Analytical Reactions of Rubidium and Caesium WM. J. Q’LEARYAND JACOBPAPISH,Cornel1 University, Ithaca, N. Y.
T
HE close s i m i l a r i t y in
or rubidium (19); under condiA critical r&mL is given of the known anathe chemical behavior of tions described in detail below, lyticai methods for determining potassium, ruthis reagent affords a satisfacpotassium, r u b i d i u m , bidium, and caesium. A reaction of rubidium and and caesium has led to numertory separation of caesium from caesium is described that affords a satisfactory ous a t t e m p t s to separate one potassium and rubidium. from the other. I n most inseparation of these elements f r o m potassium. A Germanotungstic acid (6,54) stances the separations are only modification of the standard chloroplatinate prowas found to be less sensitive cedure is suggested, and a n improved method is toward rubidium and caesium partial, and can be used for t h a n t h e corresponding silico n o t h i n g more than a proposed for the quantitative separation and detive indication of the presence complex, but can be used for the of two or a l l t h r e e of t h e s e termination Of potassium, rubidium, and qualitative detection of these alkalies. A few attempts have sium, based on the use in succession of 9-phosalkalies in the presence of potasbeen satisfactory for the prepaphomolybdic, silicotungstic, and chloroplatinic sium. Attempts to form inration of c o m p o u n d s of t h e acids. soluble titanotungstates (36) pure i n d i v i d u a l rare alkalies, failed. but none of the methods so far The fluosilicates of potassium proposed is in any sense quantitative (98). (52) and rubidium (7)are too soluble for a quantitative separaAmong the reactions that have been used in alkali analysis tion from the corresponding caesium (48) salt; no solubility are the standard perchlorate and cobaltinitrite methods, which data were available for the fluotitanates (47) and fluotantaprecipitate all three alkalies without any separation. The lates, but investigation showed that they behaved like the same is true of the standard chloroplatinate method; Wer- fluosilicates. Potassium is the least soluble of the fluogernadski (67), however, claims a separation and determination manates (40, 68) and is too soluble for quantitative work. of rubidium in a feldspar by fractional precipitation of the Caesium and rubidium chlorostannate (9, 28, 39, 55, 69, chloroplatinates. Brauner (4) says that 22 per cent of any 60) are the compounds most often used in rare alkali analysis; lithium present is carried down as chloroplatinate with the they are not, however, quantitative except under conditions potassium. Jenzsch (33) states that lithium and potassium that cause an appreciable co-precipitation of the potassium form a mixed chloroplatinate. Smith and Shead (56) use compound. Caesium bromostannate (38, 49) is much more lithium chloroplatinate as a precipitant for potassium. insoluble than the chlorostannate, and the corresponding Robinson (61) removes most of the potassium from rubidium potassium salt is hard to prepare; on the other hand, rubidium and caesium by fractional precipitation with chloroplatinic bromostannate is considerably more soluble than the chloro acid and strong hydrochloric acid. It is evident from these compound; bromostannic acid consequently shows some statements that the analyst should ascertain the composition specificity toward caesium, but not sufficient to warrant its use of every final precipitate obtained from a mixture of alkalies in accurate work. The iodostannates (1) of rubidium and in order to be sure of what he is weighing, caesium are employed in microscopic qualitative analysis, but The alums have never had a wide use in quantitative alkali the authors found them much more soluble than the chloroanalysis because of their relatively high solubility, although, stannates, which makes them well suited for microscopic according to Browning and Spencer (5), they possess some analysis (11). advantages over the chloroplumbic and chloroantimonic acid The chloroplumbates (66) have been discarded even for methods. qualitative work; they are the least soluble of the lead halide Indirect analysis has long been employed (8, 12, 27) to complex salts. determine potassium, rubidium, and caesium; using mixReed and Withrow (60) claim that potassium alone precipitures of standard solutions of these alkalies, however, the tates as a double zirconium sulfate, while rubidium and caewriters found that an error of 0.1 mg. in weighing the platinum sium do not; on the other hand, Yajnik and Tandon (70) say from mixed chloroplatinates, or an error of 0.5 mg. in weighing that all three alkalies are quantitatively precipitated as zirsilver chloride from the mixed chloroplatinates, was multi- conium sulfate. Sodium bismuth thiosulfate (10, 30) precipitates all three plied