摘要:

The Faradq Society is iiot rcsPotisible for opiiiioizs cxpiassed before it by Auiliors OY Speakers. OF F O U N D E D 1903. TO PROMOTE THE STUDW OF ELECTROCHEMISTRY, ELECTROMETALLURGY CHEMICAL PHYSICS, METALLOGRAPHY, AND KINDRED SUBJECTS. VOL. v. FEBRUARY, 1910. PART 3 . ON THE ELECTROANALYTICAI, DETERMINATION OF LEAD AS PEROXIDE. BY HENRY J. S. SAND, PH.D., D.Sc. ( A Pafier rend bcforc the Faraday Society, Tuesday, hi'oveinbev 30, 1909, Mr. JAMES SW~~BURSE, F.K.S., President, irz the Cltair.) The electroanalytical determination of lead as peroxide has hitherto been rendered somewhat uncertain by the fact that when dried at temperatures at which it may be considered to be free from the risk of decomposition, it is always found to retain a small amount of water, and the corrections which various investigators state should be made for this vary very considerably.It has therefore been proposed by Treadwell ::: to ignite the peroxide at a dull red heat, and thus convert it into. oxide. This suggestion can, however, be carried out conveniently only when a dish is employed as the anode. Where gauze electrodes are made use of, it has been found practically impossible to effect the conversion in a gas flame without at the same time obtaining some lead as metal, owing to the reducing action of the flame. The theoretical factor for the calculation of lead from peroxide is 0.866, and the experimentally found factors which various investigators have put forward vary between 0'8j3 to 0'857 according to Hollard and Bertiaux,t and 0.8634 to 0.8643 according to R.0. Smith,: and also according to Arthur Fischer and V0ssen.s The resblts thus differ from the theoretical value according to the investigator, by amounts varying between 0.15 and 1-5 per cent. The slight variations found by the same investigator refer to different amounts of lead. The temperatures for drying are given variously by the different investigators as zoo0 and 200° to 230°, but it may be considered certain that the discrepancies are not due, in the main, to difference of temper at ur e. The following experiments were carried out primarily with the view to elucidate the behaviour of a lead peroxide deposit on drying, and incidentally further to study the effect of varying conditions on its nature generally. * Aizalytical Chemistry, vol.2., p. 140 (New York, 1904). t Analyse par Elecfu-olyse, pp. 72 and 173 (Paris, 1906). ; Jouria. Amcr. Clrcnz. SOC. 27, 1287 (1905). S Arthur Fischer, Elekiroalzalytische Scltnellunehodeii, p. 174 (Stuttgart, 1908) ; or Classen, Elckfroannlysc, 5th ed., p. 12 j (Berlin, 1908).The ci~~cun~stances controlling the coherence of thc peroside haw been found very similar to those which govern the cohcrence of metal deposits. The higher the temperature and the smaller the current density, the more coherent is the precipitate. When employing the conditions which are iiiost favourable to the quality of the deposit it is, however, necessary to avoid too large an amount of nitric acid in thc electrolyte, and it is specially important to remove any oxides of nitrogen which may be present by evaporating the electrolyte to dryness before a determination.Even small quantities of these osides will render the eshnustion of the electrolyte at high tempera- tures impossible. The temperature was always kept slightly below the boiling-point, a masimum of about 97" never being esceeded, as the current appears to produce lower osides of nitrogen from the nitric acid at 100". Large quantities of ammonium nitrate appear to render the precipitate of peroxide loose. It is not improbable that, under suitable conditions, alkali plumbates, and even the plumbates of heavy mctals, may sometimes be formed as intermediate products.:: Colloids appear to havc a similar effect on the deposits of lead peroxide as on those of metals. When obtained from a solution in which a small amount of stannic acid in the colloidal state is present, the precipitate of lead peroxide is always much more coherent than it would otherwise be.Small amounts of the colloid are precipitated with the peroxide. This fact should also be borne in mind when a solution is to be electrolysed in which colloidal metal oxides may be produced by the hydrolysis of salts.+ In almost all the experiments to be described, the electrolyte coiitained only nitric acid beside the lead salt. In two or three a small amount of nitric acid and a very large amount of copper nitrate were, however, added in conformity with a suggestion by Hollard and Bertiaux.: The method was, however, not proceeded with further, as it suffers from the fact that the electrolyte cannot be conveniently tested for freedom from lead, and besides, the results were found two or three tenths of a per cent.higher than with the strongly acid electrolyte free from copper. The electrodes employed were those previously described.$ The outer electrode was always the anode. The gauze covers a surface of about 50 to 55 sq. cm. It consists of about 14 wires per linear centimetre of approxi- mately 0.2 mm. diameter, and the total surface available for the peroxidc is probably somewhat less than yo sq. cm. The volume of the liquid was about 85 C.C. The exhausted electrolyte was always tested for absence of lead by neutralising a sample with ammonia and adding hydrogen sulphide, and the cathode was also examined for freedom from lead. In a former paper I! the author gave some results for the determination of lead as peroxide.The theoretic;il factor was employed, and both positive and negative deviations were obtained, the former seldom exceeding 0.3 per cent. The details of the method of drying, which were at that time not given, may here be stated. An oven improvised from a I+-litre Jena beaker, protected at the bottom by asbestos paper, was employed, which was covered by a cork lid, and a current of air was drawn through by means of a water -pump. In the course of the present investigation it wasisooii found that at a * This may explain some of the abnormal results recently obtained by G. t See preceding note regarding Vortmann's results. 1 LOC. cif., p. 71. 5 Tvairs. Faradny SOC. V. 159 (1909), and Tmns.Chcrit. SOC. 93, I j j 2 (1908). I( Traits. Client. SOC. 91, 397 (1907). Vortmann, A m . Cheirz. 351, 283 (1907).OF LEAD AS PEROXIDE 309 temperature of about 20o0 a lead peroxide deposit is capable of absorbing moisture in a damp atmosphere, and only parts with this exceedingly slowly when heated in carefully dried air. The apparatus employed for heating in a moist atmosphere consisted of a sheet-iron can of about 25 cm. height and I I cm. width, which was closed at the top by a cork. The latter was provided with an opening designed to hold a smaller cork, to which thc electrode was suspended by a wire. Some water was evaporated at the foot of the can, which contained sufficient openings to allow the steam to escape, but was devoid of any arrangement to produce circulation of the atmosphere.The distance of the electrode from the bottom of the can nas about 10 cm. In the experiinents the electrode was always removed from the can while hot, so that there might be no possibility for drops of water to condense on it on cooling. For those experiments in which the electrode was to be heated in dried air, a copper cylinder of about 25 cm. height and j cni. diameter was employed. The bottom was brazed on, and the top mas closed hermetically by a cork. An altogether unexpected difficulty was experienced in obtaining a flawless cork of the necessary diameter cut at right angles to the grain, which would fit gas-tight. This difficulty was only overconie by obtaining a cork cut froin a composite piece, consisting of three parts glued together.The cork held two glass tubes by means of which air previously dried in a tower containing caustic potash and calcium chloride could be caused to circulate with the aid of a water pump. In one experiment the electrode, with about 0.37 gram of lead peroside, was heated to 200Oin the moist atinosphere for 25 minutes, whereupon it gained 1.1 mg. in weight. On further heating in the dried air for j o minutes at ISOO, it lost 0.5 mg., and on again heating in the dry air for over an hour, it lost 0.3 mg. After this it increased in the moist air at zooo in 13 minutes by 3 mg., in another 20 minutes under the same conditions by 1-3 mg., then again in 35 minutes by 1.5 mg., then in 20 minutes by 0.4 ing., and in mother 20 minutes by 0.8 mg., making a total increase of 6 nig., i.e., of about 1.7 per cent.After this the increase on further heating was inappreciable. The heavy deposit thus obtained only parted with its water esceedingly slowly when heated in the carefully dried atmosphere. In 20 miniites it lost 0.8 mg. at about 2100, and even at much higher temperatures the decrease was very slow, thus the loss in an hour at 230° to 240° was only 0.6 ing., and at about 2800 in an hour and a half it was ~ ' 4 ing. These experiments show that in drying the peroxide it is specially important not to allow it to absorb water from a moist atmosphere at a high temperature. They furnish a quite sufficient and satisfactory explana- tion why different investigators should have obtained different results when special precautions were not taken to remove the moisture from the atmo- sphere of the drying oven.At a minimuin temperature of about 3300 it appeared that even in a damp atmosphere no appreciable increase took place, but attention must here be drawn to the impossibility of heating an object of j or 6 cm. height uniformly in an ordinary drying oven. A difference of 200 to 30'' must always be allowed for between the hottest and the coldest parts of the object. Drying at a maximum temperature of 300" was also tried, but it appears that the peroxide is not absolutely stable at these high temperatures and that a continual decrease in weight takes place. The author believes that it may be taken as certain that when lead-peroxide is in contact with air, there is no true equilibrium which would condition the existence of a definite temperature of decomposition, i.e., a temperature at which the decomposition tension of the peroxide would be equal to the210 OK THE ELECTKOANALY'TICAL DETERMINATIOK PbO, found. partial pressure of the oxygen contained in the atmosphere.We are, on the contrary, here no doubt dealing with a so-called false equilibrium for which it would be exceedingly difficult to state definite conditions of stability. All these circumstances will always tend to make the drying of the peroside at high temperatures a somewhat uncertain operation. The best conditions are no doubt to take the deposit quickly up to a temperature of about 230° in a current of dried air. The factor which was found at B temperature of 200" in dried air varied between 0.863 and 0.865.A iiiuch more simple and probably also more certain method to obtain satisfactory results was afterwards discovered in adopting the identical procedure always made use of for metals, viz., to dip the electrode first into a jar containing alcohol, then into another containing ether, and then to dry it rapicllv over a Bunsen burner. The electric current itself is made use of to keep the deposit free from water by electric endosmose. The conditions for securing a satisfactory result arc a high temperature of the electrolyte and R high current density.';' A special experiment showed that a lead perosidc precipitate does not absorb water so rapidly that an increase of weight need be feared during the operations of disconnecting.The electrode with a dried weighed precipitate of 0.4600 gram lead peroxide was dipped into water and dried wit11 alcoliol and ether. The operations were repeated, and in both cases no change of weight was observed. It was likewise shown that no error need be feared if the ether should burn for an iiistaiit after accidental Factor Time. hf inutes. Temper;ittirc. Aniperes. 0.3668 0.3690 0.3695 92-95" 5 65" 5 40" 0.7 I 2 20 9 I d n 3 4 2 7 Y 9 1 0 I 1 I" Pb taken 0.3194 0.3882 0.3970 0.3656 0.3626 0'3830 1'0200 0'95 I00 0*95100 1'0232 1.0847 01214 PbO, fOlll1d. 0.3699 0.4499 0.4600 0.4228 0'443 1 1.1794 1-1007 1.2 542 o' 1407 0'420.5 1'1022 I ' I s y Amperes. 5 5 5 5-10 5 5 5 5 3 5 5 5 Temperat tire. 90 90 93 92-95 92-97 9-97 9-17 95-97 95-85 95 97-80 96-75 Time.hIinutea. I 0 9 15 I -5 35 17 9 - I2 20 20 20 Factor. 0.8635 0.8629 0.8630 0.8647 0.8644 0.8623 0.8649 0'8627 0%40 0.8649 0.8648 0.863 * The dehydrating action of the current by electro-osmose especially at high temperatures has been inade use of for the dehydration of peat ( H W s f e r Fnrh~~crke D.K.P., 179,983 kl. Sza. >UKI D.K.P. 1Sj,189 kl. 82a.OF LEAD AS PEROXIDE 311 ignition during the process of drying. The effect of varying coiiditioiis of temperature and current on the weight of the precipitate is shown in Table I. A measured quantity of solution containing 0.3 172 gram of lead was taken for each experiment, the amount of nitric acid was 10 C.C. per 85 C.C. solution. Small currents were taken at the low temperatures in order to obtain ;I coherent deposit and to avoid the precipitation of lead on the cathode. Table 11. gives a summary of the results obtained under slightly varying conditions. In all the experiments, except Nos. 7 and 8, metallic lead was started from and the solution was quite free from oxides of nitrogen as already explained. The amount of nitric acid present was always 10 C.C. and the volume of the solution 85 C.C. The results may be summarised as follows. For a temperature of about 90" and a current strength of 5 amps. with the electrodes described the factor 0.863 may be taken. For a teni- perature of 95" to 97" the factor is 0.865. In either case when alloys are analysed in which the percentage of lead is not very high, it will no doubt be sufficiently accurate to employ the theoretical factor 0.866. The amount of peroxide deposited does not appear to have any definite effect on the value of the factor. The expense of the foregoing investigation was iiiet by grants froiii the Government Grant Committee of the Royal Society, and from the British Association, for which the author desires to express his indebtedness. UNIVERSITY COLLEGE, NOTTINGHAM, Septeirtber, 1909.

