ANALYTICAL EDITION
272
be either a metastable phase or a phase which is stable in such a narrow range of composition that it is missed in the usual method of analysis when the system is allowed to come to equilibrium. The results at least indicate that it is not safe t o draw too close an analogy between the equilibrium diagram and a metallic system not in equilibrium, a condition so often found in practice; and they also suggest that there may be many interesting aspects of alloys not in equilibrium which have been missed in working out the niany metallic systems under equilibrium conditions.
1'01. 2,
so. 3
Literature Cited (1) Bablik, .S/nhZ Eisen, 44, 223 11924).
(2) Bablik, M e t a l I n d . ( L o n d o n ) , 26, 481 (1925). ( 3 ) Bradley and Thewlis, Proc. R o y . SOL. ( L o n d o n ) , Al22, 678 (1926). (4) Davey, Gett. EZec. Rev., 28, 586 (1923). ( 5 ) Finkeldey, Proc. Am. SOL.T e s t i n g Materials, 26, Pt. 2, 304 (1926). (6) Hull, Phys. Reo., 17, 571 (1921). (7) International Critical Tables, Val. I, p. 340, McGraw-Hill, 1926. (8) Osawa and Ogawa, Z . Kris:., 68, 177 (1928). (9) Rawdon, Proc. A m . SOL.Tesling Materials, 18, Pt. I , App. I11 (1918). (10) Westgren and Phragrnen, Phil. Mag.. SO, 311 (1925).
Determination of Perchlorate' H. H. Willard and J. J. Thompson UNIVFRSITY OF MICHIGAX, ANN ARBOR,~ I I C H .
T
HE usual methods of determining perchlorate involve reduction to chloride either by fusion or by means of
titanous sulfate. The latter may be used as a standard reducing agent or simply as a means of forming chloride. A review of various methods is given by Lamb and Marden ( 1 ) . Senften ( 2 ) has described a method differing entirely in principle, in which the perchlorate is mixed with potassium dichromate and concentrated sulfuric acid aiid gently heated to boiling. The gas is absorbed in a saturated solution of sulfur dioxide and reduced to c h l o r i d e . Although no explanation is given. the reaction seeins to be as foll o m : Upon h e a t i n g the solution of dichroiiiate and sulfuric acid the c h r o m i u i i i is red u c e d ; the hot perchloric acid o x i d i z e s i t a n d is r e d u c e d t o chloride. Soiiie qerious disadvantages are the formation of insoluble anhydrous chromic wlfate, causing bumping, arid the loss of perchloric acid due to yolatilization before reaction with c h r o m i u m t a k e s place. T h i s method Fvas carefully tested. but the results were low. Antimonous Figure 1-Apparatus for Determining and arsenious o x i d e s Small Quantities of Perchlorate were then tried as reducing agents in concentrated sulfuric acid, but somewhat low results were obtained. I n recent work on the determination of halogens in organic coinpounds (.?), potassium persulfate was eriiployed to facilitate the decomposition of carbonaceous material. Sonie samples of persulfate were found to be contaminated with perchlorate to so great a n extent that a blank had to be run to determine the chlorine present in this form. This suggested the application of this method to the determination of per chlorate.
1
Received March 22, 1930.
Experimental
It was found that if perchlorate is heated Fvith starch and sulfuric acid under proper conditions, it is completely reduced, mainly t'o chlorine, Tyhich is absorbed and reduced to chloride in alkaline arsenite solution and determined in the usual way. The potassium perchlorate, made from very pure materials, was further purified by recrystallization, aiid dried at 300" C. for 15 minutes ( 3 ) . TKOdeterminations mere made with the apparatus already described (5), using the following procedure: The weighed sample of approximately 1 gram, 0.8 gram of chlorine-free starch, and a few glass beads are placed in the flask. The apparatus is connected, having 1 gram of arsenious oxide in 100 cc. of a 10 per cent chlorine-free sodium hydroxide solution in the absorption flask. Sole--All joints are well lubricated with a viscous paste made by mixing phosphorus pentoxide with warm, sirupy phosphoric acid ( 4 ) . R u b b e r bands are used on the glass hooks.