by subsequent calculations as much as seventy fold, giving positive and negative deviations as high as 30 per cent of the alkalies, from the true values. Bunsen (8) urges caution in accepting It was found that rubidium and caesium bismuthinitrites the results obtained by indirect methods. (2) would precipitate only when moderately concentrated, Potassium, rubidium, and caesium phosphotungstate (38, and that the filtrates from such precipitations always yielded 46) are the most insoluble salts known of these alkalies but, a positive reaction with chloroplatinic acid; although the as in the case of the above-mentioned reactions, no separation bismuthinitrites afford a separation of rubidium and caesium from potassium, they are too soluble for quantitative work. is effected. Sodium silicomolybdate (31, 32, 38, 45) is a t present used Caesium bismuth iodide (66) is sufficiently insoluble to to separate rubidium and caesium from potassium; it is, recommend its use in microscopic analysis as a specific rehowever, by no means quantitative for caesium, much less for agent for caesium, but has never found a place in quantitative procedures; Tananaeff (62, 63), however, states that he rubidium, but serves for technical purposes. Silicotungstic acid (16, $2, 37) is a quantitative precipi- effects a quantitative separation of caesium from rubidium tant for caesium and does not ordinarily precipitate potassium by means of this reagent. 107
108
_.’ \
ANALYTICAL
Godeffroy ($1) lists a number of rubidium and caesium salts whose low solubilities make them useful for fractional crystallization; they are not, however, quantitatively insoluble, and most of them exhibit some specificity toward caesium. Of these the best known is the double caesium and antimony chloride (20); the somewhat more insoluble caesium antimony iron chloride (60) is a later modification of Godeffroy’s work. The antimony chlorides are more used at present as specific reagents for caesium than any other, but are not quantitative (39) except under conditions that cause appreciable co-precipitation of rubidium. Murmann (42) reports some very insoluble complex ferrocyanides of caesium, rubidium, and potassium with calcium and magnesium; they are of doubtful composition, they require an excess of alkali to effect precipitation, and their complexity makes them difficult to work with after they have been obtained. Potassium and rubidium picrates, bitartrates, and especially their chloronitrotoluenemetasulfonates ( I S ) are useful for a qualitative separation of these elements from caesium. The last of the three forms the most insoluble compounds, but in the authors’ hands no precipitate could be obtained from solutions containing as much as 10 mg. of rubidium chloride per cubic centimeter; it was found that potassium was more sensitive to the reagent than rubidium, although Noyes and Bray (43) state that 0.5 mg. of rubidium gives an almost immediate precipitate with this reagent. In the hope that there might be some deviation from the rule of increasing solubility with increasing atomic weight, the bromo derivative of this reagent was prepared and tried; it was still less sensitive, however, toward potassium and rubidium than the chloro compound. The literature contains numerous references to microscopic tests (3,17,26,%,64) for the alkalies; these tests usually require rather high concentrations of the elements in question, and claim little or no chemical specificity for potassium, rubidium, or caesium, and consequently have no use in quantitative analysis. Visual spectroscopic (23, 94) methods of estimation have not yet been sufficiently developed to warrant their use in accurate work; spectrographic methods are at present still less serviceable because of the effects of ‘LpuIsion.”l The lower limit of spectrographic sensitivity for salts of potassium, rubidium, and caesium is reached when these salts are reduced to 1 per cent of the diluting medium; using the arc-flame method, the limit is in the neighborhood of 0.1 per cent of the diluting medium.2 When, however, potassium, rubidium, or caesium is present in a silicate rock, presumably as a refractory aluminosilicate, each is very much more sensitive still. Having noticed that reagents for alkalies were used also as precipitants for aIkaloids, the writers tried on the alkalies the effect of a number of compounds that are usually used in alkaloid analysis. Picrolonic acid, xylic acid, o-toluic acid, phenylacetic acid, and phenylpropionic acid gave no precipitates with potassium, rubidium, or caesium. Neither was there any precipitation with phosphoantimonic acid (63). It is known that the potassium ( S 4 ) , rubidium (14), and caesium salts of 12-phosphomolybdic acid are quantitatively insoluble; so also are the potassium ( B I ) , rubidium (16, 18), and caesium salts of 10-phosphomolybdic acid.