ISSN:0014-7672    

DOI:10.1039/TF9100500207

出版商:RSC    

年代:1910

数据来源: RSC

摘要:

OF LEAD AS PEROXIDE 311 DISCUSSION. Dr. F. M. Perkin said he had recently been making a large iiuiiibcr of lead deternlinations, and from his experience lie agreed with the author that the presence of excess of oxides of nitrogen in solution made it impossible to get accurate results. He imagined, however, that as a rule the coiiditioiis employed would be those advocated by the author, so that 110 moisture might appear on the deposit. Dr. Sand showed clearly why it was necessary to adopt his methods, namely, rapid washing and the use of alcohol and ether in drying. In reply to the Chairman, Dr. F. M. Perkin, in thc absence of the author, said that although alkali solutions gave very fair deposits, these were not adherent but exfoliated. Moreover, it was difticrilt to get rid of the alkali.

ISSN:0014-7672    

DOI:10.1039/TF9100500211

出版商:RSC    

年代:1910

数据来源: RSC

摘要:

OK THE INFLUENCE OF DISSOLVED GASES ON THE ELECTRODE-POTENTIAL IN THE SYSTEM SILVER- SILVER ACETATE, aq. BY ARTHUR JAQUES, B.Sc., late Fellow of Armstrong College, new castle-on-Tyne. ( A Plrfcr read beforc the Fnraday Society, Tiresday, Nomnbcr 30, 1909, Mr. JAMES SWNBURNE, F.K.S., PRESIDEST, i l l fizc Chair.) It has been shown by Brislee::: that concordant values for the e.m.f. of the cell Ag I AgC,H,O,,xN I NH,NO, sat. I 0'1 N. cal. electrode at 18" can be obtained by boiling out the water before making up the silver acetate solu- tion and carefully excluding air from the solution ; and the values obtained in this way when corrected for the concentration Bgrec well with those for the corresponding cell containing silver nitrate. As the complete esclusion of air from the solution appeared to present some difficulties, measurements were undertaken in order to see whether the same effect could be obtained by blowing an indifferent gas through the solution until the wholc of the foreign gases should have been espelled.For this purpose the apparatus shown in the figure on p. 218 was used. It consists of the vessel A in which the solution is placed, and the side tubes €3 and C, by means of which the gas enters and leaves respectively. Contact with the ammonium nitrate solution is made by means of the tube K. The apparatus is clamped in position by a cork passed over the tube C. The electrode D is held in two brass bearings E and F, thus allowing of its being rotated. It consists of a glass tube through the ends of which pieces of platinum wire are fused.These are joined by a copper wire inside the tube. Contact is made by means of mercury in the cup G, and the entrance of air into the vessel X is prevented by means of the mercury seal H. The e.m.f. was measured with the aid of a Crompton potentiometer. A cadmium cell which had been standardiscd at the National Physical Laboratory was used as standard. As a null-instrument a galvanometer capable of indicating IO-'" ampere was employed. All measureinelits were made through the closed taps of the electrode vessels, and an external resistance of IOO,OOO ohms was usually kept in the circuit. An analysis of it is given in the nest paper. The silver acetate used was obtained froin I<ahlbaum. X number of the ineasureiiients of the cell- Ag I AgC,H,O, sat. 1 NH,NO, sat.I 0.1 N. cal. electrode, made without precautions to exclude air, showed that for a given cell thc c.11i.f. sometimes varied about 10 millivolts in two or three days, and the values for different cells made up in the same manner varied to the extent of about 30 millivolts. * I'roc. Fnrrrri. SOC., December, ic)oC\;. 313THE IXFLUESCE OF DISSOLVED GASES 2 r3 It was found that the variations were coiinected with the quality of the distilled water, and were due to the presence of dissolved gases in it. The electrodes used were of two kinds, viz., (a) platinum wires electro- lytically coated with silver from a potassium silver cyanide solution, and (b) silver wires. The latter were fused through the end of a glass tube with fusible glass, the tube was filled with a mixture of beeswax and resin, and a little of the same mixture was poured on to the outer junction between the glass and the silvcr.The wire was cleaned from time to time by simply scraping with a knife, and it was found that on substituting one kind of electrode for the other in the same solution, the difference never exceeded 1.5 millivolts, save on one occasion when the difference was 15 millivolts, and indicated a defect in one of the electrodes. In all the measurements in which gases were blown through the solution, only electrodes of the first kind were used. The solution was usually prepared by shaking the salt with water in the electrode vessel for ;I few minutes, until a quantity of wet crystals sank to the bottom on standing.Solutions prepared by shaking the salt with water for 24 hours in the thermostat gave similar values. Table I. shows some of the values obtained. In all the measurements-Nos. 5-12, the potential reached a fairly constant value between 0.3 j 3 and 03 57 volt. A saturated solution of silver acetate at 25" contains 0.0664 gram equivalent per litre, and its equivalent conductivity was found to be 75'2.': Calculating the value of A, from Kohlrausch's values for the ionic conductivities and their temperature coefficients, we find Jl = 101.5, whence- If we take the value 0.354 for the potential of the cell Xg I AgC,H,O, sat. 1 NH,h'O, sat. [ 0.1 N. cal. electrode, we find for the potential, if the silver ion concentration were normal, using the Sernst forinula- Taking the potential of the 0.1 N. cal.electrode at 25' as 0.618 volt, we find for the E.P. of silver the value 1.049 volt. This value differs widely from those found by G. N. Lewis j- and by Brislee, :: but agrees very closely with the mean value given by Wilsmore in his table +namely, 0.771 volt (H = 0 at 18'). From this, assuming the E.P. of hydrogen at 18O to bc 0'277 volt, we obtain E.P. Ag at 18" = 1.048 volt. As Wilsmore's value rests upon a large number of measurements by different observers, the eight values for the cell lying between 0.33 and 0.357 volt and many others not in the table might have been regarded as admissible save for the unexplained deviations from this value in the earliest measurements. Mensu rerrteitis dirriiig ilie Passage of Gases through the Solution.-The hydrogen used was generated in a Kipp's apparatus from commercial " arsenic free " zinc and '( pure " hydrochloric acid.It was passed through three large U-tubes filled with broken glass, moistened respectively with lead * See nest paper. : LO(.. Cii. t Zcit. I'll-ps. Cliein., 55, 1906. $ Zcit. Plzj's. C h e w , 35, 1900.INFLUENCE OF DISSOLVED GASES Measurement. I I 8 9 10 I1 12 13 14 1 .i 1 0 P.D. 0'369 0368 0'363 0372 0376 0.376 0'355 0355 0.353 0.361 0.3585 0356 0 3595 0361 0.3625 0.354 03% j 03613 0.364 0'35.1 0349 0348 0'347 0.353 0.351 0.356 03-53 0'349 0'355 0355 0'357 0'356 0.356 0354 0354 0.359 0'355 0355 0.362 0361 0357 0.3780 03780 0.3830 0.3860 03S85 0'3805 0.382 0 3835 03795 03810 03705 0.3680 0.3685 03% 0.36% 03765 03765 0.3760 0'3753 0'374 0.373 03525 0.3700 0388 j 03710 TABLE 1.Time. 0 3 hours Gext day next day 2 days later 0 0 14 Ilours 4 * I 24 ,1 275 .I 29: ., 72 ,. 0 .; hours 7 ,* 50 ,, 30 ininutes 0 I hour 6 hours 2 1 , I 30 minutes 0 Remarks. } Silver wire electrcde. } Ditto. Ditto. Silver wire electrode. One or two drops of glacial acetic acid added. Ditto. Solution made up with a little acetic acid and shaken overnight in the thermostat. Silver wire electrode used. Ditto. Icscess of silver acetate added, so that the electrode was completely im- mersed in crystals. Soioliitioii shaken in thermostat. Acetic acid present. Silver wire electrode used. Silvered platinum electrode suhsti- t .I tutcd for silver wire. Solution shaken in thermostat } Acetic acid present. After adding a drop of glacial acetic Silver wire electrode. acid.Uter introducing a new electrode. Silver wire electrode. <lectroIytically coatcd plntinuni wire electrode. Electrode rotated. t i I Electrode rotated.13 I h) % rn a E 5 (r9 * 5 5 P. CT x 5 p216 Measurement, 2 (cortt. 3 4 5 6 INFLUENCE OF DISSOLVED GASES TABLE 11.-continucrl. Temp. 25" P.D. 0.3798 0.3788 0.368 0.367 0362 0.360 0.3585 0.363 0.3680 0.3748 0.3783 0.3780 0.380 0.3830 0'3835 0383 j 0.356 0'353 0'350 0.348 0.350 0.376 0'3750 0'3757 0'3767 0.3770 0.3.9j 0.3628 0.3640 0.3630 0.360 0.3770 0-3Soa 0.3806 u.3810 0'377 0.3665 0.3642 0.3662 0.3675 0.3683 0.381; 0.3820 0.3827 0..;840 0.3838 0.8823 0'.3837 0'3735 0.366 j 0.3639 0.36 jo 0'3743 o..;c) 14 0.3825 0.3780 0.3815 0'348 0.3 j I Time.24 hours 18 m. later - .j miis. 1.5 11 16 11 21 1 7 55 * l 71 11 96 1 1 178 11 I93 11 233 17 247 v 253 1 - 258 , l 277 1 9 280 1 , 309 11 319 11 3.35 11 341 ' 1 370 1 1 394 11 43: 91 53h 11 23 hours o mins. 6 1 1 9 11 2 1 11 41 1 9 90 11 117 7 1 148 17 176 11 1 8 - j hours o inins. 