August 15,
1941
Literature Cited Bertrand, Bull. SOC. chim. biol., 6, 157 (1924). Dienert and Wandenbulke, Compt. rend., 176, 1478 (1923). Foulger, J . Am. Chem. SOC.,49,431 (1927). Isaacs, Bull. SOC. chim. biol., 6, 157 (1924). Jolles and Neurath, Z.angew. Chem., 11, 315 (1898). Mellon, IND. ENQ.CHEM.,l n a l . Ed., 11, 80 (1939). Muller, Ibid., 11, 1 (1939),
(1) (2) (3) (4) (5) (6) (7)
539
ANALYTICAL EDITION
(8) Munro, Proc. Trans. Nova Scotian Inst. Sci., 16, 9 (1928). (9) Schwartz, IND. ENG.CHEM.,Anal. E d . , 6, 364 (1934). (10) Snell, "Colorimetric Methods of Analysis", New York, D. Van Nostrand Co., 1936-37. (11) Summerson, J . Biol. Chem., 130, 149 (1939). (12) Thayer, IND.ENQ.CHEM.,Anal. Ed., 2, 276 (1930).
PRESENTED before t h e Division of Water, Sewage, a n d Sanitation Chemistry a t t h e 100th Meeting of t h e American Chemical Society, Detroit, Mich
Anhydrous Sodium Thiosulfate, A Primary Standard HAZEL SI. T03ILINSON
AVI
FRANK G. CIAPETTA, Temple University, Philadelphia, Penna.
T
HE reaction between bromoacetate and thiosulfate ions
has been found b y Slator ( 8 ) and by La Mer and his coworkers (4, 5, 6, 9) to be uniquely free of side reactions. Accordingly, the measurement of velocity constants using these reactants offers a critical method of detecting the existence of decomposition products of either reagent. By employing such kinetic measurements, Kamner and Tomlinson working with La Mer (6, 7 ) have shown that the pentahydrate of sodium thiosulfate decomposes upon standing a t room temperature for several months after recrystallization. At the suggestion of La hIer, the investigation has been extended to include t h e stability of the anhydrous salt. I n 1904, Young (IO) suggested the use of the anhydrous salt a s a primary standard but presented only meager supporting data. This paper shows that anhydrous sodium thiosulfate is stable thermally at 120" C. and meets the requirements of a primary standard so well t h a t it deserves more extended use. The methods of purification of reagents and the technique of reaction velocity measurements were those of La Mer and ' in reactants were employed. Kamner. K a t e r solutions 0.01 h After two kinetic determinations, sodium thiosulfate pentahydrate was placed in a n oven a t 120" C. Portions of the dehydrated product were used for subsequent reaction rate measurements. The data in Table I show conclusively that this thiosulfate was not decomposed by the heat to which i t was subjected over a period of 11 veeks. The drifts in velocity constants noted by La Mer and Tomlinson using the pentahydrate which had been kept a t room temperature for 2 years were not' observed. Samgles of c. P. sodium thiosulfate pentahydrate were dried a t 120 C. to constant mass and stored over calcium chloride. Portions of these samples were recrystallized from water belon65" and then subjected to dehydration to ascertain the importance of recrystallization. The time required for dehydration depends, of course, upon the frequency of stirring the solution formed upon heating the hydrated salt and later upon the frequency and degree of subdivision. Individual samples of the thiosulfate (0.2 to 0.4 gram) were titrated with 40 to 50 ml. of standard iodine solutions using calibrated volumetric apparatus; the iodine purification, solution preparation, and titrations were carried out after the method of Kamner ( 3 ) . c. P. resublimed io-. dine was sublimed from a 1 to 5 potassium iodide mixture and this product was sublimed again, dried, and stored over calcium chloride. All iodine solutions contained 4 per cent of potassium iodide. Freshly prepared solutions of soluble starch (0.5 per cent) were used and correction blanks determined. From Table 11, i t may be seen that the concentrations of iodine solutions determined against weighed portions of these anhydrous samples and the values calculated from the masses