EDITION
Vol. 6, No. 2
mention in the literature of its effect on rubidium and caesium, the writers investigated and found that this reagent precipitated both rubidium and caesium quantitatively in the presence of potassium. These unrecorded reactions were then made the basis of a method for the quantitative separation and determination of potassium, rubidium, and caesium. Kehrmann and Bohm (34) prepared 9-phosphomolybdic acid by adding a slight excess of phosphoric acid to the dodeca acid and allowing it to stand for several months; on standing, the dodeca acid gradually lost its power to precipitate potassium, and changed into the luteo acid. Decaphosphomolybdic acid behaves in the same way in the presence of phosphoric acid. Kehrmann and Bohm (34)state that the potassium salt of 9phosphomolybdic acid is about of the same order of solubility as potassium sulfate, and can easily be salted out; consequently too concentrated a solution of potassium salt must not be used in testing for the completion of the reaction. Once precipitated, potassium 9-phosphomolybdate is dissolved again with difficulty. It has been found best, however, to prepare the luteo acid by heating the commercial dodeca acid carefully to between 300” and 350” C. with continuous stirring so as to avoid local overheating; a t this temperature the dry acid turns from orange to green. The temperature is maintained until no orange particles remain; the acid is then cooled and extracted with water. The green solution is oxidized with a little bromine water, and on slow evaporation the short, stout, yellow prisms of the luteo acid separate out. This procedure eliminates an excess of free phosphoric acid in the reagent, the presence of which tends to retard precipitation (68) of the alkali phosphomolybdates. Ephraim and Herschfinkel (18) report a rubidium salt of 9-phosphomolybdic acid, RbsP04.9Mo03, which does not correspond in composition with the potassium salt KaP04.9M003.7Hz0 obtained by Kehrmann and Bohm (34). Several attempts made by the writers to determine the formula of the caesium salt showed that it approximated more closely the composition of the potassium salt, but the analyses were not satisfactory; duplicate analyses of a salt prepared by precipitating caesium with an excess of luteo acid, while consistent in themselves, did not agree with the results obtained when the salt was precipitated in the presence of an excess of caesium, In both cases the summation was low if the molybdenum was calculated to MOOS, and high if calculated to MozOr. For these reasons, no attempt has been made to analyze the rubidium salt. The results obtained with the caesium salt are listed in Table I ; the molybdenum was precipitated as sulfide from a sodium sulfide solution, was reprecipitated as lead molybdate, weighed; and calculated to the oxide; caesium was precipitated from the filtrate as chloroplatinate; the excess chloroplatinic acid was then reduced with zinc, and the phosphorus was separated and weighed as zinc p p o phosphate. I n the salt precipitated in the presence of excess luteo acid, the ratio of the components is as follows: P : Mo = 1 :9.1; P : Cs = 1 : 1.7; and P :HzO = 1 : 6.4 The ratios in the salt precipitated in the presence of excess caesium ion are:
NEW REACTION O F RUBIDIUhl AND CAESIUM
P : M o = 1 : 8 . 8 ; P:Cs=1:2.19; andP:HnO=1:5.4
As luteophosphomolybdic (9-phosphomolybdic) acid (34) mas known to precipitate a number of alkaloids quantitatively, without precipitating potassium, and as there was no
The precipitates are so finely divided that their optical properties give no indication whatever as to whether the material is homogeneous or a mixture. I n order to determine the quantitativity of 9-phosphomolybdic acid as a precipitant for rubidium and caesium, a number of determinations were made on mixtures of known solutions of these salts, each of which had previously been
1 The term “pulsion” has been coined t o designate the variation in intensity of spectral linea a8 conditioned by ionization phenomena (56,44) Work on this subject will be published shortly. * An article on the aro-flame method will be published in the near future.
