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A study of platinum glyoxime as a suitable substance for the estimation of the atomic weight of the metal Phillips, George Lindsay 1938

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J. SSD3Y OF PLATIEUIc SLYOXILS A3 A SUITABLE SUB82A1ICE FOE. THE ESlIIvMSICU OF TEE ATOiHC \73IGEE OF THE 122EAL George Lindsay Phi l l ips i Thesis submitted for the Degree of MASTSB OF ARTS in the Department of CHEM1STHY i. Study of Platinum GlyoziEc- as a Suitable Substance for the Estimation of the Atonic Weight of the l letal ." Table of Contents, I . Introduction. II . Bevie-7 of Earl ier Determinations. III. Comparison of Mass Spectrum Measurements with the Chemical Atomic Weight, Page. 7. IV. Purif ication of Reagents. V. Calibration of Apparatus. VI. Preliminary Investigation with Nickel Glyo~ime. 8. VII. Ohloroplatinic Acid, 12. VIII. Ohloroplatinic Acid with Dimethylglyoxirae. 1 5 . IX. C-hloroplatinous Acid with Dlmethylglyoxime. 20. X. Chlorides and Oxides of Platinum. 25. XI. Summary. XII. Aclaiowl edgment. XIII. Bibliography. 27. 27. figures Facing page 1. Hydrogen treatment of Fickei £lyoxime. 9. 2, Chlorine treatment of ITickel C-lya>:ime. 10. 5. Oxygen treatment of Mcfcel Glyoxime. 10. 4. Reduction of Potassium Chloroplatinate. II . 5. Electrolysis Apparatus. IS. 6. Y/eber's Electrolytic Ce l l . 13'. 7. E lectr ic heater., 15. 8. Treatment of .brovm precipitate in Carbon Dioxide. 16. 9. Treatment of bro\m precipitate in GOo at reduced pressure.17. 10. Kitrogen treatment of brov/n material. 17. 11. Chlorine treatment of brov.n material, 18. 12. Treatment of Platinous Diiaethylglyosime. 23. "'A Study of Platinum Slyoxime as a Suitable Substance for the Estimation of the Atomic Weight of the Metal". Introduction. The atomic weight of platinum was studied by Dr. 3.H. Archibald(I some thirty years ago by an analysis of potassium and ammonium chloroplatinates and "bromoplatinates. The value obtained in this determination is the atomic weight accepted by the International Committee (1937). However, as this value is based entirely on the atomic weights of chlorine, s i lver , potassium and bromine, i t was thought that i t would be of considerable interest i f another set of ratios could be established with constants quite independent of those previously used. Farther, a great many improvements in the techniquer.that has to do with atomic weight determinations have been introduced and by following these modifications a more exact value for the constant in question might be obtained. Since organic compounds are used successfully in determining the atomic weights of metals, i t was thought, i f a suitable reagent could be obtained, that platinum might be precipitated in combination with this substance in a form that could be weighed with accuracy and precision and whereof the platinum content could be exactly estimated. The high degree of purity and the reduced cost of organic reagents lend support to this proposal. Dimethylglyoxime Is one instance of an organic compound that (1) Archibald, E.H., Proc. Roy. Soc. Edinburgh XXIX., 721-747, (1909 ). has proven to "be particularly useful in analytical work. It is used in nickel determinations and in quantitative estimations of palladium. Addition of dimethylglyoxime to an ammoniacal solution of a salt of nickel gives a br i l l i ant red precipitate of an acid salt . M(OH) + 2 [H01T)C ( C H _ ) — > 2H_0 + KIEL {0_JT 0 (CH.) J . 2 2 2 3 2 2 < 2 2 2" 5 2 2 . The precipitate is insoluble in water(2) and is very sl ightly soluble in alcohol and glacial acetic acid. The compound wi l l sublime at 2 5 0 G . and SIIGWS marked stabi l i ty at this temperature { 3 ) . By using an organic reagent, such as dimethylglyoxime, i t should be possible to prepare the platlnous salt as well as the plat in ic sa l t . Previous investigations were chiefly a study of plat inic ' sa l ts . The formation of an insoluble and stable compound would make the determinations comparatively simple assuming that the compound can be pur i f ied. Many experimental errors incident to the usual atomic weight estimations would thus be eliminated. ( 2 ) Brunck, 0., Z. Angew Chem. 2 0 , 3 8 4 4 ( 1 9 0 7 ) , Ghem. Ab. 2 : 2 4 0 ( 1 9 0 8 ) . ( 3 J Brunck, 0 . , ibid 2 0 , 8 3 4 ( 1 9 0 7 ) , Ghem, Ab. 2 . -46 ( 1 9 0 8 ) . (3) T^r-.vi p^-n of Ray Tier detarmjTiat-S ons. The study of the atomic weight of platinum is recorded in the works of J . J . Berzelius{4), T. Andrews, K. Seubert, V;. Halbersta w. Dittmar, J . LIcArthur and E.H, Archibald and covers a period of re-investigations dating from 1826 to 1909. Berzelius and Andrews obtained values that were more than one percent above these of later investigators. J .S. Stas pointed out the d i f f i cu l ty involved in removing the last traces of water from potassium chloroplatinate and suggested this as a possible source of error. Berzelius analyzed the double salt of potassium chloride and p lat in ic chloride and found ratios between the salt and its constituents. Andrews also worked with potassium chloroplatinate, decomposing the salt by means of zinc and water. K9 Seubert decomposed ammonium chloroplatinate and potassium chloroplatinate in a stream of hydrogen and determined the several ratios between the salts and si lver chloride. Seubert's results were confirmed by W. Halberstadt, who studied the