Through the dropping funnel 35 cc. of concentrated sulfuric acid are added and the solution is brought t o the boiling point in 20 minutes. It is boiled 5 minutes, then 25 cc. of fuming sulfuric acid containing 20 per cent SO3 are added and the boiling is continued for 10 minutes. An excess of a saturated solution of permanganate is slowly added t o the boiling solution to espel any ch!orine remaining in the flask as hydrochloric acid. T h e water is drained from the condenser and the solution boiled 3 minutes. The solution in the absorption flask is transferred to a beaker and acidified with dilute nitric acid, using methyl orange as indicator. Excess of silver nitrate is added to precipitate the chloride, then 2 ce. of concentrated acid. The precipitate is filtered on a Gooeh crucible, washed with water containing a few drops of nitric acid, and then with acetone, dried at 135' C., and weighed.
The results are shown in Table I. It is desirable to work with a smaller apparatus; therefore one was designed as illustrated in Figure 1. This apparatus was satisfactory for samples \-arying in weight from 0.03 to 0.4 gram. K i t h samples of approximately 0.03 gram the amounts of reagents used were: 0.03 gram starch, 0.05 grain arsenious oxide, 15 cc. of a 10 per cent solution of sodiuin hydroxide, 6 cc. of 95 per cent sulfuric acid, and 3 cc. of funling sulfuric containing 20 per cent sulfur trioxide. K i t h a 0.4-gram sample the amounts Tvere: starch, 0.25 graIn; arsenious oxide 0.25 gram; 95 per cent sulfuric acid, 20 CC.; fuming sulfuric acid, 5 cc. The time required for a complete analysis was 45 minutes. The results of these analyses are shown in Table I.
ISDUSTRIAL A S D E S G I S E E R I S G CHEMISTRY
July 15, 1930
Table I-Analysis of Perchlorate CHLORISE CHLORISE TVT. KClOr FOUSD W T . KC104 FOCIND Grams Pe7 cent 1 P686a 25 55 1 3113 25 5s 0 1209 25.55 0 205s 25 55 0 2120 25.54 a The first two tests were made with the larger a p p a r a t u s , and t h e others with t h e smaller apparatus. b 0.5 gram K S O j added to KClO4.
Further experiments were made, varying the relative proportions of concentrated and fuming sulfuric acid. It was found that if 100 per cent sulfuric acid was added to the dry salt low results were always obtained, due probably to the formation of anhydrous perchloric acid which volatilized before reacting with the carbon of the starch. This volatilization appeared to take place even when the starch was added already carbonized. If only concentrated sulfuric acid was used, the perchloric acid was not entirely decomposed, because of the formation of water by the decomposition of the starch. This is readily remedied by the addition of fuming sulfuric acid. If just enough fuming sulfuric acid is added at the end of the reaction to make the acid 100 per cent, all the perchloric acid is decomposed and a n excess does no harm. Having this in mind, a n analysis was made of a 0.2-gram sample of potassium perchlorate, using 0.15 gram of starch added to the dry perchlorate. Through the dropping funnel 15 cc. of 95 per cent sulfuric acid were added and then brought to the boiling point in 15 minutes. I t was boiled for 1 minute, then 2 cc. of fuming sulfuric acid containing 20 per cent SO,
273
were added and boiled 5 minutes. An excess of Permanganate was necessary to expel the last traces of chlorine. The analysis was completed as described above and the results were good. This method was equally satisfactory when the perchlorate was mixed with a much larger amount of nitrate or persulfate. Determination of Chlorate, Bromate, and Iodate
These determinations were carried out by treating the salts with concentrated sulfuric acid using hydrazine sulfate as the reducing agent. With chlorate and bromate, permanganate was then added to expel the halogen from the flask, but with iodate it was necessary to use hydrogen peroxide because permanganate oxidized some iodine to iodic acid. The results are shown in Table 11. of Chlorate, Bromate, and Iodate
Table 11-Analysis SL-BSTWCE AIALYZED \%'IT
SAMPLE
KC103
0.155s 0.1229 0.1955 0 2748 0 1837 0.1036 0.1086
KBrOj
KIOa
HALOGEN
Theory
Gram
Per cent 28.93 4 7 , s5 59.30
Found Per cent 28.86 28.86 28.90 47.77 47.79 59.24 59.22
Literature Cited Lamb and Marden, J . .Am. Chem. SOL.,34, 812 (1912) Senften, Z . ges. Schiess- Sprenpsloifz,., l a , 17 (1917). Smith, J. A m .Chem. Soc., 47, 774 (1925). Stephens, Ibid.,52, 635 (1930). ( 5 ) Thompson and Oakdale, I b i d . , 52, 1195 (1930).