INDUSTRIAL AND ENGINEERING CHEMISTRY
March 15, 1934
109
verted (22) to chloroplatinate for weighing. Tables I V and V show the quantities of rubidium and caesium recovered separately from their silicotungstates, and Table VI shows the results of the silicotungstic acid separation of rubidium from caesium. The amount of rubidium that can be separated from caesium is governed by the solubility of the former as silicotungSALTOF 9-PHOSPHOMOLYBDIC TABLE I. ANALYSISOF CAESIUM state; the writers have found it advisable to use not more ACID than 0.08 gram of rubidium chloride in a volume of 50 cc. Moos CS POI HzO of 6 N hydrochloric acid, and to use an excess of not more than Gram 'Gram Gram Gram 0.2 or 0.3 gram of solid silicotungstic acid over the amount Salt precipitated in presence of excess luteo acid. Found in required to effect precipitation of the caesium; otherwise the 0.3673 0,0632 0.0263 0.0320 0.5000-gram sample Salt precipitated in presence of exseparation may not be satisfactory. The amounts of potascess caesium ion. Found in 0.3518 0,0804 0.0262 0.0271 sium, rubidium, and caesium used in the preliminary experi0.6000-gram sample Theoretical for CssPO~.9MoOs.7Hz00.3383 0,1040 0.0248 0.0328 ments were chosen primarily from consideration of the actual 0.3621 0.1113 0.0265 Theoretical for CssPO~.9MoOs quantities that will confront the analyst in silicate mineral work. At these concentrations, the caesium recovered is TABLE11. SEPARATION OF RUBIDIUM FROM POTASSIUM BY PHOSPHOMOLYBDIC AND CHLOROPLATINIC ACIDS spectroscopically free from potassium, but usually contains a TAKEN OBTAINED trace of rubidium; on the other hand, the rubidium is enRbCl RECOVERY RbrPtCle RbCl KNOs tirely free from caesium; if potassium was present in the Gram Gram Gram Gram % original mixture, spectroscopic examination may show that a 0.0798 0.0335 98.8 0.0339 1.00 0.0341 100,6 0.0339 0,0812 1.00 small quantity of the potassium has been carried down with 0.0225 99.5 0.0226 0.0540 1.00 the rubidium chloroplatinate. TABLE111. SEPARATION OF CAESIUMFROM POTASSIUM BY TABLE Iv. RECOVERY OF RUBIDIUM FROM SILICOTUNGSTIC 9-PHOSPHOMOLYBDIC AND CHLOROPLATINIC ACIDS ACID BY CHLOROPLATINIC ACID TAKEN OBTAINED
analyzed separately by the chloroplatinate method. For the reasons given above, the precipitates were not weighed directly as such; the molybdenum was first removed with hydrogen sulfide, and the alkali was recovered from the filtrate and weighed as chloroplatinate. The results of these determinations are listed in Tables I1 and 111.
KNOs Gram 1 00 1 00 1.00
CSCl Gram. 0 0205 0 0192 0 0095
CszPtCh Gram 0 0406 0 0380 0 0192
CsCl Gram 0 0203 0 0190 0 0096
% 99 0 98 9 101 0
The final precipitates were examined spectroscopically by the arc-flame method to determine what was being weighed, and in most cases a small amount of potassium was detected. A number of the experiments were repeated, adding the reagent first to potassium alone; when no precipitation had occurred after a long interval, either rubidium or caesium was added, causing immediate precipitation. The continued presence, however, of lines due to potassium in the spectrograms suggests that the potassium was probably adsorbed by the rubidium and caesium phosphomolybdates. Spectrographic examination of the filtrates from the phosphomolybdic acid treatment showed that the rubidium and caesium had been removed. SEPARATION OF CAESIUhl FROM
RUBIDIUM
Having quantitatively removed potassium, the next step was to separate rubidium and caesium from each other. The reagent used for this purpose was silicotungstic acid. Freundler and M h a g e r (19) found that rubidium silicotungstate is soluble to such an extent that 0.4 gram of rubidium per 100 cc. of solution is not recoverable. The writers found that caesium silicotungstate is quantitatively precipitated, in the presence of rubidium, in 6 N hydrochloric acid, and that the rubidium is quantitatively recoverable from the filtrate as chloroplatinate. The precipitation of caesium is much more rapid in 8 N sulfuric acid, but the separation from rubidium is not as sharp as when hydrochloric is used; nitric acid tends to prevent precipitation of both rubidium and caesium silicotungstate. The caesium precipitate is somewhat hygroscopic, and there is a tendency for silicotungstate precipitates to form several hydrates (69), so the caesium was also conTABLEVII. I
KNOs Gram 1.00 1.00 0.80
,
TAKEN RbCl Gram 0.0226 0,0188 0,0226 0,0342
RECOVERY
OBTAINED RbnPtClfi RbCl Gram Gram 0.0532 0.0222 0.0450 0.0187 0.0539 0.0225 0.0812 0.0341
RECOVERY
% 98.2 99.4 99.5 99.7
TABLEV. SEPARATION O F CAESIUM FROM POTASSIEd SILICOTUKGSTIC AND CHLOROPLATINIC ACIDS TAKEN KNOs CsCl Gram Gram 0.20 0.0175 0.20 0.0175 0.20 0.0102 1.00 0.0095
OBTAINED CszPtClo CECl Gram Gram 0.0350 0.0175 0.0350 0.0176 0,0198 0,0099 0.0190 0.0095
BY
RECOVERY
% 100.0 100.0 97.0 100.0
TABLE VI. SEPARATION OF CAESIUM FROM RUBIDIUM BY SILICOTUNGSTIC AND CHLOROPLATINIC ACIDS l
M T A K E~N RbCl Gram 0.0226 0.0342 0.0226
--
~ ~OBTAINED~ CsCl RbnPtCla RbCl CsePtCle Gram Gram Gram Gram 0.0532 0,0222 0.0193 0.0095 0.0816 0.0341 0.0196 0.0095 0.0540 0.0225 0.0370 0,0189
~ CsCT Gram 0.0095 0.0096 0.0185
~ RECOVERY RbCl
CsCl
%
%
98.2 99.7 99.5
100.0 101.0 97.9
The filtrate from the 9-phosphomolybdic acid precipitation contains all the potassium, except as noted above, which can be determined by any of the three standard methods mentioned above. Table VI1 shows the recoveries of rubidium and caesium from known mixtures containing aluminum, potassium, rubidium, and caesium nitrates, by means of 9-phosphomolybdic and silicotungstic acids.
