V O L U M E 23, NO. 9, S E P T E M B E R 1 9 5 1
1333
McComb (6)t o be stable and to contain the theoretical amount of water. However, Gladstone and Bruce ( 2 )report,ed sodium acetate as unsatisfact’ory, because commercial samples contained as much as 103.5% of the theoretical water content. D a t a in Tahles-I and I1 indicate that sodium acetate drfinitely does not meet the criteria st,ated above. Ammonium oxalate, ferrous ammonium sulfate, lactose, and oxalic acid, while they appear to be stable a t extreme humidities, frequently cont.ain appreciably more than the theoret,ical amount of water (Table I). T h e water content of lactose cannot be checked by heating because of its instabi1it.y even in a vacuum. Sodium bit’artrate frequently contains considerably less than the theoretical percentage of Tvater. Of all the substances t,ested, sodium tartrate proved to be outstanding. S o t only isit stable a t extreme humidities, b u t its \vat,er content is rmiarkably close to theory. A sample stored for 7 years in a screw-cap bottle without special precautions was found to contain substantially the theoretical wat,er content (Table l). As a n added advantage t h r water content, can be independently rhecked by he:ttine; a t 150 for 3 hours or to constant weight. Although it is relat,ively insoluble in ubsolut,e methanol, its n-ater content is rapidly and quantitat,ively titrat,able to a sharp end point. The authors have found reagent-grade small prismatic vrystals, up to a fen- millimeters in length, a convenient physical form. This subst,ance has been used routinely as a primary rtanda1.d in these 1aborat.ories for about 3 years n.it,h very satisS stveral t.housand determinations. factory I ~ P R U I ~in
‘Table I I .
Stabilit) of Crjstalline Hydrates a t I‘arious Hiimidi t ies Hours
Substance .Iluininuni potassium Sulfate A4mmoniumoxalate Citric acid Ferrous ammonium sulfate Lactose Oxalic acid Potassium citrate Sodium acetate Sodium tartrate Sodium citrate Siilfoaalicylie acid
% Gain i n Weight
posed
20%
31%
tit
‘0.04 -0 04 - 8 24
+0.03 +0.03 -0.25
fO.05 T O 06
-0.02 -0.04 71.26
497 497 283 191 191 191
-0
TO
-0 ‘0 -0 +O
-0 07 1 0 05
+O
144
283
-0 -0 4-0 -0 -0 -0
06
07 0.2 02 01 03
05
Residual Metal in Discharged Magnesium Batteries B. J. STURM Burgess Battery Co., Freeport, I l l .
T IS sometimes advantageous to know the quantity of unre-
I acted magnesium remaining in a discharged battery, in order to evaluate its performance fully. If all corrosion products and battery separator are removed from the electrode without attacking the free metal, the detc3rniination involves only weighing of the magnesium. Water is not suitable for removing corrosion products from magnesium, :is these compounds are not very soluble, and the electrode corrodes rapidly when wet because of the ions that are prescxrit. JIagnesium batteries usually contain halides or sulfates which arc: especially corrosive. Uhlig ( 1 ) reports that magnesium is attacked by all acids escept hydrofluoric and chromic. The presence of halide or sulfate ions, however, causes chromic acid to attack magnesium. Jlagnesium resists corrosion by hydrofluoric acid because a thin layer of insolubltx magnesium fluoride is formed on its surface.
Relative Humidity of: 65% 79%
io.02 +0.03 -8.30 02 05 - 0 03 L O 01 - 3 22 -0 04 -0 03 -0 08
RECEIVED December 27. 1950.
EXPERI\IEhTAL
51%
497 497 283
+o
(7) “Pharmacopeia of the United States of America,” 14th Revislon, pp. 795-7, Easton, Pa., Mack Publishing Co., 1950. (8) Rennie, R. P., and Monkman, J. L . . Can. Chem. Process I n d s . . 29,366 (1945). (9) Karren, G. G., I b i d . , 29, 370 (1945).
+o +o
06 08 01 03 02 04
+ 3 25
t0.32
- 0 02 +33 3 1 0 13 + o 01
-51
6
07 01 -0 03 C40 3 + 1 94 i o 09 A 5 40 -46 7
+o
Both the direct titration and the back-titration with standard water-in-methanol solution can be used. Standardization of Karl Fischer Solution Using Sodium Tartrate Dihydrate. Select a sample of reagent-grade sodium tartrate dihydrate small crystals, the water content of which has been established as 15.66 0.05% by heating a t 150” C. for 3 hours. A sample of 150 to 350 mg. 1~111require 5 t o 10 ml. of a solution whose strength is equivalent to about 5 mg. of water per In1. Titrate about 25 ml. of absolute methanol to the end point with the Karl Fischer solution. Quickly add the sodium tartrate and titrate again. Determine the weight of sodium tartrate by difference. This weight multiplied by 0.1566 and divided by the milliliters of Karl Fischer solution used gives the strength of the Karl Fischer solution in equivalent milligrams of water per milliliter.
*
LITERATURE CITED
Cornish, G. R., Plastics ( L o n d o n ) , 10, 99 (1946). Gladstone, T. P., and Bruce, T., .%NAL. CHEM.,19, 884 (1947). “International Critical Tables.” Tol. I, p. 67, New York, RIcGraw-Hill Book Co., 1926. Jones, G. K., PaintMfg., 15, 360 (1945). McComb, E. A.. ASAL. CHEM.,20, 1219 (1948). Mitchell, J., Jr., and Smith, D. M., “Aquametry,” p. 68, S e w York, Interscience Publishers, 1948.
The corrosive action on magnesium of the reagents used i n the determination was evaluated. Pieces of buffed magnesium 1.375 X 1 X 0.006 inch, weighing approximately 0.22 gram each, were immersed for 10 minutes in the liquids listed below, dipped in acetone, and dried. The change in w i g h t was noted. The balance used for the m eighingq had a sensibility of 0.0002 gram. Weight, ChangeGram of
Solution
207, aqueous hydrofluoric acid 20yo hydrofluoric acid with 5% niagnesiuin chloride 20% hydrofluoric acid with 3%. maanesiuni sulfate . Acetone
-0.0001 t 00..000 0 1 + -0
0002
These results shoii that 20% hydrofluoric acid does not react appreciably with magnesium mr,tal even in the presence of sulfate 01 chloride ions. Distilled watei a n d acetone do not react n i t h the metal appreciably during tho 10-minute immersion. T h e procedure described below is based on the above experiments, and has been used for analysis of both water-activated reservr batteries and dry batteries which use magnesium anodes. The determination represents elemental magnesium, when pur(’ magnesium electrodes arc used. PROCEDURE
Immediately after discharge the battery is dissected and the magnesium electrode stripped of any easily removed separator. The metal is placed in 20% hydrofluoric acid for 10 minutes, in a wax-coated beaker, and the solution is agitated with a coated stirring rod. T h e electrode is removed from the hydrofluoric acid, dipped in acetone, and allowed to d r y and its weight is determined. LITER4TURE CITED
(1) Uhlig, “Corrosion Handhook,” p. 225, Xew York, John n’iley & Sons, 1948. RECEIVED January
29, 1951.