1 0 11 33 -- 7, 55 l l 6s , ) 257 1 l 313 91 Remarks. Hydrogen blown in. Hydrogen blown in. CO, blown in. H, blown in. Flow of H, stopped. Apparatus closed. Electrode rotated. H, blown in. Apparatus closed. Electrode rotated. Rotation stopped. Hydrogen blown in. Apparatus closed.ON ELECTRODE- POTENTIAL 2=7 hf easurement. 6 (COllt, 7 8 9 Temp. 35c TABLE I1 .--coiitiiined. P.D. 0.jSLp 0.3 j6 0.360 0.357 0.3 580 0.3575 0.3600 0 ' 3 j I j 0.3730 0.3769 0.3790 0.366 j 0.3618 0.3737 0.3790 0.3809 0.3818 0.3814 0.3625 0.3700 0'357.5 0'3535 0'3475 0.380; 0.3820 0.3825 0.3835 Time.2 2 - j hours o mins. 140 11 20 hours 26.5 ,, 14 91 92 9 1 6-5 11 23 9 1 18 mins. 30 11 73 ? l 119 I ? 117 11 236 1 , 331 :1 0 11 27 ,, 290 ,. 22 hours o mins. 3 hours 4 mills. 1.59 11 31.3 ,* 401 1 1 24 l1ours Remarks. Control experiment. Potential rose gradually. Electrode rotated. Hydrogen blown in. Time counted from the last reading. Hydrogen blown in. Time counted from the last reading. Apparatus closed. nitrate, silver acetate, and caustic potash solutions. The gas was then bubbled through a wash-bottle containing water. The same absorption apparatus was used for oxygen, nitrogen, and carbon dioxide, save that in the last case the potash tube was cut out. The nitrogen was made by dropping a strong solution of sodium nitrite into a \varni saturated solution of ammonium chloride.Osygeii was obtained from an ordinary Hrin's cylinder. Carbon dioside was generated in a Kipp's apparatus from marble and 1iydrochlo1-ic acid. The measurements were intended to be only comparative. The oxygen and nitrogen probably contained small quantities of other gases, but the hydrogen and carbon dioxide were probably fairly pure. The chief sourcc of impurity mas most lilicly the incomplete washing out of the absorption apparatus, and of the Kipp's generators. On hlowing in hydrogen the potential fell rapidly, then slowly rose, and finally became constant after threc or four hours, giving the value about o'j83 volt. Some of the values found are given in Table 11.Each gas was blown through until the P.D. remained constant for nearly an I~oiir, with the exception of hydrogen in measurement 2. In this measurement the passage of the gas was stopped when the P.D. was still about 6 milli- volts below the constant value obtained in the previous case. On the following day the potential had risen about 1 . j millivolts, but on passing i n hydrogen it did not rise further. 011 passiiig hydrogen through a silver acetate solution a deposit of silver218 INFLUENCE OF DISSOLVED GASES forins slowly on the glass vessel. This must cause a slight alteration in the concentration of the solution. Further measureinelits show that the potential nevertheless attains a fairly constant value. The change of con- centration necessary to affect the potential by I millivolt amounts to 4'4 per cent.Attempts werc made to saturate the water with hydrogen before making up the solution. Some distilled water was boiled vigorously in the wnsh- bottle, hydrogen being passed in during the boiling and subsequent cooling. The water was poured into a bottle filled with hydrogen by means of a tap- funnel, the hydrogen being allowed to escape by means of a tube with a tap in it passing through the stopper. The bottle was provided with a tap outlet at the bottom, and was kept in connection with a Kipp's apparatus containing arsenic-free zinc and hydrochloric acid. Three large U-tubes were inserted between the bottle and the generator, containing respectively lead nitrate, silver sulphate, and caustic potash solutions.This water was drawn off into the electrode vessel, solid silver acetate was added, and the vessel was placed in the thermostat. The electrode was introduced and the mercury seal closed, and hgdrogcn was passed through K A U for a few minutes in order to remove the air. The electrode was rotated in order to stir the liquid, so that the concentration might quickly rise far enough to make the potential practically that of a perfectly saturated solution. The potential measureinelits with this solution are giveii in Table II., No. j. As the potential did not differ from that obtained when much air was in solution, and did not rise considerably in an hour, hydrogen was blown in. The potential soon rose to the value obtained in former measurements, and it is noticeable that in this case there was no preliininary fall such as always occurs when hydrogen is blown into n solution containing air, and especially carbon dioxide. Another measurement made with the hydrogen-saturated watcr gavc the results shown in No.6. The water was stirred with excess of silver acetate in an atmosphere of hydrogen. The stirring was stopped when a quatitity of the salt had sunk to the bottom of the vessel. Hydrogen was not blown through the liquid during measurement. In this case the potential actually fell at first, then gradually rose to about the same value as before. The rise is slow, but evidently will occur without actually blowing in the gas. At theON ELECTRODE-POTENTIAL 3 19 close of the ineasurements a very slight deposit of silver was found on the tube carrying the electrode.No. 7 shows the result of a control measurement with water which had stood for some days in contact with the air. The values are in good agree- ment with the original values in Table I. The potential did not rise notably on standing. As before, the electrode was rotated for a few minutes before tlie measurements were begun. Fairly constant potentials having now been obtained by blowing hydrogen through the solution made by simply stirring the salt with water in the electrode vessel, it becanie desirable to see whether previously shaking the mixture in the thermostat would affect the result, i.e., whether the solutions previously used might be treated as strictly saturated. Excess of silver acetate was shalten with water for 48 hours at zs0, and some of the solution together with excess of the solid salt was placed in the electrode vessel and tlie potential measured.The results are given in No. 8. On blowing in hydrogen the potential fell in the normal manner, and then rose to the ordinary value. In nieasurements 5-8 the electrode vessel was coloured by coating it with a solution of Bismarck brown in a mixture of collodion and alcohol. The solvents dried off quickly, leaving an insoluble and deeply coloured skin adhering to the glass. The exclusion of light does not affect the final value obtained on blowing in hydrogen, nor, apparently, the low value obtained with solutions containing air, nor does it prevent the reduction of the silver acetate by hydrogen.':: There is thus no doubt that the low potentials obtained with some satu- rated solutions of silver acetate are due to the presence of dissolved air in the solution.Shaking the salt with water in the electrode vessel suffices to saturate the solution within the other limits of error of the potential measure- ment. Concordant but different values can be obtained by blowing hydrogen, oxygen, nitrogen, or carbon dioxide through the solution. The values for nitrogen and oxygen in the measurements made were equal. By using a constant supply of water, e.g., water which is saturated with air, concordant values can be obtained which differ by nearly 30 millivolts from the correct va1ue.f Rotating the electrode has no noticeable effect upon the final values obtained on blowing in hydrogen.X series of measurements was made with 0.05 N. silver acetate, using hydrogen and carbon dioxide, with precisely similar results. Here the question of saturation does not enter. The final values obtained on passing hydrogen will be given later. On one occasion during the measurements the potential varied in an erratic nianner over a range of a few millivolts. It was found that the tap of one of the electrode vessels was in contact with water of the thermostat. This indicated a leak over the surface of the glass of the other vessel, for if the insulation had been perfect no effect should have been produced. A copper wire was attached to one of the connecting wires and allowed to dip into the water of the thermostat. The other wire was connected to a caloniel electrode.On pressing the key (with IOO,OOO ohms in the circuit) a large deflection of the mirror was observed. To remedy the error which might possibly have been introduced in this way, a layer of ca. 7 cms. liquid * A little white light would enter the vessel by the side tubes, which were not cmipletely coated. t See the results with silver nitrate. The exclusion of light was therefore not quite complete.220 INFLUENCE OF DISSOLVED GASES paraffin was poured on top of the water, as recomniended by Coggeshall.'