ammonium and potassium salts of bromoplatinic and of chloroplatinic acids. Seubert's and Halberstadt's values were 195.22 and 195.05 respectively. Analyses of potassium chloroplatinate by V/. Dittmar and J . IIcArthur involved corrections for hydrolysis. They held that the salt was seldom pure because of the tendency for chlorine to be replaced by hydroxyl and for potassium to be replaced by hydrogen. The results which they obtained give a value of 195.5. E. H. Archibald obtained ratios from the analyses of (4) l iel lor, Comp. Treatise on Inorg. and Theoretical Chern. Yol XVI. potassium and ammonium chloroplatinates and bromoplatinates and .compared platinum and its salts with silver and its halides. Conversion of the metal into the salts of brompplatinic and ohloroplatinic acid by electrolysis removed any source of contamination from nitric acid. Precaution was taken against hydrolysis by heating to expel any absorbed and occluded moisture. The best representative value from E.H. Archibald's determination is 195.23. Comparison of Mass Spectrum Measurements with the Chemical Atomic Weight. It is only recently that values for the atomic weight of platinum have been determined by mass-spectrum analysis. Sampson and Bleakney{5) used a new type of ion source and a mass spectrograph of extremely high resolving power to find the relative frequency of platinum isotopes. The following measurements were"obtained in their analysis: "Mass number 192 194 195 196 198 Percentage abundance 0,8 30.2 35.3 26.6 7.2 By assuming a packing fraction from Aston's curve(6) of 0.5, they obtained a value which is identical with the accepted atomic weight. (7) 0. Hahn obtained 195.II ± 0.5 by using the same percentage frequency, but a different conversion factor,of 1.000275, in place of the Me'rcke and Child's factor (1.00022). The argument in favor of a change in the conversion factor is that the values based on measure-ments of isotopic masses will be, for most of the elements, in closer agreement with the chemically determined constants. (5) Sampson and Bleakney, Phy. Bev.,L.8, 734 (1936) (6) Aston P.W. Mass Spectra and Isotopes (1933; (7) Hahn 0 . , Bar. 71.I (1938) Purification of He^ssrts. Y/ater; Aedistillsa water vac used throughout the investigation, liooley said Phillips * apparatus(6) was. used in tho second distillation, Alcohol: 357' ethyl alcohol tas put into a 2-IIter flask, lui.ps of quicklime v/src added and the flash shaken every few hours for several days. Some of the alcohol v/ac transferred to a dry flash and distilled. The first and last portions of tho distillate were discarded. Dlmothyl,r:lyo::ime: A preliminary test of tho relative solubility of the coiijpound in cold and hoi alcohol vrets made by treating the substance with 10 c.c. of alcohol. It .was found that 0,163 grams of solute dissolved in 10 c.c> on shaking tho aiixtura for one hour at 2? *0. and that 0,60 grams dissolved at.7C*0. These weights, however, do not express the absolute solubility at these two temperatures, since insufficient time was allowed for complete saturation. Adams and hamm's method of crystallization(9) was used in purifying the compounds 25 grams of dimethylglyoxlme were added to 500 c.c. of distilled alcohol and a hot saturated solution prepared. The solution was filtered by suction through a heatod funnel and tho filtrate obtained wag cooled rapidly with frequent shaking. The crop of white crystals was washed into a porcelain G-ooch crucible, filtered by suction, washed with alcohol and dried for several hours 10] Hooley and Phillips, J. Chem. 2duc. II, 576 (1934). (y) Adams and Kamm, J. Am. chem. S0Q. 40, I26I-9, (i9i 8 (6) at 120°C. The alcoholic f i l t rates were used repeatedly In preparing more crystals. Potassium chlorp-platinate:The salt used In the investigation was purif ied "by Dr. B.H. Archibald fsnom purif ied potassium chloride and ohloroplatinic acid. The potassium chloride was twice precipitated from solution by gaseous hydrogen chloride and washed and dried by centrifuge. The salt was used in the precipitation of potassium chloroplatinate, which In turn was reduced to potassium chloride and the metal. A pure product was obtained by precipitating the potassium chloride twice from solution by hydrogen chloride. Ohloroplatinic acid was made by dissolving spongy platinum in concentrated hydrochloric acid by an electrolytic method. The potassium chloroplatinate was formed by adding dilute ohloroplatinic acid slowly to a dilute solution of pure potassium chloride. The precipitates were thoroughly washed with water and alcohol. The product obtained was reduced in pure hydrogen and the platinum again dissolved and precipitated as before. This operation was repeated four times. The potassium chloroplatinate used by Eoyes and \7eber(l0) was made from electrolyt ical ly prepared ohloroplatinic acid. Hydrochloric acid: Concentrated C P . acid was d is t i l l ed from Pyrex quarter ' the f i r s t and last portions being discarded. (10) Koyes and Weber, U.S. Bureau of Stand., Bulletin, 4, 347, (1907-8j. Sodium Oxalate: Tvo methods of purification were roco:ei.-.enaed "sy Soreiisen(II ] s e .g . , crystallization from v/ater and precipitation from aqueous solution "by alcohol. Alcoholic precipitation has the disadvantage of yielding a product which is more hygroscopic than that crystallized froia water. The Bureau of ntan&ar&s reports that two crystallizations from water are sufficient to effect j>urifi cation. 