.0600 0.0800 0.0800 0.0800 0.0200 0.0400 0.0800 0.0800 0.0200 0.0400 0.0020 0.0040 0.0010 0.1000
.. .. .. .. ....
0.0794 0.0792 0.0794 0.0397 0.0792 0.0795 0.0798 0.0805 0.0798 0.0792 0,0396
Error in I Det.
G. 0.0598 0.0798 0.0790 0.0798 0.0191 0.0385 0.0784 0.0790 0.0188 0.0385
G.
.... -0.0011 -0: 0009
-0.0009 -0.0005 -0.0011 -0.0008 -0.0005 0.0015 0.0002 0,0033 -0.0005 0,0006 -0.0011 0,0984 -0.0006
+
Error in Br Det.
G. -0.0002
-0.0010 -0.0002 -n on09 -0,0015, -0.0016 -0.0010 -0.0012 -0.0015 -0.0005 -0.0007 -0.0004
-0.0016
An inspection of the table will show t h a t t h e results for iodide are all low with t h e exception of Expt. 11, which is probably due t o an error of manipulation. Much better results can be obtained by the use of t h e permanganate method. The results for bromide are also low, b u t i t is believed t h a t this method will give more accurate results for t h e bromide content of such mixtures t h a n any other method.