MODIFICATIOXS OB CHLOROPLATIKATE METHOD During long use of the chloroplatinate method the writers have developed several minor modifications thereof that secure more concordant results and greater flexibility of application, without necessity for the usual meticulous precautions.
RUBIDIUM AND CAESIUM FROM POTAE3SIUhl AND FROM EACHOTHER BY 9-PHOSPHOMOLYBDIC, SILICOTUNGSTIC, AND CHLOROPLATINIC ACIDS, IN PRESENCE OF ALUMINUM NITRATE
SEPARATION O F
MIXTVRET A K E N Al(N0s)s RbCl Gram Gram 0.0339 0.50 1.00 0 0226 1.00 0,0226
CsCl Gram 0.0195 0,0095 0.0095
c
RbePtCla Gram 0 0818 0,0540 0,0536
OBTAINED RbCl Cs2PtCla Gram Gram 0.0342 0.0402 0.0185 0.0225 0.0224 0.0196
CRCl Gram. 0.0201 0.0093 0.0098
--RECOVERY-RbCl CsCl
%
%
100.8 99.5 99.1
103.0 98.0 103.1
110
ANALYTICAL EDITION
1. The nitrates of the elements are much more soluble inethyl alcohol than the chlorides. Standard texts on analytical chemistry premise that alkali chlorides must be used in the chloroplatinate method, and consequently the alkalies must first be assembled and removed from all other salts before proceeding with the analysis. It has been found, however, that potassium, rubidium, and caesium chloroplatinates can be precipitated quantitatively without contamination, in alcohol, in the presence of large amounts of sodium, iron, aluminum, manganese, and other salts, provided everything in the solution has previously been converted to nitrate. 2. It has been found more satisfactory to precipitate the alkali chloroplatinates instead of converting to chloroplatinate by evaporation everything that is resent and leaching out the soluble salts. Preci itation is effectei quantitatively and immediately by adding cl%oroplatinic acid to the solution containing 60 to 70 per cent of alcohol by volume, and then adding 2 or 3 cc. of ethyl ether. Direct precipitation of the alkalies has the obvious advantages of rapidity and of eliminating the possibility of positive or negative error through occlusion or decrepitation; furthermore, direct precipitation obviates such objectionable contaminants of the reagent as nitroso- and hydroxychloroplatinic acids (89).
Rubidium and caesium are listed as chlorides in the tables in this paper only for convenience in comparing amounts of standard solutions taken with amounts recovered as double platinum chloride; as will be seen, the chlorides were actually converted to nitrates in all the analyses.
Vol. 6 , No. 2
The excess hydrazine must now be removed from the alkalies, because it forms very insoluble compounds with both silicotungstic and chloroplatinic acids. It is most conveniently removed by boiling for a short time with a little aqua regia, which should be added cautiously; otherwise the reaction may be violent. The solution is now evaporated t o small volume with some concentrated hydrochloric acid to insure complete removal of nitric acid, it is taken up in 50 to 75 cc. of 6 N hydrochloric acid, and to the cold solution is added 0.5 to 1.0 gram of solid silicotungstic acid dissolved in a few cubic centimeters of water. (The reagent supplied by Eimer and Amend has been found very satisfactory.) Precipitation will be incomplete if nitric acid has not been entirely removed. After standing for 12 hours, the preci i tated caesium salt is filtered through a Munroe crucible, ancfi, washed with 6 N hydrochloric acid. The filtrate contains all the rubidium, which is determined as chloroplatinate by evaporating to 10 cc. in the presence of nitric acid and a little chloroplatinic acid, adding 3 times its volume of alcohol together with a small excess of chloroplatinic acid and a little ether, filtering, washing with alcohol, drying, and weighing in the usual way. The excess silicotungstic acid does not interfere with the determination! provided there is a little chloroplatinic present to prevent precipitation of the rubidium as silicotungstate during the process of evaporation.