60 grams of sodium oxalate were added to one liter of water and the mixture was boiled for 10 minutes, ( The solubili is 3 grams at 20°G. and 6 grams per 100 ml. at I00°C.) The hot solution was decanted and cooled to room temperature. The mother liquor was poured off the crystals. 275 o,e, of water were added to the crystal masj, the temperature was raised and th? whole operation repeated, The crystals wers dried at 70*0. Calibration of Apparatus. Oalihration of pipetted; First pipette; average v/eight of water for throe trials is 4.6417 g Temperature Is ie^C. 4.6417 go of water at IC ; /c occupy 4 = 6673 ml. Second pipette: average weight of water for four trials Is 4.9854 g Temperature is IGf/o, 4.0SD4 g. of water at ICUQ. occupy 5 = 0129 nil* . (II) U . S . Bureau of -tana. Circuit F 0 „ ^ S T T? AT- cn -, (8) . Calibration of volumetric flask: Average volume for three t r ia ls is 100.0652 ml. Apparent "/eight Temp. Yolo of i_js.. Yal^£s£^JttcoxsL&sLj8&.» of water 99*. 6981 g. 23°C. 1.0035 ml. 100.0459 ml. 99.6774 g, 26 °C. 1.0042 ml. 100.0960 ml. 99.7247 g. 22°C. 1.0033 ml. 100.0538 ml. Preliminary investigation with nickel glyoxime. A few of the experiments of other investigators having to do .v/ith nickel glyoxime as a form in which to precipitate and weigh nickel are here set forth. 0. Brunck's method of determining nickel by dimethylglyoxime lire c ipi tat ion was found by Oongdon and Beige (12) to give a value for preoipitated nickel agreeing with the theoretical value. Parr and Lindgren's method(13) of treating the nickel salt with dimethylglyoxime in large excess seemed unnecessary and the amount used in this determination was sl ightly less than twice the amount required for complete precipitation. A sample of nickel sulphate weighing 6.6686 grams was dissolved in 505 ml. of water containing 5 ml, of concentrated sulphuric acid. 50 ml. of solution was'drawn off for the determination. She solution was diluted to 120 ml. , heated• nearly to boiling and treated with 100ml. of alcoholic solution of dimethylglyoxime. 2 grams of aamonium acetate were added to buffer the (12) Oongdon and Beige, Ohem. Hews I2G, 67-8 (1924) (13) Parr and Lindgren, Trans.. Am. Brass Pounders' Assn. 5„I20~9 Facing page 9 . Figure I . i 110 V. R K Zinc and hydrochloric acid. Wash "bottle with water. U-tube containing caustic potash. Beaker containing crucible and nicke l compound. E l e c t r i c heater. solution, jbhc-r. ammonium hydroxide was added to completely neutralise the solution, The slightly alkaline solution was heated until precipitation was complete, The precipitate was collected and washed in a weighed platinum C-ooch crucible. Then the precipitate was dried for 7 to 9 hours at I40°C. and weighed. The following results were o obtained in three trials using 0.6602 grams of nickel sulphate in each £0.*. :7t. of K l -S lTOsl ina V/t. of F ickel Szptal 3 Hi Ilrrpr 1. 0.7205 g. 0,1464 g. 22,I7;b o.67fi 2. 0,7170 g . 0.1457 g. 22.0C^  1.07';! Z. 0,7156 g. 0,1454 g. 225.o4y 1.25,1 Possible sources of error include the slight solubility of the precipitate(14} and slight loss of material in the transfer from flask to crucible. Treatment of ITjcksl Dimethylglyoxima. The scarcity of reliable information concerning the properties of the nickel compound led us to examine its behaviour under conditions that were likely to obtain when v/e were dealing with the corresponding platinum salt. To a certain degree tho properties could be expected to be analogous and information regarding the glyoxime- of nickel could bo transferred to the platinum compound. In pedicular we wished to find out how it would behave when heated in certain of the common gases. Hydrogen: The gas was passed over nickel glyoxims for 3fc- hours at o 190 0. i:o appreciable chang: in weight v/as recorded and no change (14) ITuka j?. , Z. Anal. Ghem. 91, 2S-32, (1332) £ — : A/WVW-R 1. Potassium permanganate. 2. Cone, hydrochloric acid. 3. TTiolcel dimethylglyoxime. 4. Sodium hydroxide solution. Figure 3. I. potassium chlorate and manganese dioxide. 2 o Potassium hydroxide. 3. Boat containing "blade residue. 4. Calcium hydroxide. ppearance of the material. Oxygen: Cue C02350uad was heated in an atmosphere of oxygon as follows: 60 minutes at 210*0. without any change in appearance- or in weight. 60 minutes at 270-277*0. without any change in.appearance or in weight. Chlorine: She gas was generated by dropping concentrated hydrochloric acid on potassium permanganate crystals (Figure 2). Chlorine reacted with the nickel compound at 50*0. producing dense white fumes. The temperature was raised to 155 0. without further change. A black residue remained In the crucible. Loss in weight was 0,2502 grams. Oxygen treatment of the black fesidue from the above experiment* Oxygen was passed over the residue heated to several temperatures. ITo carbon dioxide was produced at 212°0. and no change in weight •was recorded after heating at this temperature for one hour. Hydrogen treatment of the black residue; Hydrogen was passed over the black residue for 2 ; i hours at 210 0. without any change talcing place. Oxygen treatment in the ignition tube (Figure 3). The residue in the platinum G-ooch-crucible was transferred to porcelain boats. A stream of oxygen was jessed over the black residue and the temperature was raised slowly. Part of the residue turned gray, then became orange-colored at a higher temperature. Intense heating caused volat i l isat ion of part of the residue leaving a white deposit. The loss in weight was 0.I3I6 grams, Hydrogen treatment in the ignition tube: The orange-colored material turned gray when treated with hydrogen. Continued heating for 50 minutes caused no further change. The loss in weight was 0.0545 grams. Facing page.II. Figure 4. 