.' The iiisulation was then found to be perfect. A number of the measurements made previously were repeated, but no difference was found either in thc general behaviour of the potential during the passage of the gases or in the final values obtained.The error may therefore be neglected, and indeed showed itself at once in the one case where it was considerable, by the erratic movements of the potential. The temperature of the paraffin was always 2-3O below that of the water. It rose, however, on stirring, aiid the temperature depended upon the speed of stirring. It W;LS found that the temperature of the paraffin was higher towards the bottom of the layer than at the surface. By moving the thermometer about differences amounting to ca. 0 . 3 ~ could be obtained. The thermoineter was kept resting upon the stand on which the vessels were placed, i.e., near the hottoin of the paraffin, so that the readings are probably slightly higher than the true temperature of the liquid in the cells.It would be difficult to make a correction for this. The error is probably not inore than 0-15' C. Measurements were made with silver nitrate solution in order to find whether dissolved gases affect its potential. The results are shown in Table 111. The effects here are very small, only just distinguisliable with certainty. In hydrogen-saturated solution the e.m.f. is 2. or 3 niillivolts lower than in the initial solutions. On blowing carbon dioxide into the solution saturated with hydrogen, thc potential fell about 1.7 millivolts, aiid then rose to 0.5 millivolt above the value for hydrogen. Similar measurements were made with lead acetate and lead nitrate. The electrodes were prepared by coating platinum wires electrolytically as described by Abegg and Labendzinskif and by iiT.K. Lewis.: The values found are given in Table IV. In the case of lead nitrate, next day the P.D. had changed entirely, and Here also the effect of blowing in hydrogen is practically nil, It thus appears that silver acetate is peculiarly sensitive to the presence of dissolved gases. The influence in the case of 0.1 N. AgNO,, 0.5 N. Pb(NO,)* and 0.5 N. Pb(C,H,O,), is almost inappreciable. As the silver nitrate potential is independent of dissolved gases we may compare the values for silver acetate in presence of different gases with this. From the normal depression of the solubility of silver acetate in soiutions having a common ion,$ we may conclude that in solutions of the single salt no complex ions are present. nearly all the lead had dissolved off the electrode (vide Lewis, Zoc.cit.). Taking 0.396 as the mean value for the cell- AglAgNO, 0.1 N/NH,NO, sat./o.I N. cal. electrode at 2 5 O , and setting 0.1 N. cal. electrode = 0.618 volt, we find- Ag/AgNO, 0.1 N. = 1.014 volt. Using the value of Lijb and Nernst for the equivalent conductivity of 0.1 N. AgNO, at 25O, viz., 1093, and Kohlrausch's values for ZAg and ZN03 at * &it. Pltys. Chenz., 17, 1895. t Zcit. Elcktrochcinie, 10, 1904. : Dissert., Breslau, 1908. $ See the next paper.ON ELECTRODE-POTENTIAL 22 I Measurement. I 8*, and their temperature coefficients, we find A, = 133'1, whence y = 0.82 I and 0.059 log = 0.064. This gives E.P. Ag = I - O I ~ + 0.064 = 1'078 volt. Temp. P.1). Time. liemarks. T.4BI.E 111. I 3 25O 0.1 N. AgNO, about three months old.0.4015 0'4007 0'4000 0*4000 0'3995 0'3993 0.3988 0.3970 0.3960 0'3958 0.3958 0.3952 0'3935 0'3942 0'3947 0'3955 0'3959 0'3960 0.3966 0'3963 0'3960 0'3957 0'3955 0'3953 0'3932 0.3923 0'3950 0'3957 0.3962 03960 0'3958 0'3957 Electrode rotated. H, blown through. CO, blown in. Time measured from last measurement. 0, blown in. Rotation stopped. Ag wire electrode introduced. The original electrode again. 0'1 N. AgNO, newly made up with ordinary distilled water. 25.0" 25.0" 25'7" 25.4: 25'1 25.1~ 25'4" 0.3986 0'3976 0'3974 0'3975 0'3958 0'3956 0'3957 0.3956 0 7 niins. 21 ?, 74 9 , H, blown in. Time from last measurement. Apparatus closed. This agrees well with G. N. Lewis' value, for 25', viz., 1'079, although this value was obtained with a special kind of electrode which Lewis found gave higher values than electrodes of the electrolytic kind.322 INFLUENCE OF DISSOLVED GASES hIeasurenient.I P.0. 1 Time. In the saturated silver acetate solution, 0.059 log = 0'0772, so that e + 0.618 + 0'0772 = E.P., where e is the e.ii1.f. of the cell. Putting E.P.= 1'078, as found from the silver nitrate measurements, we find c: = 0.3828. The mean of all the values for the cell with saturated silver acetate in the cases in which hydrogen was blown in, between twelve hours and twenty- four hours after the passage of the gas was begun including the value in Table II., No. 6, and one value not in the Tables)- determinations in all, is 0.3816 volt. Maximum variation = 8-2 millivolts. Mean difference from the value calculated from the silver nitrate measurements= - 1.2 millivolt.The three lowest values for the saturated silver acetate cell were much below the others. In two of thew cases, carbon dioxide had been in the solution Remarks. 33 ,? 19 hours I28 ,, 0'53 75 0.5370 0'5365 0.5362 0'5367 0'5358 0'5359 0.5358 0'5355 O'jO28 0-5014 0'5014 0'5020 O'jooc, App. closed. Lend acefnie, 0.5 K. 86 mins. 1 0 ,1 I20 ,, 176 ,. 0 8 mins. 1 H, blown in. Time from last measurement. H, blown in. Time from last measurement. I previously and in the other P.D. was still rising when the flow of hydrogen was stopped. Excluding thew values, we have for the remaining six, mean = 0.3834. Maximum difference = 3'8 millivolts. Mean difference from silver nitrate value = + 0'6 millivolt. For 0.05 N. silver acetate the concen- tration correction is 0.083 volt, whence, as before- e + 0.618 + 0.083 = E.P.= 1.078. :. e calculated from the silver nitrate value = 0.377 volt. The final values, chosen as in the case of saturated silver acetate, for rill the measurements with O*Oj N. silver acetate in which hydrogen was passed in are 0.3807, 0.3848,0*377~), 0*3826,0*3823. Mean = 0'3817. Maximum variation = 6.0 millivolts. Mean difference from silver nitrate value = + 4'7 millivolts. The values for the saturated solution agree fairly well with one another, and with the value found for 0.1 N. silver nitrate ; those for 0.05 N. AgC,H,O, show a small but distinct difference from this value, and indeed the un-ON ELECTRODE-POTENTIAL 223 corrected potentials agree closely with those for the saturated solution. The agreement with the AgNO, values is a quite empirical result, for there is no n priori reason why the value for the solution containing hydrogen should agree with that for silver nitrate mther than the value for the solution con- taining any other gas.A few measurements were made with silver acetate which had been precipitated from solutions of silver nitrate and sodium acetate, and three times recrystallisecl from hot water. The results were less concordant than those obtained with the salt from Kahlbaum. The results were not concordant. When the solution was saturated with hydrogen the e.m.f. was extraordinarily sensitive to small variations of temperature. In some cases a change of 2O in the temperature of the cell appeared to cause a change of 10 millivolts in the e.m.f. ; the original value could be reproduced by bringing back the temperature to 2 jo. Lowering the temperature lowered the e.ni.f., so that the silver electrode became less positive. Cells were also made up with 0.01 N. silver acetate. CONCLUSIOS. The electrode potential in the system Ag-AgC,H,O, aq. is extremely sensitive .to the presence of dissolved gases in the solution. In 0.05 N. or stronger solutions, definite values of the potential can be obtained in each case by blowing hydrogen, carbon dioxide, oxygen or nitrogen through the solution until saturation is reached. These constant values are different for the different gases. The value for the solutions saturated with hydrogen approximates to the values calculated from the measurements of G. N. Lewis and of Brislee with silver nitrate and Brislee's measurements with silver acetate. In 0'01 N. solution concordant values can hardly be obtained, and the potential in the solution saturated with hydrogen varies very rapidly with small alterations of temperature. Measurements were made with solutions of lead acetate, lead nitrate and silver nitrate, and practically no effect was found due to dissolved gases. This research was begun in the laboratory of Professor Dr. Abegg at Breslau, and completed in Professor Bedson's laboratory at Armstrong College, Newcastle-on-Tyne. I wish to express my best thanks to Professor Abegg for his advice and assistance during the progress of the work, and also to Professors Bedson and Thornton for the kind interest they have shown in it. THE UNIVERSITY, BRESLAU. ARMSTRONG COLLEGE, NEWCASTLE-ON-TYNE.