It is preferable, as has been already stated, t o weigh the caesium as chloroplatinate. T o do this, the silicotungstate radical must be removed, and best results are obtained by the following procedure ($2):
The caesium precipitate is dissolved by the least excess of IMPROYED ANALYTICAL METHOD FOR POTASSIUM, RUBIDIUM, sodium hydroxide; this solution is made faintly acid with nitric
AND CAESIUM The following method is therefore proposed for determining rubidium and caesium in the presence of potassium:
A sample is taken that contains not more than 0.08 gram of rubidium chloride and not more than about 1.0 gram of potassium chloride. The sample is dissolved in 100 cc. of nitric acid (1 to 3), heated almost to boiling, and treated with 9-phosphomolybdic acid until precipitation is complete, observing the usual recautions of the similar standard method for the precipition ofPammonium phosphomolybdate. When the yellow precipitate of rubidium and caesium 9-phosphomolybdate has settled, it is filtered through a Munroe (.41,67) crucible, and washed with 1 er cent sodium nitrate solution. The filtrate now contains alfthe potassium, which can be determined by any of the first three methods mentioned. The phosphomolybdate precipitate is then dissolved in the least necessary amount of dilute sodium hydroxide solution; the resulting solution is saturated with hydrogen sulfide, heated to boiling, and made just acid with nitric acid; this usually serves to precipitate all the molybdenum as sulfide. The solution is then boiled to coagulate the precipitate, which is filtered off, washed, and discarded. It is essential that the molybdenum be removed from the rubidium and caesium, otherwise their very insoluble phosphomolybdates will reprecipitate and interfere with the separation of one from the other; the sulfide method has been found to be the most satisfactory for this purpose. If some molybdenum is reduced and left unprecipitated, it can readil be oxidized by boiling with a little bromine water, and after cool ing can be treated again with hydrogen sulfide. Caesium can be separated from rubidium in the filtrate by the silicotungstic acid method described below, but because of the phosphates present it has been found more satisfactory first to concentrate these alkalies as chloroplatinates. The filtrate from the removal of molybdenum is evaporated to about 20 cc., and after adding 60 cc. of 95 per cent alcohol, is treated with a slight excess of chloropbtinic acid, and then a few cubic centimeters of ether are added; after the precipitate has settled it is filtered through a Munroe crucible. Besides rubidium and caesium, the precipitate always contains a little sodium phosphate; consequently it cannot be weighed a t this stage. After washing with 80 per cent alcohol, a fresh receiver is placed under the crucible, and to the latter are added a little distilled water and 2 or 3 drops of hydrazine hydrate; the reaction is then allowed to proceed till vigorous evolution of gas ceases. Complete reduction of the chloroplatinates takes place immediately, with the formation of platinum and of the chlorides of the alkalies. Suction is then applied, and the alkali chlorides are washed into the flask.
acid, is diluted to 200 cc., and to it in the cold is added 10 per cent mercurous nitrate solution till precipitation is complete’ a t this point, the mercurous silicotungstate flocculates and settles rapidly, The precipitate is filtered off, washed with 1 per cent mercuroua nitrate solution, and discarded. If an electrolyte is not present in the wash water, the mercurous silicotungstate will be peptized and will pass through the filter aper. Then the excess mercurous salt in the filtrate is oxidizefwith a little aqua regia to the mercuric state, when it is uite soluble in alcohol; the solution is evaporated to 10 CC. aslor the determination of rubidium, treated with three times this volume of alcohol, then with chloroplatinic acid and with ether, and the caesium is filtered off and weighed as chloroplatinate.
The method proposed does not afford the clean-cut sharpness of separation that is desirable in an accurate quantitative procedure; on the other hand, it compares favorably with a number of other standard methods in current use for the determination of elements that are chemically not so closely allied as are the rare alkalies, such as silicop, germanium, tin, and arsenic; this method is furthermore much more reliable than those hitherto proposed. The average error introduced in the course of analysis by this method is 1 2 per cent, which could conceivably be reduced by the use of larger amounts of material. No effort hqs been made t o use larger amounts because, on account of the rarity of rubidium and caesium, the quantities dealt with in this paper represent what the analyst will ordinarily encounter. The method is now being applied in the analysis of some rubidium- and caesium-bearing minerals. LITERATURE CITED (1) Auger and Karantassis, Compt. rend., 180, 1845 (1925). (2) Ball, J . Chent. SOC.,95,2126 (1909). (3) Bayer, Monatsh., 41, 223 (1920). (4) Brauner, Collection Czechoslov. Chem. Communicatims, 2, 442 (1930). ( 5 ) Browning and Spencer, Am. J. Sci., [41 42, 279 (1916). (6) Brukl, Monatsh., 56,179 (1930). (7) Bunsen, R.,Ann., 119,107 (1861). (8) Ibid., 122,347 (1862). (9) Burkser, Milgewskaja, and Feldman, 2. anal. Chem., 80, 264 (1930). (10) Carnot, Be?., 9,1434 (1876). (11) Chamot and Mason “Handbook of Chemical Microscopy,” Vol. 2, p. 84,Wiley, 1931. (12) Clarke, Am. J. Sci., [3]32,356 (1886). (13) Davies and Davies, J . Chern. Soc., 123,2976 (1923).