1 . -Hydrogen generator. 2. Wash bottle. 3 . Potassium hydroxide. 4. Potassium, chloroplatinate (II) Chlorine treatment in tlie ignition tube; Chlorine converted the gray ash to the orange-colored "body. The gain in weight was 0.0371 grams. Hydrogen treatment in the ignition tube: The operation was repeated producing the gray ash, Keating was continued for two hours after the formation of the gray body. The loss In weight was 0,0437 grams. Conclusion regarding nickel dimethylglyoxime, 1. The formula of the compound produced by treating nickel sulphate with dimethylglyoxime is Hi (C^ H^ IT^ O^  ) . 2. The compound is stable, ITo decomposition takes place in oxygen at 277°C. 3. The compound Is insoluble in water and in alcohol. 4. Hickel dimethylglyoxime reacts with chlorine,Oxygen and hydrogen react with the product obtained by the chlorine treatment. 5. The results of the preceding series of experiments suggest a procedure for reducing platinum dimethylglyoxime to the metal. Once the compound is obtained in a pure state i t can be treated with chlorine and the product reduced with hydrogen. Reduction of Potassium Chloroplatinate. Potassium chloroplatinate v/as reduced to spongy platinum by heating the yellow salt in hydrogen. The train, which is represented in Pigure4, includes: I . Hydrogen generator. 2. T/ash bottle. 3. Drying tube. 4. Ignition tube. A l l joints were sealed except for the rubber stoppers in the generator and at the exit from the Figure 5. © Jopper v/ire« Ilercury. Platinum gauze cathode. • '. Gup. Platinum anode, Mercury. (12) ignition tube. The hydrogen was generated by the action of dilute hydrochloric acid (Baker's C P . acid) on sine metal (Baker's C P . granular). The gas was washed in d i s t i l l e d water and dried by caustic potash pel lets . Cautious heating of the salt converted some of the yellow powder to platinum black. Increased heating in a steady stream of hydrogen converted the remainder of the salt to platinum black. Complete reduction was assured by heating the salt in hydrogen for 60 minutes. Most of the platinum black was converted to spongy platinum at the higher temperature. A series of runs were made to get enough spongy platinum for a determination. The reaction takes place as follows; K 2 PtC l 6 + 2H2 —> 2KC1 f Pt f 4HC1. The potassium chloride was separated from the platinum by repeated washing. The treatment was continued unt i l no trace of chloride ion could be detected with si lver nitrate solution. Preparation of Ohloroplatinic Acid. Platinum was brought into solution e lectrolyt ica l ly . Apparatus for the purpose was kindly loaned by Dr. E.H. Archibald. It consisted of a platinum-gauze cathode and a glass cup f i t ted with a platinum anode (Figure 5). Spongy platinum was put into the cup of the ce l l and lowered into the glass tube containing redist i l led hydrochloric acid. The cathode was put into the acid and a current of 0,6 amperes was passed through the solution. The ohloroplatinic acid was formed in the cup as an orange-red solution which diffused slowly through the hydrochloric acid. The accumulation of chlorine at the base of the cup made i t necessary to use a weak current. The deposition of platinum on the (13) cathode was. due to dissociation of some chloroplatinic ions, P t C l " . 6 PtCl Pt + 6G1 6 T/hen nearly a l l the platinum had been dissolved the orange solution was drawn off by a pipette and f i l t e r e d . The volume of the solution was r reduced from 400 c.c. to 100 c.c. by evaporation under reduced pressure. Weber prepared chloroplatinic acid i n an e l e c t r o l y t i c c e l l (15) of s l i g h t l y different construction. His c e l l consisted of a c y l i n d r i c a l tube drawn out into a siphon. A sheet or disk of perforated platinum was f i t t e d into the glass tube (Figure 6) for an anode. A piece of platinum wire was welded to the disk and at the other end the wire was led through a glass tube containing mercury. Kotches at the top of the c y l i n d r i c a l tube supported the cathode chamber which consisted of a porous porcelain f i l t e r . The platinum cathode was suspended from a watch glass which also served as a doverrfor the apparatus. The chloroplatinic acid was siphoned from the c e l l . Beduction of Chloroplatinic Acid by Hydrogen. The following experiment was performed i n order to find the weight of platinum contained i n a given volume of chloroplatinic acid solution. 4.667 ml. of solution were run into two weighed porcelain boats. The solution fwas evaporated slowly to dryness on a hot-plate. Orange-colored crystals remained. The boats were transferred to an igni t i o n tube and hydrogen was passed over the orange crystals, forming a gray product. The weights obtained were as follows: (14) F i r s t solution: Weight of boats I,2. Weight of boats and Pt. Weight of platinum Second solution: Weight of boats 1,2 Weight of boats + Pt. Weight of platinum Weight of counterpoise 4 0.4800 g. Weight of counterpoise 4 0.6005 g. 0.1203 g. weight of counterpoise + 0.3570 g. Weight of counterpoise + 0.5896 g. 0.2326 g. Reduction of Galoroplatinic Acid by Sodium Oxalate. Chloroplatinous acid and ohloroplatinic acid were both used i n the preparation of insoluble platinum s a l t s . The former solution was obtained from ohloroplatinic acid by reduction with sodium oxalate(16). 