(1) (2) (3) (4)
Volumetric Determination of Tartrates' P. H. Richert FRCITP R O D U C T S LABORATORY, UNIVERSITY
I
S STUDIES of the solubility of various tartrates it became
necessary to devise a rapid and reasonably accurate method of determining total dissolved tartrates. Tartrate ion can he completely oxidized by permanganate under certain conditions. Unlike the oxidation of oxalate, the tartrate oxidation cannot be conducted satisfactorily with acid permanganate solution, because of the slow reaction in bhe last stages of oxidation and loss of material t'hrough volat,ilization of intermediate oxidation products. By the use of alkaline permanganate, hoivever, and heating for some time, these difficulties map be overcome and the results d l then be dependable. Saturally the method caiinot be used if other organic material or substances which reduce permanganate are present, such as would be found in fruit juices, etc. This method has been found useful in determining sinal1 quantities of tartrates such as are encount'ered in the determination of the solubilities of slightly soluble tartrates in the presence of inorganic salts. The following procedure has been found satisfactory for quantities of tart'rates u p to 30 mg. of tartrate expressed as tartaric acid: From a sample containing not more than 30 mg. of tartaric acid in 30 cc., pipet 53 cc. of solution int'o a 250-cc. beaker, add 10 cc. of 20 per cent sodium hydroxide solution and 25 cc. of 0.1 potassium permanganate, cover with a watch glass, and heat on hot plate for one-half hour, adding distilled water if necessary to keep the volume above 100 cc. Remove from the hot plate, cool slightly (to about 90" C.), add 10 cc. of 30 per cent sulfuric acid, and determine excess of permanganate with 0.1 N potassium oxalate, adding a slight excess of 1
Received January 20, 1930.
OF CALIFORTI%,
BERKELEY,C A L I F .
oxalate and titrating back with 0.1 S permanganate to a faint pink. If the alkaline oxidation has not been complete, this pink color fades in a short time, indicating that a longer period of heating on the hot plate should be used. Ten oxidation equiralenta are necessary to oxidize 1 mol of tartaric acid completely; hence 1 cc. of 0.1 N potassium permanganate is equivalent to 0.00130 gram of tartaric acid. The following table shows the results of analyses of known solutions of tartaric acid. The solutions mere checked by titration with standard sodium hydroxide solution. Chemically pure tartaric acid Tvas dried in a desiccator and 12.020 grams of this mere diluted to 1000 cc. making an 0.0801 molar solution as determined by titration with 0.1 N sodium hydroxide. This solution was diluted to one-twentieth for the tartrate determination with permanganate as described above. 0 . 1 .V KMnOi F O R 50 CC.
TARTRATE SOLN.
KMnOa 25 CC.
r51NG
TARTRATE SOLN.
cc CC 20 06 10 05 20 0 s 10 09 20 0 s 10 07 20 09 10 07 20 12 10 12 20 05 10 09 20 11 THEORETICAL EQUIVALENT 20 02 10 01
BLANKO N
EKTIRE
PROCESS Cc. K WnOl 0 06 0 os 0 10 0 02
BL.ASKO N REAGENTS N O T BOILED
cc. 0 0 0 0
00
00 00 00
The high results apparently are caused by the reaction of the permanganate with something besides the tartrate, possibly the glass beaker in which the alkaline solution is heated. However, the results are within 0.2 mg., which is sufficiently accurate for many purposes.