ISSN:0014-7672    

DOI:10.1039/TF9100500212

出版商:RSC    

年代:1910

数据来源: RSC

摘要:

ON ELECTRODE-POTENTIAL 223 DZSCC'SSZON. Dr. T. M. Lowry said that the abnormal electrode-potentials of silver in contact with silver acetate found a parallel in the electrochemical equiva- lent for silver deposited from this solution, which was abnormally high, rising to 1 0 1 2 mg. per coulomb. The deposit did not consist of pure silver, however, but was backed by a yellowish film of some other material ; pos- sibly, some similar effect was responsible for the curious observations recorded by the author in the case of this salt. Dr. E. Feilmann said it was almost impossible to obtain hydrogen free from zinc if made from that metal. It was therefore quite likely that the224 THE INFLUENCE OF DISSOLVED GASES hydrogen used by the author and blown into the solution contained minute traces of zinc, and this might account for the variations in potential observed. Of course this explanation would not apply to the cases of nitrogen or carbon dioxide. Dr. N. T. M. Wilsmore said that if the effect were due to the pre- sence of zinc, it should take place in the case of the Ag-AgNO, electrode. Besides, if due to the reduction of silver, it would produce an opposite effect to that observed.

ISSN:0014-7672    

DOI:10.1039/TF9100500223

出版商:RSC    

年代:1910

数据来源: RSC

摘要:

CONTRIBUTIONS TO T H E STUDY OF IONISATION IN AQUEOUS SOLUTIONS OF LEAD ACETATE AND CADMIUM ACETATE. By ARTHUR JAQUES, B.Sc., late Fellow of Armstrong College, Newcastle-on-Tyne. ( A Paper read beforc the Favadny Socie fy, Tuesday, November 30, 1909, Mr. JAMES SWINBURNE, F.R.S.? PRESIDENT, in tlzc Chair.) A1 aterials used.-The lend acetate was once recrystallised. AnaEysis.-The lead was precipitated and weighed as sulphate. I. 1.2298 grms. salt gave 0.9823 grm. PbSO,= 54-56 per cent. Pb. 2. 2.0926 grms. salt gave 1.6641 grins. PbSO, = 51'32 per cent. Pb. Theory for Pb(C2H,02),, 3H20 = 54'61 per cent. Pb. The cadmium acetate was obtained from Kahlbaum, and was used as Analysis.- it was. I . 0.4716 grm. salt gave on ignition 0*2280 grm. CdO =48*34 per cent. 2. 0.8986 grm. salt gave on ignition 0'4337 grm.CdO = 48.26 per cent. Theory for Cd(C,H,02), 2H,O = 48.18 per cent. Silver acetate was obtained from Kahlbaum, and was used as it was. The A?zalysis.- salt was perfectly white and crystalline. I . 0.7758 grm. salt gave on ignition 0.5012 grm. Ag = 6460 per cent. 2. 0.6566 grm. salt gave on ignition 0.4235 grm. Ag = 64-50 per cent, Theory for AgC,H,O, = 64-67 per cent. Potassium acetate was obtained from Kahlbaum, and was used as it was. The ratio between the concentrations of the metal-ions in two solutions of The sodium acetate was once recrystallised before use. salts of the same metal can be found by measuring the e.m.f. of the cell- M I MA, xN I MA, yN I M, in which M represents the metal and MA its salt. and C, the respective ionic concentrations, for a divalent metal- If E be the e.m.f.and C, G. Ez50 = 0.0295 log - C , The same result can be found by measuring the two half-elements separately against a standard, e.g., the 0.1 N. calomel electrode. This formula does not include the potential at the liquid contact, which Cumming,:< however, has shown can generally be eliminated by interposing a saturated solution of ammonium nitrate between the two salt solutions. * Trans. Farad. SOC., 2, 213 (1907). 225236 STUDY OF IONISATION IN L4QUEOUS SOLUTIONS The following measurements were all made with cells of the type- M [ MA, xN. I NH,NO, sat. [ 0.1 N. cal. electrode. From measurements of cells of the type- M [ MA,xN, [ 1.0 N.cal. electrode, Abegg and Labendzinski"' found that the metal-ion concentrations in solutions of the acetates of the heavy metals were much smaller than in equally concentrated solutions of the corrcsponding nitrates, and concluded that this was due to extensive complex formation in the single solutions of the acetates.Abegg and Labendzinski's values contain the liquid potentials, and are therefore not quantitatively comparable with the measurements. given in this paper. That complex formation occurs in solutions of lead salts containing excess of an alkali acetate is evident from the fact that lead sulphate is much more soluble in solutions of alkali acetates than in water. It was therefore considered probable that in presence of a large excess of an alkali acetate practically the whole of the lead or cadmium would be pre- sent in the form of a complex ion.If this condition is fulfilled, the con- stitution of the complex can be found by the method of Bodlanderf as follows :- Let the complex have the formula M,Ac, (with Y - 2y negative charges) where M represents Pb or Cd. Applying the law of mass action, we have- whence, if two solutions are considered- First, making [Ac'], = [Ac'] 2, we get- If e be the e.m.f. of the concentration cell containing the two solutions-- whence- Next, making [M,Ac,], = [MqACr].12, we have- and- whence- * Zeif. f. Elektrockemie, 10 (1904). t Fests. 2. Dedckincl, Braunschweig, 1901.OF LEAD ACETATE AND CADMIUM ACETATE a27 Thus, assuming all the metal to be in the form M,Ac,, q and ?’can be A series of measurements of the e.m.f. of the cell found.M I ~~~~’~~ I NH,NO, sat. I 0.1 N. cal. electrode was made. The insulation of the whole of the apparatus was repeatedly tested during the measurements. The electrodes were platinum wires fused through the ends of glass tubes with fusible glass, and were coated electrolytically with lead and cadmium respectively from solutions of the acetates, using very small currents. Both kinds of electrode gave constant potentials immediately on being introduced into the solution, and these were maintained for several hours. Both metals were gradually dissolved by the acetate solutions, so that the potentials did not usually remain constant overnight. All the measureinents were made between 2;” and 25-84 The potentials were reproducible to within I milli- volt. Tables I.and 11. show the results obtained by applying Bodlinder’s method to the values found, putting the complex concentration equal to that of the total lead or cadmium. Putting q = I in Table II., the values of l i n column A are the powers of [Ma*] [Ac’]” Total coilcentration of the salt in solution’ The measuring apparatus was described in the previous paper. 4 [Ac’] in the equation- k = in which k remains constant over the alkali salt-concentration interval between [Ac’], and [Ac‘]~. The values of y for potassium acetate are taken from Kohlrausch’s values for the equivalent conductivity at ISO,:: and his temperature coefficient for the equivalent conductivity of 0.01 N. potassium acetate. The corresponding temperature coefficient for sodium acetate is almost constant over the range of concentration O.OOI-O*~ N.The temperature coefficient of the con- ductivity of potassium acetate is taken as independent of the concentration. A, is found from Kohlrausch’s values for ZK. and ZC,H,O,~ at 18’ and their temperature coefficients. The values for the equivalent conductivity of sodium acetate for concen- tration 0-5-2-0 are from Kohlrausch,::: those for concentrations below 0.5 N. are from 0stwald.f When y from the two sets of values is plotted against vc? a continuous curve is obtained. Arrhenius’ temperature coefficientsf were used, and Am was found as before. The effect of hydrolysis on the conductivity is very small, and has been neglected. The values of q for lead acetate in sodium acetate solutions approximate closely to I, while those for lead acetate in potassium acetate solutions and for cadmium acetate in sodium acetate solutions are a little greater than I.The values of vary rapidly, reaching vcry high values for the strong solutions, and falling to about 2.5 for the acetate ion concentration interval Q * Quoted in Whethain’s Theory of Solution, Table. t Zeif. Phys. Clzeni., vol. i. f From Landolt and Biirnstein, Plt3’sikalisclt-Cltei11ische Tabellen.TABLE 1. . 0'0221 0,0162 0.0074 1'21 1'10 I '20 Conc. NaAc = 1.922. -- Solution 11. Total Pb conc. - - ~ -- 0'003 0*004 0.008 0'01 2 0 '003 0~004 OW08 0'012 Total Cd conc. 0'002 0'004 0.008 Conc. NaAc = 2'792. Conc. NaAc = 0'673. Conc. NaAc = 0.279. Conc. NaAc = 1.153. Solution I. Total Pb COIlC. 0'016 0.016 Total Cd Conc.0.016 - -~ P.D. . - ~ P.D. -- 0.02 j8 0,0184 0.0089 0.0046 -- (1. 1 so4 1'03 1'01 I '12 P.D. ___- 0'0270 0.0163 0.0078 0.0024 P.D. 0.0256 0.0173 0*0088 0'0033 (1. -_ ___ I -03 0.96 I '00 0 -8 q. ~ - - I '02 I '05 0.95 I -05 P.D. 0'0222 0.0170 0~0092 0.00~0 4. 0' 0260 0.01~0 0'0093 0.003 j 0'99 I '09 1-13 1 '54 1'20 I -04 0.97 0.93 Conc. KAc = 0'633. conc. KAc = 1.810. Conc. KAc = 1.086. 0.0215 0.0145 0'0077 0.0033 0'0200 0.0140 0.0065 0*003 1.33 1.26 1'34 I '22 1'24 1'23 1.1; 1'12 o*o163 1 1.10 COllC. NaAC = 2'792. 0.0190 0.014 0~0086 I '03 I -26 I -13 1-17 0'0211 0.0158 0.0076OF LEAD ACETATE AND CADMIUM ACETATE 229 -_ 0'0210 0.0224 0.0240 0.0230 TABLE 11. I ~ 13'4 14.3 15-3 14.6 -- P.D. 0'0212 0.0234 0'0220 0.0230 0.0232 0.0151 0.0170 0.0152 0.0167 0.0156 0.0373 0.0395 0.0412 0.0404 0.0409 A.r Q -. 2'34 2-54 2 -58 2 *56 2'43 3 '2 3'6 3'2 3'5 3'3 B. rcalculated from bquation(Ig)(q= I). 