2.26 grams of rec r y s t a l l i z e d sodium oxalate were dissolved i n 75 c.c. of water at 70°C. The solution, at 60°C, was added to the ohloroplatinic acid solution, which was at the same temperature. The resulting mixture was kept at 60 G. for one hour, then allowed to cool slowly. I t appeared'to be somewhat lig h t e r i n color after standing for 18 hours. The volume of the solution was reduced to 40 c.c, by slow evaporation at 75°C. The equation for the reaction i s : H P t C l t Ha C 0 -* ILPtCl + 21TaCl + 2C0 o. 2 6 2 2 4 ^ 3 2 In a preliminary test on the reduction of ohloroplatinic acid, a cry s t a l of oxalic acid was added to three drops of ohloroplatinic acid solution diluted with an equal volume of water. The solution was kept at 70°C. for 15 minutes without any noticeable change, Then, the (16) Hopkins, Chemistry of the Rarer Elements, page 358. Figure 7. (15) solution was divided into'two equal parts and one part treated with sodium hydroxide. IText, dimethylglyoxime was added to each solution and the temperature kept at 45 *C. for 48 hours, i n insoluble brown material formed in each.solution,with greater precipitation occurring in the alkaline solution. Treatment of Chloroplatinic Acid with Dimethylglyoxime. 65.338 ml. of chloroplatinic acid solution were measured out with a calibrated pipette. The volume of the solution was reduced to 40 c .c . by slow evaporation and the temperature was brought to 40°C. The warm acid was added to 300 c .c . of an alcohol solution,containing 4.5 grams of recrystall ized dimethylglyoxime. The amber-colored solution was cooled to zero°C. and kept at this point for 8 hours. A fine crystall ine material appeared in the solution. Then, the temperature was kept at 35°C. for five days, producing a flocculent brown precipitate. The volume of the mixture was reduced to 175 c .c . by warming at 70C. Thompson, Beamish, and Scott(17],in their study of p lat in ic glyoxime, heated the mixture on a steam bath, whereas in our investigation the temperature was kept constant by using an electric heater (Figure 7). The precipitate was separated by f i l t ra t ion and the residue washed with 20 c.c. of alcohol at 70°C. The lustrous precipitate was digested in 25 c .c . of alcohol for 40 minutes at 64 °C., then ref i l tered. A brown crystall ine mass separated from the f i l t ra te after standing for one week. (17) Thompson, Beamish and Scott, J . of Ind. and Eng. Chem., .Anal. Ed. Sept., 1937. Facing page 16. 1. Calcium carbonate and hydrochlor 2. Calcium chloride, 3. Boat containing brown residue. (16) Treatment of the brown residue.  S o l u b i l i t y . Water: The s o l u b i l i t y of the residue was slight at both zero C. and at 100°G. The f i l t r a t e from the digested material had a blue color and on reducing the volume a blue body separated. With further reduction the blue material became f i n e l y dispersed. A flocculent bluish-black material separated on standing. Acetone: A smalll portion of residue was digested i n acetone for 20 minutes at 65 C. The mixture was f i l t e r e d and the f i l t r a t e was set aside. A yellow cr y s t a l l i n e material separated from the f i l t r a t e . The solution was decanted and used again to digest the residue; no crystals appeared on cooling the solution. Hydrochloric acid:The s o l u b i l i t y i n hydrochloric acid was s l i g h t , producing a yellow solution. Sublimation i n Carbon Dioxide. The behaviour of the brown precipitate when heated i n carbon dioxide, nitrogen, chlorine and hydrogen was next examined. A stream of carbon dioxide was passed over a small quantity of brown residue contained i n a porcelain boat(Figure 8). Part of the material sublimed with cautious heating and a blue deposit formed i n the condenser tube. The rest of the material turned black. The results of the preliminary test suggest a possible means of purifying platinum dimethylglyoxime. I f most of the brown material can be sublimed and i f the blue substance i s homogeneous and is the compound that we are seeking, then the p u r i f i c a t i o n of the Facing page I"• Figure 9 . Figure 10. Pyrogallol . Calcium chloride. 3. Potassium hydroxide. 4. Brown residue. (17) GOEroound should offer l i t t l e d i f f i cu l ty . The carbon dioxide treatment was repeated allowing ample time f o r a l l a i r to be removed. On w-arming the ignition tube the blue sublimate and black residue were formed as In the f i r s t t r i a l . Treatment with: carbon dioxide under pressure was also tr ied but the • black -residue was produced again. A resistance scoil was placed around the ignition tube in an attempt to get better temperature control and the work was repeated using carbon dioxide at atmospheric pressure and at reduced pressure. Treatment under reduced pressure was carried out in the following way. The gas was passed through the ignition tube for 30 minutes, the temperature was raised slowly, ifext, switch K (Figure 9) was opened and stopcocks A and B were closed, the generator was disconnected and stopcock C was opened to the pump. Vo change was observed. Then switch K was closed and the temperature was raised unt i l there was a puffing of the compound. A blue deposit formed on the walls of the tube and black material remained in the boat. Similar products were obtained in the carbon dioxide treatment at atmospheric pressure. The temperature was controlled in the last t r i a l by.