of iodine used are in good agreement, even when the c. P. grade salts were employed without recrystallization. The analysis of the dehydrated, unrecrystallized sample 2 indicated that it was slightly decomposed. This was confirmed b y kinetic measurements upon both dehydrated and original samples. The velocity constants so obtained exhibited pronounced drifts which corresponded to those observed in previous investigations. When an accuracy greater than 2 parts per thousand is not obligatory, the data indicate that the c. P. salt of commerce may not require recrystallization. Upon recrystallization, the results are in agreement well within the limit of experimental error. Arsenious oxide (99.82 per cent As203 us. Bureau of Standards Sample 83) was used to determine (1) independently the normalities of two standard iodine solutions prepared by weight. The excellent agreement between these iodine concentrations determined by arsenite and thiosulfate titrations is shown in Table 111. Moreover, it is evident from the precision obtained that no marked change had occurred in the composition of these anhydrous samples which had been stored in a bright laboratory, but seldom in direct sunlight,
TABLE I. EFFECT OF HEATIKG SODIUXTHIOSULF~TE (;is determined b y r a t e of reaction with sodium bromoacetate) D a y s K e p t a t 120' C . Velocity Constant, k 0 0 . 4 8 9 * 0.001 0 0.490 * 0.000 2 0 . 4 9 0 * 0.002 4 0.487 0.002 9 0.492 f 0.002 16 0.492 0.001 28 0 490 0.001 79 0 . 4 8 8 =t 0.001 f f
kav. = 0.490
* 0,001
I O D I K E SOLTsTIONs B Y SODIUM THIOSULFa4TE
TABLE 11. ANALYSESO F Sample
1 1 recrystallized 2 2 recrystallized 3 3 recrystallized 4 4 recrystallized
Sample a t 120' for
Normality b y NazSz03 0,05825 0.04045 0.05825 0.04045 0. 06825 0.05s25 0.05s25 0.05590a 0.058ljb 0.04255' 18 days, b 28 days,
Normality Calcd. from 1%Content 0.05828 0.04046 0.05839 0.04046 0.05832 0,05825 0.05822 0,05592 0,05825 0.04257 C
79 days.
Deviation
70 0.05 0.03 0.24
0.00 0.12 0.00 0.05 0.04 0.00 0.05
INDUSTRIAL AND ENGINEERING CHEMISTRY
540
TABLE 111. ANALYSESOF IODINE SOLUTIONS BY SODIUM TKIOSULFATE AA-D BY ARSENIOUSOXIDE NapStOj
Normality by
NatSzOs
Normality b y As202
h'ormality Calcd from 1 2 Content
1 recrystallized 2 recrystallized 3 recrvstallized 4 recrirstallized
0.04256 0.04323 0,04254 0.04322
0.04253 0.04319 0.04253 0.04319
0.04255 0.04320 0.04255 0.04320
Sample h o .
Iv. AXALYSESOF CERIC SULF4TE SOLUTIONS BY SODIUM THIOSULFATE AFTER PROLOKGED EXPOSURE TO LIGHT
TABLE
h-orinality by Sample 1 recrystallized 2 recrystallized 3 recrystallized
Ka&Os 0.04564
0,04572 0.04865
Sormality by RIohr's Salt 0.04562 0.04562 0.04562
Deviation
Vol. 13, No. 8
tion of sample 2 gained 48 mg. in 18 days but was redried completely in 1 hour a t 120".
Summar? The stability of anhydrous sodium thiosulfate has been investigated. No decomposition has been indicated by the critical method of reaction velocity measurements n-ith sodium bromoacetate when the salt was kept a t 120" C. for 79 days. The dehydration of sodium thiosulfate pentahydrate produces an anhydrous salt which fulfills the requirements of a primary standard.
7% 0.04 0.22 0.07
TABLE
POSITIOK OF
COU-
SODIUM THIOSCLFATE
(h-ormality of Ce(S0i): by Mohr's salt, 0.04562) S o r m a l i t y of Days Ce(SO4)t b y Deviation Sample Exposed NapSnOa 70 1 recrystallized 18 6.04561 0.02 24 0.04363 0.02 32 0.0437 0.11
for a month over calcium chloride. Further substantiation of this stability toward light, in the absence of moisture, is presented in Table IV. These samples were stored similarly for 11 months, then separate portions (0.25 to 0.35 gram) were titrated with ceric sulfate solution ( 2 ) .