March 15, 1934 (14) (15) (16) (17) (18) (19) (20) (21) (22) (23) (24) (26) (26) (27) (28)
(29) (30) (31) (32) (33) (34) (35) (36) (37) (38) (39) (40) (41) (42) (43)
INDUSTRIAL AND ENGINEERING CHEMISTRY
Debray, Bull. soc. chim., 5, 404 (1866). Debray, Compt. rend., 66, 704 (1868). Drechsel, Ber., 20, 1453 (1887). Emioh, Monatsh., 39, 775 (1918); 41, 243 (1920); 46, 261 (1925). Ephraim and Herschfinkel, 2. anorg. allgem. Chem., 65, 237 (1910). Freundler and MBnager, Compt. rend., 182, 1158 (1926). Godeffroy, Ber., 7, 375 (1874). Ibid., 8, 9 (1875). Ibid., 9, 1363 (1876). Gooch and Hart, Am. J. Sci., 131 42, 448 (1891). Gooch and Phinney, Ibid., [3] 44, 392 (1892). Gravestein, Mikrochem., Emich Festschr., 2, 135 (1930). Heller, Haurowitz, and Starry, Ibid., 2, 182 (1930). Hess and Fahey, A m . Mineral., 17, 173 (1932). Hillebrand and Lundell, “Applied Inorganio Analysis,” p. 529, Wiley, 1929. Hillebrand and Lundell, Ibid., p. 39. Huysse, 2. anal. Chem., 3 9 , 9 (1900). Jander and Busch, 2. anorg. allgem. Chem., 187, 165 (1930); 194, 38 (1930). Jander and Faber, Ibid., 179, 321 (1929). Jenzsch, Ann. Physik, 180, 102 (1858). Kehrmann and Bohm, 2. anorg. allgem. Chem., 7, 406, 425 (1894). King, A. S., Astrophys. J., 55, 380 (1922). Klein, Bull. soc. chim., [2] 36, 17 (1881). Marignao, Ann. chim. phys., [4] 3, 5 (1864). Moser and Ritschel, Monatsh., 46, 9 (1925). Moser and Ritsohel, 2. anal. Chem., 70, 184 (1927). Muller, Proc. Am. Phil. Soc., 65, Suppl. 5, 44 (1926). Munroe, J. Analytical and Applied Chem., 2, 241 (1888); Chem. News. 58. 101 (1888). Murmann, E.; Oesterr. ’ChevkZtg., 28, 42 (1925); Chem. Ah., 19, 1827 (1925). Noyes and Bray, “A System of Qualitative Analysis for the Rare Elements,” p. 266, Macmillan, 1927.