-..closing and opening the switch at regular intervals. E i trogon treattaent (Figure 10 j . The brown material, when heated In an atmosphere of nitrogen, turned black without showing any sign of puffing. A gray body was left i n the boat after intense heating. There was, however, no blue deposit formed i n the condenser tube, A white film was produced ... Pacing page 16. Figure II . 1. Gone, hydrochloric acid. 2. Potassium permanganate. 3. Calcium chloride. 4 . Brown residue. (IS} on the walls of the ignition tube. Subsequent treatment of tlie gray body with hydrogen caused evolution of heat and the formation of considerable liquid within the ignition tube. The liquid turned anhydrous copper sulphate blue. Chlorine treatment of the brown residue. A preliminary test with chlorine produced explosively a black, material which did not change at a higher temperature. It reacted with hydrogen forming a gray mass. Platinum dimethylglyoxime was dried at 153 C . for 10 hours, weighed in a quartz boat, then treated with chlorine. A steady stream of the gas was passed along the train (Figure II) for ten minutes before any heat was applied. The temperature was raised slowly and after 10 minutes of cautious heating there was a puff and some material was discharged from the boat. The temperature was increased without any further change taking place. The tube was cooled after 15 minutes of intense heating. The black mass was treated with hydrogen for several hours. A gray body was formed which glowed on exposure to air. Weight of Ouarts boat 8,7521 g. Weight of boat and brown residue before drying 3 ,.9900 g. weight of boat and brown residue after drying 5.9700 g* Weight of brown residue I.2179 go Weight of boat and gray"body 9,24CI g. Weight of gray body 0.4030 g. Experimental percentage of platinum 40.47 A Theoretical value 45.69W ila) Ifr&ro;:ea treatment of the 'grown residue. A blue deposit appeared in the collecting tubs and the contents of the boat turned black.* At a higher tonperature tho blue deposit also becaa.e b l a c k s greatment of tho black material obtained fox heating ths- broru preci-oitate in carbon dioxide. Oarbon dioxide was passed over the material v;Lich remained in tho boat and heating was continued for 4?.- hours. The black material was partly decomposed to a gassy isass. Treatment of the blue deposit. The blue material,which c o l l e c t e d ia. the condenser tube, v/asr"-scraped into a porcelain boat, then It was treated ..1th chleriia..» Gentle heating produced a rapid reaction accompanied by a flash of light A black residua 'was left in the boat. aubseauent treatment with hydrogen gave a 0ray body. Discussion. The following suggestions arc offered as _.osrible explanations for the behaviour of the brown precipits.to wh.n subjected to the treatment outlined in the preceding group oaf experiment.s. The blue sublimate., 1 which formed in carbon dioxide, is probably pi;, tinum diw.wi'wl.vlyoxime, because It behaves in a manner similar to tia.t of nickel glyoxime when treated, first with chlorine - l^ber will i.rdrojv... It ...a: U.. either tk~ ^ 1 - t i u i u or ^ l^tiuous . . . . . . ^ w . i . - ^ u i v ' i . wj. uUu .Labia. •>CJ/L o .^UL. I J \ aj_,i !U - Mae X s s i a i . -"cix, i n h„ Iro^ e . If, I A J ^ _LV ' U " -'-c-^ipit^r i s pl.tl.ir -i , ' ^ l j i - , . . : , ^ , .g,u t : j bins deposit is more likely tke p la tinic: compound, live black residue which remains in tho boat may be either a decomposition product of dimethylglyoxime or of pletinuia glyoxime. If tho former as sumption Is correct, then the brown precipitate is heterogeneous. The puffing of the brown residue may be accounted for by assuming catalytic action of platinum.•Sufficient heat may be generated to volatilise part of the original substance, giving the blue deposit. The product obtained on passing chlorine over the blue substmice is probably a chloride, since subsequent treatment with hydrogen produces a g ,.s •which fumes in moist air. The same chloride may form on treating the brown precipitate with chlorine because the product reacts with hydrogen to produce the white fames and a gray body similar to that obtained with the blue substance. Ohloroplatinous acid with Dimeth:€Lglyaalma. R.h. Cooper (18j prepared platlnous dimethylglyoxime by reducing platinic chloride directly, then adding dimethylglyoxime to the platinous salt. In our investigation, 40 c.c. of chloroplatinic acid containing 1.86 grains of platinum was added to 85 c.c. of alcoholic solution of dimethylglyoxime containing 2.8 grams of tho glyoxime. The solutions were mixed at 65°C. and tho temperature was kept at this point for 15 minutes,then lowered to 45°0. The solution, which remained clear after two hours at this temperature- was removed from the water bath and left overnight at room temperature. The appearance of a brown crystalline precipitate was noted. Later, the