31
0.04559 0.04562
3 recrystallized
21 34
0.04660 0.04564
0.07 0.00 0.04 0.04
5 recrystallized
0 23
0.04557 0.04562
0.11 0.00
2 recrystallized
I n order to determine the possibility of decomposition of anhydrous sodium thiosulfate exposed to both light and air, portions were exposed to the atmosphere of the laboratory in weighing bottles set in beakers covered with watch glasses. After known periods of exposure, the samples were heated at 120' C. to ronstant mass, and separate portions were titrated with the ceric sulfate previously employed. Typical resulting data appear in Table V. Obviously, detectable decomposition had not occurred. Finally, sodium thiosulfate was found to be not appreciably hygroscopic and readily redriable to constant mass. A portion of sample 5 which had taken on 1.6 per cent of its weight of water during 7 days' exposure to the air was dried to its original mass in 2 hours at 120". A portion of sample 1 with similar surface exposed showed no change in mass over a period of 6 days under similar conditions. A 4.503-gram por-
IT. EFFECT OF EXPOSURE TO LIGHTAND AIR UPON
19
Literature Cited (1) Chapin, J . Am. Chem. Soc., 41, 351 (1919).
Furman and Wallace, Ibid., 53, 1283 (1931). Kamner. dissertation. Columbia University, 1934. La Mer, J . Am. Chem. Soe., 51, 3341 (1929). La Mer and Fcssenden, Ibid., 54. 2351 (1932). La Mer and Kamner, Ibid., 57, 2662, 2669 (1935). L a Mer and Tomlinson, IND. ENG.CHEX.,Anal. E d . , 9, 588 (1937). (8) Slator, J . Chem. Soc., 87, 481 (1905). (9) Tomlinson, dissertation, Columbia University. 1939. (10) Young, J . Am. Chem. Soc., 26, 1028 (1904). (2) (3) (4) (5) (6) (7)
Quantitative Spectrochemical Method for Zinc Die Casting Analysis M. F. HASLER
AND
C. E. HARVEY, Applied Research Laboratories, Glendale, Calif.
T
HE literature of the last few years pertaining to spectrochemical analysis by means of the emission spectrum indicates clearly that a new era in speed, accuracy, and dependability of this type of analysis has been ushered in. The 10-minute analysis of steel for silicon, manganese, chromium, nickel, and molybdenum, with a n inaccuracy of less than 3 per cent of the quantity being measured in all cases, is a typical example ( 4 , 6 , 6 ) . These gains in speed, accuracy, and dependability have been achieved through no revolutionary innovations but rather through a realization of all the factors making for a good analysis. Apparatus designed m-ith these factors in mind is now available, so that any laboratory can be assured of definite results in connection with the analysis of certain materials. The extension of these contemporary methods to the analysis of a wide variety of materials is the immediate need in spectrochemistry. The development of a new modification of the standard direct current arc (1) by these laboratories has made possible rapid and accurate analyses of materials that have been analyzed heretofore by tedious spectrographic or chemical methods. The present paper describes the ap-
plication of this source and a standard group of instruments to the analysis of one such type of material, zinc die casting alloys. Since 1935 the American Society for Testing Materials has recommended a spectrochemical method ( 2 ) suitable for the analysis of lead, tin, cadmium, magnesium, iron, and copper in both zinc and zinc alloys such as are used in die casting. The method has enjoyed considerable popularity due to its inherent advantages when compared with routine chemical methods. These advantages are, in the main, connected with the spectrograph's ability to register lines of the various elements just as accurately a t very low concentrational levels as a t the higher levels. I n other words, the spectrograph allows a constant degree of accuracy nearly independent of the quantity of a n element present. For this reason errors in this analytical method are always referred to as a certain percentage of the quantity present, be that quantity 0.001 or 10 per cent. Many routine chemical methods, on the other hand, have a fixed absolute error expressed as a certain percentage of the entire sample and not dependent upon the amount being