2 '91 3 '59 3 '57 3-62 3'09 Mean = 3 -36 3-96 4-46 3 '91 4 '34 4-06 9'91 10.32 10.79 1052 10.71 Total Conc. of Pb in both Solutions. 0'002 0.004 0.008 0.016 0 012 0'002 0.004 0.008 0.016 0'012 0'002 0.004 0.008 0.016 0'012 [Ac'l 1. (NaAc 0'279 N.) 0.179 (NaAc 0.673 N.) 0.363 [Ac'l2' (NaAc 0.673 N.) 0'363 ~~ (NaAc 0.526 1.153 N.) (NaAc 2'792 N.) 0.729 8.9 9'45 9 '9 9'7 9 -8 (NaAc 0.526 1.153 N.) 18 23 23 22 22 0'002 0'004 0.008 0.016 0'012 0.0154 0.0185 0*0190 0.0188 0.0193 0'0205 0.0195 0'0193 0.0203 0.0190 0.0272 -___ 0.03 jo (NaAc 1-922 N.) 0.682 ( KAc 0.633 N.) 0'438 (KAc 1.086 N.) 0.67 P (NaAc 0.279 N.) 0.179 (NaAc 2'792 N.) 0.729 (KAc 1.086 N.) 0.67 I ( KAc 1.810 N.) 0.952 6.92 5 '22 5.10 4'46 4-26 3 '73 3 5 6 3'7 3'5 3'5 0'002 0.004 0.008 0.016 0'012 0.004 0.016 Total Conc.of Cd in both Solutions. 0'002 0.004 0.008 0.016 3 % 3 '2 2 '9 3'1 Mean = 3 '25 0.0270 0.0276 0.0265 0.0275 0'02 I 0 0.02 I 6 0.0225 0 '0220 (NaAc 0'837 N.) 0.425 0'002 0.004 0.008 0.016 (NaAc 1.674 N.) 0.645 (NaAc 0'837 N.) 0.425 (NaAc 0.64 j 1 -664) 5'1 5 '3 (NaAc 2'792) 0.729 0'002 0.004 0.008 0.016 15.1 16.1 The absolute potentials against the 0'1 N.E. are given in Tables X. and XI v.230 STUDY OF IONISATION IN AQUEOUS SOLUTIONS o.I&ca 0.4. If q may be taken as really I, it follows that at this acetate concentration a considerable part of each salt must be in the simple undis- sociated state, as PbAc, and CdAc,, or as PbAc' and CdAc'.Since the acetate concentration in these mixed solutions is certainly much greater than in, say, 0.05 N. single solutions of lead and cadmium acetates, it seemed probable that ionisation in these solutions leads chiefly to the formation of PbAc. and CdAc.. It was therefore thought worth while to see whether constant values for the dissociation constants would be obtained on the assumption that ionisation occurs in the single solutions according to the scheme- MAC, * MAC. + Ac', MAC. Q M.. + Ac'. A similar case has been worked out by W. K. Lewis ::: for lead nitrate. Following Lewis's method for the calculation of the constant for the second dissociation, we have, for lead acetate-. . . . . . . . . . (3) LAC'] = I(, [ P b Ac,] - . .. . . . (4) . . . . . . c=[Pb..] +[PbAc.] +',PbAc,] (5) where c = total lead concentration. Further, since the solution is electrostatically neutrd- . . . . . . . (6) 2 [Pb-] + [PbAc.] = [Ac'] From (4) and (6) by elimination of [PbAc-] we get- z[Pb-] K, K2-[ P b**] [Ad] = From (5) and (6)- [PbAc,] = c - [Ad] + [Pb..] . . . . . . . CPbAc.3 = [Ac'] - 2[Pb**] (7) From (3) and (4), and substituting for [PbAciI- Substituting for [Act]- c-lc, which reduces to Lewis's equation, viz- K: (c - rPb-1) - K, (c + -- 2[Pb.*] + [Pb.*]"(c + [Pb**]) = o . (8) "["1*) * Dissctd., Breslau, 1908.OF LEAD ACETATE AND CADMIUM ACETATE 231 4Pb-I: - is sufficiently small to be neglected in comparison with c, we KI If obtain- . . . (9) Substituting froin equation (7) in (3) and (4) we obtain- The value of [Ac'] in the single solutions can be roughly estimated from the depression of the freezing-point.Adding together the concentrations of all the molecules in solution we get, making the same assumption as in equation (5)- [Pb*.J + [PbAc.] + [PbAc,] + [Ac'] = ic . . . . (12) Subtracting (5) from this- [Ac'] = c(i - I ) . . . . . . . . . (13) A series of potential measurements in single solutioiis of lead and cadmium acetates was made. The values found are given in Table 111. The poten- tials in the single solutions were not quite so constant as those in the mixed ones, possibly owing to the higher resistance. They showed a maximum variation of about 2 millivolts, excepting in the case of 0.01 N. PbAc,, where the maximum variation amounted to about j millivolts. TABLE 111.C. 1P.D. against 0.1 N. cal. electrode. O ' j 0'1 0'0 I 0'536 05380 0.5368 0.5390 0'54T 0.7892 ::gg 0'8037 In the lead acetate cells the variation in the potential with change of concentration is remarkably small. This indicates that there is little change in the concentration of the lead ions even on diluting the 0.5 N. solution up to fifty times its original volume. This indicates that the value of K, is small, and the behaviour is similar to that found by Luther:: in the case of sulphuric acid, where the potential of a mercurous sulphate electrode only changed 3 millivolts over the range of concentration I*O-O'I N. * Zcit. f. Elcktrocltcniic, 1907, 294.232 STUDY OF IONISATION IN AQUEOUS SOLUTIONS In the cadmium acetate solutions the change is more rapid, and indicates In order to find the order of magnitude of K,, the freezing-points of thc ) for various Table IV.shows the values of i =- a higher value for K,. solutions in Table 111. were determined, or obtained by interpolation. ( molecule depression 1.85 solutions of the two salts. TABLE IV. Grm. Mol. 1,000 grams H,O Lead Acetate ... Litre Cadmium Acetate... .! to" I to's Freezing-point. - 0.13 - 0'34 - 0.54 - 0'20 - 0'31 - 1-16 -0.39 - 1'597 .__- i. -~ 2.32 1-78 1-51 1.189 1 *% I 26 1.726 2'1 I ~ [ i - I] = [Ac']. 0.0398 0-047 I 0.06 I 8 0'0455 0.069 0'13 0'111 0.363 For the present purpose, the gram molecule per 1,000 grams of water was taken as equal to the grain molecule per litre. Plotting c against c(i-r), the first three of Kahlenberg's values give a straight line, c(i -I) increasing with the concentration, while the fourth shows a sudden drop in i and c(i -I).The freezing-points of 0-1 and 0.5 N. solutions were determined, and the values found are shown in the table. Kahlenberg's fourth value was neglected. Table V. shows the values of K, and I(, obtained by inserting the experi- mental values in equations (13), (10) and (11). The values of [Pb-] are calculated from Lewis's value for the E.P. of Pb, viz., - 0'403 volt against the 1.0 N. cal. electrode at 25'. Taking the 0.1 N. cal. electrode as being 0'054 volt positive to this, we have E.P. of Pb against 0.1 N. cal. electrode For cadmium, the value quoted by Le Blanc,: viz., - 0.703 against the =- 0.457 Volt. 1.0 N. cal. electrode was used.TABLE V. 0.5 0.05 0'1 0'02 0'0 I 0.5 0'1 0'002 I 0 o*oo I 80 0*00197 0-00166 0'00142 [Cd-] 0.08 I 0.0566 Y 0'04.4 0.138 0.265 - - 0.335 l - 0'002 I7 0.0019 om02 16 0.0018 0'001 55 0'146 -- * Kahlenherg, Zeit. Pltys. Client., 17, 1895. t My observation. 1 I Interpolated from Kaldenberg. Lelzrbzich dcv Elektroclienzie, 4th edition, 1906.OF LEAD ACETATE AND CADMIUM ACETATE 233 From equations (10) and (11), it is seen that the values of K, and K, become unreliable when [Ac'] - 2 [r\lr**]= o or [Ac'] - (c + [M**]) = 0. In the 0.5 N. solutions these differences are relatively large, so that the values of K, and K, may be taken as indicating roughly the order of magnitude of the two constants. From Table V., therefore, it appears that for both salts 2[n/r'*1z ~ is small enough to be neglected in comparison with c.I t will now be convenient to consider the lead and the cadmium separately. K, A LEAD ACETATE. KI From equation (S), neglecting 'm, we may either (I) assume K, to be constant and calculate K, and [Pb-] by trial, using the relation- [Pb-] e = 0'0299log -- - f [Pb-I,' or (2) using the known E.P. of lead, calculate K,. I . From the P.D. measurements- whence- Inserting values for [Pb**] in accordance with this relation, we find that K2(0.5) = K2c0.01) when [Pb*.] (o'oI) = 0.00187 and K, = 000272. 2. Using Lewis's value for the E.P. of lead, we obtain the results given in Table VI. TABLE VI. C. 0.5 0.05 0'1 0'02 0'0 I - [Pb-J. 0'002 I 0 0'00 I80 0-00197 0.00166 0'00142 - K,. 