u a j Cooper ' l l . i i . , J . y e t , d Liin» Coc. of a.A.. £ 5 , 2caa_7 (1325] (51) mixture was heated to 45 °C. and kept days, then'f i ltered, ana the residue I0°Ce at this temperature for several washed with 15 c.c. of alcohol at Solubil ity of Platinous Dimethylsl goxime. The solubi l i ty of the compound was tested at 60°G. in each of the following solvents* Solvent Solubil ity Acetone Slight Ethyl acetate Slight IF. butyl alcohol Insoluble Iso butyl alcohol Insoluble 1so amyl alcohol Insoluble Benzene Slight Chloroform Fair ly soluble Ethyl ether Insoluble Water Insoluble A solution of platinum glyoxime in chloroform was prepared by adding the platinum compound in small portions to 150 c.c* of the solvent. The mixture was kept at 58-60°C. for 8 hours and was shaken frequently. Recrystalliaation of Platinum Dimethylglyoxime. A saturated solution of the platinum compound was cooled slowly from 60 C. to room temperature, kept at this point for 16 h then cooled to zero°C. for 8 hours. Small crystals appeared at room ours (22) temperature and more material separated at sero'C. The mixture was not f i l tered because of possible contamination with dimethylglyoxime. Instead, the crystals were redissolved at 60 0, and the solution was cooled no lower than 50°0. F i l t rat ion through a Sooch crucible,at this temperature, left orange-colored crystals on the f i l t e r paper. -2hose were washed"with 5 c .c . of alcohol at I5°G, and dried slowly at room temperature. Professor 0.0. Swans on has kindly examined a specimen and finds that the crystal is orthorhombic, with smaller superimposed crystals imbedded in the faces of the larger crystal . Evidence for the orthorhombic symmetry is indicated by the perfectly centred interference figure. The angles between the faces and the axial ratios are shown in the diagram below: Facing page 23 Figure 12. Pyrogallol.. 3hlorine generator. Platinous compound. (23) Chlorine treatment of Platinous Dimethylglyoxime. The behaviour of the purif ied platinous compound when heated in chlorine and nitrogen was next examined. Crystals of the compound were spread out In a weighed porcelain boat and dried at I20°C. for 2 hours. The boat and contents were transferred' to a combustion tube and chlorine was passed over the crystals for one hour without any change except a slight tendency for crystals to decrepitate on warming. A tube, drawn out at one end, was inserted to collect any products lost from the boat. Chlorine was again passed through the tube and after thirty minutes of cautious heating the crystals were observed to vibrate and turn black. A few-seconds after this change there was a flash of l ight, followed by a puffing. A yellow deposit formed on the collecting tube and some . ... material discharged into the delivery tube. The yellow powder turned black when heated to a higher temperature in chlorine. Y/hite fumes appeared when dry hydrogen was passed over the black material, but no further change resulted on continued heating. nitrogen and Chlorine treatment. The following procedure was tried as a means of removing occluded air from the crystals. Nitrogen was passed through the ignition tube (Figure IX) to remove air from the apparatus. Stopcock A was closed and B was opened. Then a stream of chlorine was passed through the tube and the temperature wag kept: at .-20° G. ilext, nitrogen was passed, over the crystals and the temperature was raised slowly, causing slight decrepitation. F inal ly, chlorine was sent through the tube and the temperature was elevated. Only a slight r ise in temperature was needed to cause a rapid reaction, yielding products similar to those obtained In the i n i t i a l treatment. Reduction of Platinum Dimethylglyoxime to metal. 1 c .c. portions of platinum glyoxime solution were treated with the following reagents: Z% hydrogen peroxide, alkaline solution of sodium formate and alkaline solution of sodium oxalate. The hydrogen peroxide produced no change, but the formate and oxalate gave, in each case, a black f i lm at the interface of chloroform and aqueous solution. Partit ion of the yellow solute from chloroform to alkaline solution took place and the change was accompanied by a gradual darkening of the solution. Discussion; The crystals are evidently activated in chlorine at the time decrepitation starts since they turn black, then, after a short induction period, react explosively. This change may be brought about by the catalytic action of platinum. The yellow product and black residue formed in the chlorine treatment are probably the result of decomposition. They may be either chlorides or decomposition products of platinous dimethylglyoxime. (25) Chlorides and Oxides of Platinum. Chlorides and oxides were studied in a search for some compound which could be readily purif ied and would be suitable for .an atomic weight determination, but no suitable substance was found. A synopsis follows on methods of preparation and properties of these two types of compounds. Platinum tetrachloride was f i r s t obtained in an anhydrous state by v/. Pullinger (19), who passed dry hydrogen chloride over chloroplatinic acid at 165 C. The hydrated form of the tetrachloride was prepared by S.A. Norton by adding 2 moles of si lver nitEate solution to I mole of chloroplatinic acid and separating the platinum chloride by evaporation of the f i l tered l iqu id . H PtCl + 2AgE'0 ~? 