111
(44) Papish, J., and O’Leary, W. J., IND. ENG.CHEM.,Anal. Ed., 3, 11 (1931). (45) Parmentier, Compt. rend., 92, 1234 (1881); 94, 213 (1882). (46) PBchard, Ibid., 110, 754 (1890); Ann. chim. phvs., [6] 22, 187 (1891). (47) Pennington, J. Am. Chem. Soc., 18, 56 (1896). (48) Preis, J. prakt. Chem., 103, 410 (1868). (49) Rayman and Preis, Ann., 223, 326 (1884). (50) Reed and Withrow, J. Am. Chem. Soc., 51, 1062 (1929). (51) Robinson, W. O., J. IND. ENQ.CHEIM., 10, 50 (1918). (52) Scheele, Svenska Vet. Akad. Hand., 33, 120 (1771); Mellor, W. J., “Comprehensive Treatise on Inorganic and Theoretical Chemistry,” Vol. 6, p. 947, Longmans, 1925. (53) Schulse, Ann., 109, 177 (1859). (54) Schwarz and Giese, Ber., 63, 2428 (1930). (55) Sharples, Am. J. Sci., [2] 47, 178 (1869). (56) Smith, G. F., and Shead, A. C., J. Am. Chem. Soc., 53, 947 (1931). (57) Snelling, Ibid., 31, 456 (1909). (58) Sonnensohein, J. prakt. Chem., 53, 339 (1851). (59) Stolba, Dinglers polytech. J., 198, 225 (1870). (60) Strecker and Dias, 2. anal. Chem., 67, 321 (1925). (61) Svanberg and Struve, J. prakt. Chem., 44, 291 (1848). (62) Tananaeff. 2. anal. Chem.. 88.343 (1932). (63j Tananaeff’and Harmasch, Idid., 89, 256 (1932). (64) Vogel, Monatsh., 46, 265 (1925). (65) Wells, Am. J. Sci., [3] 45, 121 (1893); [3] 46, 186 (1893); 2. anora. allgem. Chem., 45, 121 (1893). (66) Wells a n d Fooie, Am. J. Sci., [413, 461‘(1897). (67) Wernadski, Bull. soc. franc. mindral., 36, 258 (1913). (68) Winokler, J. prakt. Chem., 121, 36, 177 (1887). (69) Wyrouboff, Bull. soc. franc. minbral., 19, 219 (1896). (70) Yajnik and Tandon, J.Indian Chem. Soc., 7,287 (1930); Chem. Ahs., 24,4236 (1930).
RECEIVED August 29,1933. Extract from a theeis submitted to the faculty of the Graduate Sohool of Cornell University b y Wm. J. O’Leary in partial fulfilment of the requirements for the degree of Dootor of Philosophy.
Retention of Dichromate by Glassware After Exposure to Potassium Dichromate Cleaning Solution EDWINP. LAUG,Chemical Room, Marine Biological Laboratory, Woods Hole, Mass.
I
T HAS perhaps not been generally realized that the use of cleaning solution (HzS04.KzCr207 mixtures) may be a source of trouble in biology, chiefly through contamination of media kept in contact with glassware cleaned by this method. Some workers, suspicious of cleaning solution, have regarded the ordinary rinsing with tap water and distilled water as inadequate] and have resorted to longer periods of washing, the assumption apparently being, that whereas rinsing removed the cleaning solution on the surface of the glass, it did not extract that which had penetrated into the glass. As far as can be gathered from the literature, no systematic biological or chemical assay has ever been attempted to determine the adequacy of rinsing and washing procedures in ridding glassware of cleaning solution. a,6-Diphenylcarbohydrazide (C6HsNHNH)2C0 has been known for a long time. I n 1900 Cazeneuve (2) suggested i t as an extremely sensitive reagent for detecting potassium chromate. It was subsequently used by Barnebey and Wilson (1) as an indicator for the dichromate titration of iron. Chromate or dichromate oxidizes a, d-diphenylcarbohydrazide to diphenylcarbazone (NH2NHCON:NH), a reaction which gives a well-defined pink coloration to the solution and is so delicate that 0.0001 mg. ( 0 . 1 ~ )can be easily detected. Moreover, in somewhat greater concentration, the color value is adaptable for a colorimetric determination.
PROCEDURE ,+Diphenylcarbohydrmide was prepared by dissolving 0.5 gram of the dry powder in 70 ml. o 95 per cent alcohol and 25 ml. of glacial acetic acid and making the solution up to 100 ml. with distilled water in a volumetric flask. The reagent keeps about 3 hours at room temperature, after which a pink color develops, presumably due to an oxidation similar t o that effected by the chromate. The standards were prepared so as t o contain respective1 5.0, 4.0, 3.0, 2.0, 1.0, 0.57 of potassium dichromate per 5 m l To each of these tubes 1 ml. of the oc,&diphenylcarbohydrazide reagent was added. It required about 10 minutes at room temperature for the full pink color t o develop. After about 45 minutes the color gradually began to fade, so that it was necessary to make all comparisons at least within 0.5 hour after the standards and unknowns had been prepared. For the comparison a Klett colorimeter was used with 5-ml. cum. Concentrations below 0.57 were not adaptable for measurement in the colorimeter because of low color value, but were simply roughly estimated. In general, anything less than 0.27 was considered a trace.
It was assumed that ten rinsings with water, seven of tap and three of distilled] constituted adequate removal of all potassium dichromate from the surface of the glass. This was borne out by tests. However, any potassium dichromate which hard in some manner been retained within the glass might not be so quickly removed by rinsing. Hence all the tests reported were done on wash waters which had been in contact with the glass for various lengths of time. These extractions with water were sometimes repeated twice in