2AgCl f 2IIO + PtCl . 2 6 3 3 4 Dehydration of this chloride gives the anhydrous salt(20), which on heating above 350°C. dissociates to form progressively the tr ichloride, dichloride and metal. P.C. Phi l l ips(2l) observed that hydrogen reduces solid hydrated platinum tetrachloride below 80 C. with evolution of water and hydrogen chloride. (19) Pullinger \7., J . Chem. Soc. 61, 423 (1892) (20) Hellor, Inorganic and Theoretical Chem. XVI. 292-6 (1937) (21) Ph i l l ips , P.C., Am. Chem. Journal 16, 255 (1894). (26 J ' Yoorhees and Mams obtained platinum dioxide(22) by fusing a mixture of ohloroplatinic acid and sodium nitrate at 300 0. Iv:cldinney(23) prepared the oxide by the same method, then reduced i t with carbon monoxide. An explosion occurred after an induction • period of several hours at room temperature. At higher temperatures there were shorter induction periods, but the transition from slow to rapid reaction always took place quickly. Adams and Slrriner (24) reduced the oxide with hydrogen, producing metallic platinum. TJellor refers to the works of von Meyer and V/ohler, in discussing the reduction of platinum dioxide by hydrogen. The former observed that hydrogen reduces platinum dioxide energetically at ordinary temperatures. He also found that a hydrate, PtO »H 0, aan be 2 2 prepared from platinum tetrachloride by evaporating to dryness a mixture of the salt and excess sodium carbonate, v/ohler observed that hydrogen reduces this hydrate at s l ight ly elevated temperatures, (22) Yoorhees and Adams, J . Am Chem. Soc. 44, 1397 (1922) (23) McKInney P.V. ibid 56,2577 (1934) (24) Adams and Slrriner ib id 45,2171 (1923) (2?) 'Suisaaryt The results of this investigation say he summarised br ie f ly as follows; 1. Ohloroplatinic acid reacts with dimethylglyoxime to form an insoluble and fa i r l y stable compound, which can be reduced to metal by treatment, f i r s t with chlorine and later with hydrogen* It is a problem,, however, to get a suitable method of purifying the material, 2. Chloroplatinic acid can be reduced _ito chloroplatinous acid by sodium oxalate» 3„ Platinous dimethylglyoxime can be prepared In purif ied form by recrystal l ization from chloroform solution. The transparent orange-brov.11 crystals exhibit orthorhombic symmetry. 4. The crystals decrepitate when heated in nitrogen, and subsequent treatment with chlorine produces a rapid reaction accompanied by the discharge of a yellow material and the formation of a black residue. 5 . Alkaline solutions of sodium formate or sodium oxalate reduce platinous dimethylglyoxime to the metal. Acknowledgment» The writer wishes to express, sincere thanks to Dr. E.H. Archibald for the loan of materials and apparatus and for his many helpful suggestions. .Bibliography (26) 1, Adams, 3. and Kamm, 0., "Dimethylglyozime" , J. Am. Ghem. Soo., 40, 1281-9,(1918). 2. Adams, R. and Slrriner, R.L., "Platinum Oxide as a Catalyst in the Reduction of Organic Compounds", Ibid, 45, 2171, (1925). ,3. Archibald, Z.H. , "The Atomic Weight of Platinum", Proc. Roy. Soc. Edin., 29, 722-747, (1909). 4. Aston, F.W., "Mass Spectra and Isotopes;' (1933). 5. Brunck, 0., "Use of Dimethylglyoxime for the Determination of III eke 1", Z. Angew Chem. 20, 3844, (1907), Ghem. Ab. 2, 240,(1908). 6. Brunck, 0., " A Hew Method for the Quantitative Determination of HIckel", ib id , 20, 384, (1907), Chem. Ab. 2, 46,(1908). 7. Gongdon, L.A. and Beige, C.II., "Cr i t ica l Studies on Analysis of Hickel", Chem. Hews, 128, 67-8, (1924). 8. Cooper, R.A.,"Hote on Platinum and Palladium Dimethylglyoximes", Journ. of Chem., Met., and Min. Soc. of South Afr ica, 25, 296-7, (1925) 9. Halm, 0., "Die Ohemischen Elements raid naturlichen Atomarten nach dem Stande der Isotope und Kernforschung", Ber.7I, I, (1938). 10. Hooley, J .G. and Phi l l ips , H.W.F., "A Convenient Water S t i l l " , J . Chem. Educ., II , 376, (1934). II• Hopkins, B.S., "Chemistry of the Rarer Elements." 12. Mellor, "Comp. Treatise on Inorg. and Theoretical Chem." Vol. XVI. 13. MoKiffiiey, P.V., "Reduction of Platinum Oxide by Carbon Monoxide", J . Am. Chem. Soc., 56, 2577, (1934). 14. ITuka, P., "Zur Loslichkeit des • Hickel dime thylglyoxims", Z. Anal. Chem., 91,29-32, (1932). • (29) 15. Foyes, V,AA„ said Weber, H.3.?., "Atomic T.rei_::f of ehlorire", BuH.. U.C. Bureau of Stand. , 4, 347 (i:t7_; ? 16. Parr and Lindgreu, "Data, of aiohol da. '.a^a'j Trans, Am* Brass Pounders' Assn. 5, 120-9. Civ.-... .'a, 20, 6:IeT55 17. Phillips, ?.C., /sii, Chem. Journal. 16,1;^ , (xJA-i } "laeseaicues upon Phenomena of Oxidation and Chan, jnvps. of Gases". . " " :. . . "Platinum Tetrachlcrido", J» Chem. ?oc. 61,423 (IC92 ). " _ j „ . - Pleakiiers "Kelativo Abundance of Isotopes of Ian. 50bs ?t, Pds Ir , 3h, Co", Phy.Pev, 50, 734 (1936) 20. Thompson, 3.0., Beamish F,B,, Scott ,M., " Detn. of Cold and Platimmi and Detection of Pt metals", J . Ind. nail aie;, Chem. Analyt. Pd, Sept, 1937, 21, T T.:". Bureau of Standards, "aodium Oxalate as a Standard In Volumetric Analycis", Giro, Fo,58I, Feb 20, 1950, 2a, Yooahsea and adorns, "Oxides of Platinum for Reduction of Organic Compounds", J. ha, Chem, Soc5 44, 1597 (1922). 25. AAhor PAC,P.>4 "Prep, of Chloroplatinic acid \yj Electrolysis of ? I u t i i ' - . t u V.Z* Bureau of Stand. , Bulletin t, 36a, (1907-8) 


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