0'002 I 0.00187 0-002 13 0wo I 89 0'0020 Mean =0~0020 K,, Corrected.0*002 I 8 0.00196 om0228 0*00203 0'002 I 0 0'002 1 The two values agree within the known limits of variation of the potentials. Putting K, = 0*0020 in equation (9) and solving for [Pb-] , we find- [Pb..] o'j = 0~00198, [Pb**],.,, = 0.0015, whence e = 0.0036, which is a sufficiently close approximation to the experi- mental value. The value 0*0020 may be taken as an approximation to K,. All these calculations contain the small error due to neglecting the term containing K, in equation (8). In order to find K,, the solubility of silver acetate was determined in solutions of sodium acetate, potassium acetate, silver nitrate, and lead acetate. This affords a quantitative means of determining the acetate ion concentra- tion in the mixed solution.Knowing this, we can calculate K,.234 STUDY OF IONISATION IN AQUEOUS SOLUTIONS 1'0 0'1 0 5 0.05 0'01 The values found are given in Tables VII. and VIII. The silver was precipitated and weighed as iodide. In the case of lead acetate the separation was effected by the method of Benedict and Gaus.*: Parallel analyses were made throughout. In solutions of the alkali salts and of silver nitrate the method gave concordant results withotlt difficulty, in the lead acetate solutions small differences between the two analyses were found. Whenever these approached I per cent. two new determinations were made with a fresh lot of solution. The solutions were shaken for at least 24 hours in the thermostat at 25'. They all darkened somewhat during shaking, excepting the silver nitrate solutions.For the lead acetate only the mean values are given, as these were taken in some cases from three or four values, the maximum difference never exceeding I per cent:t 0.03587 0'04349 0'01995 0.0566 0.06403 TABLE VII. Conc. (u) KC,H,O, = c. 2.262 1.131 0.2262 0.0226 2'403 0.2403 0*0240 (c) AgNO,. 0.1307 0.06535 0.03268 0'01634 (6) NaC,H,O,. 1'201 I. 0*01305 0'0 I 440 0.02654 0.05743 0.0 I 240 0.0 I 402 0.025 I 4 0.0349 0'0443 0.054 I 0'0594 0'05552 y for the added Salt. 11. 0.0 I 305 0.01443 0.02652 0.01238 0.01390 0.02 5 23 0.0346 0'0445 0.0539 0.0596 0.05758 0'05562 Mean. 0'01305 0'01442 0'02653 0'05750 0'01 239 0.01 396 0.025 19 0'05557 0.0348 0'044.1 0 ~ 5 4 0 0'0595 0~01os) 0'0209 0.0300 0.0572 0'0218 0.03 I 5 0'0579 0.03 69 o*o&o 0.0541 0'05945 0'02 I The fact that in the strong solutions of potassium and sodium acetates the calculated solubility is greater than the value found indicates that is lower than the true value of 7.A, TABLE VIII. Solirbiliiy of Silver Acetn ie in Lend Accinie Solziiioiis. C. I). 0.01 867 0.0263 I 0'03275 0.0394 0.0468 0' I297 0'092 I 0'0739 00614 0.05 I7 I 1 * Crookes, Selcct Methods, p. 324. t See remarks, Landolt and Bornstein, p. 518.OF LEAD ACETATE A4ND CADMIUhI ACETATE 235 Conc. o.oS64 (sat .) 0.05 Two independent determinations of the solubility in water gave the values The results for the alkali acetates and silver nitrate show that Its conductivity was measured at 0*0662,0*0665. silver acetate is a perfectly normal salt. 2jo, and the results are given below :- I I1 11 * Ye A.Y. 75'2 0.74 I 74.76 0'737 78.6 0'771 - - The values for the saturated solution show fair agreement with that found by Rudolplii ;:: (74'45). The first values were used in making the calculations. For A, Loeb and Nernst's value, 101.5, was taken. In the saturated solution [Ag.] = yti = 0'0492, and the solubility product [Ag.] [Ac'] = (yq)2 = 0'00242, and the concentration of the undissociated part which remains constant in all saturated solutions = 0.0664 - 0.0492 = 0,0172. The calculated solubilities given in Table VII. were obtained using the formula- We shall call this concentration A. in which x is the concentration of the common ion .in the added electrolyte, s is the solubility of silver acetate in water.In the mixed solution, in addition to equations (3), (4), and (s), adding together the acetate concentrations, we have- We are now in a position to calculate K, for lead acetate. q + 2~ = [AgAc] + [PbA4c*] + 2 [PbAc,] + [Ac'] . . . (14) [Ag-] + [PbAc.] + 2 rPb**] = [Ac'] . . . . * (15) and for electrostatic neutrality- From (4) and (15)- [Ac'] - [Ag] = [PbAc.] (I + s), 1.e.- . . . . . . . (16) Also- * Zcit. Phvs. Ckem., 17, 1895.236 STUDY OF IONISATION IN AQUEOUS SOLUTIONS [Pb-] 0.00167 0'001 37 0~00106 0*00068 0-000 I 7 From (14)- KI 0'0157 0.0133 0.0482 O'O* 0.044 I Mean = 0.033 From the values of [Ac'] in Table VIII. and equations (16) and (IS), and using the approximate value of K, already found, we can calculate K,. Since in equation (16), 2K, is always small compared with I, the error in K, can only produce a niuch smaller one in the value of K,.[Ac 1 [Ad] 0- I 297 0.0921 0.0739 0.0614 0.05 I 7 TABLE IS. (K, is calculated, also [Pb-] for comparison with the values given in Table VI.) [PbAc.] [PbAcz] -.- 0.1077 0.8906 0.0630 0.4356 0.0391 0.0599 0*0207 0'0286 o*oo+52 0*00530 Lend Acetate Solution saturated with Silver Acetate. C. 1'0 0'1 0'01 0'5 0.05 K, appears to vary over the range of concentration C = 1.0 to C = 0.1, but, for the purpose of making the small correction in equation (8) the mean value 0'033 was used. The corrzction is very small. The corrected values are given in Table VI. Solviiig equation (8) by trial without approximation, we find [ Pb*.],.,, = 0*00164, K2(o.5--oo,) = 0*00247. These values agree closely with those calcu- lated using Lewis's value for the E.P.of lead. Since Lewis's value rests upon a niuch bigger potential difference, the results given in Table VI. are probably the more accurate. From the fact that in relatively strong alkali acetate solution only amounts to 2.5, !l that K, calculated from the solubility of silver acetate is nearly constant, and of the same order of magnitude as the values calculated from the freezing- point determinations, and that K, Calculated from Lewis's value for the E.P. of lead is also constant and i n agrcciiieiit with the values found without assuming any value for the E.P., it appeared reasonable to conclude that the assumption that ioiiisation in the single solutions occurs normally according to the scheme- We thus find KZ = 0-0021, K, = 0.033.PbAc, = PbAc. + Ac' PbAc. = Pb.* + Ac' was justified. The real total concentration of the complexes in the mixed solutions can now be calculated. Calling this C, and the total lead concentration c, we have C = c - [Pb-] - [PbAc.] - [PbAc,]. Table X. shows the values of C in the solutions used in Table 11. Since for constant Ac' - concentration C is nearly proportional to c, the values of qOF LEAD ACETATE AND CADMIUM ACETATE 237 calculated from equation (I) on the assumption that all the lead was present as complex are practically unaffected. TABLE X. K, =0'033 ; K,=0~0021. '.D. against 0 1 X.E. [Pb"] C. 0.6232 0.612 j 0*6040 0.5985 0.5962 2*32*10-~ j.36' 10 - 1.60- I0 - 5 I -91 * I 0 - 5 I '04'10-5 0'000709 0'002212 0-001 0 I 7 0.003093 0.00; 3 6 8 1.87'10- 5 3'0 1.I 0 - 5 2'70' 10-5 2'97'10-5 2'04.10-5 Mean = 2'5'10-5 0'179 (NaAc) 0'002 0.004 0.008 0.016 0'012 0~00106 j 0-002127 0.004442 0.006 j47 0.0086 j 0'363 (NaAc) 0.6444 0.6355 0'6273 0.62 I 8 0.6 I 80 0.6594 O'Bj2 0.642 5 0.6382 0.6336 0'002 0.004 0.008 0.0 I 6 0'012 0.526 (NaAc) 0-00 I 406 0.00294; 0.00 578 0.008gO 0'01 1 56 0'002 0.004 0.008 0.016 0'0 I2 1 0.6967 0.69 I 5 0.6837 0.678 j 0'6745 7'50'10-9 I - 12' 1 0 - 8 2.07. I 0-* 3*10*10-* 4-21' I O - ~ 0'729 (NaAc) - 0.438 ( KAc) 0'002 0.004 0.008 0016 0'0 I2 - 0'002 o.ooL+ 0.008 0.016 0'0 I2 0.001939 0'003909 0.007832 0'0156j 0'01175 (O'oO03 2) 0~001~1 0.003 I 7 0.00 j90 0.00860 0.64 I ;* 0.63_53 0.6280 0.625 0.6225 5'j7'10-7 8-89. IO-' I .60.10- 2'02'10--s 2.4 j*10-~ 0.6620 06550 0.6482 0.6438 0.6410 0'002 0.004 0.008 0.0 I 6 0'0 I2 I * I ~ * I O - 7 I '94' I 0-7 3 '30' I 0 - 5*80*10-7 4'66.10- 7 0'00 I2 25 0.0026 j 8 0-00 j72 0.00878 0'0120 1 0-6822 0.6662 0'004 0.016 0*00370 0.0 2489 Assuming the concentration C to be that of a single complex, we can now calculate its constitution.As before-238 STUDY OF IoNIsxrIoN IN AQUEOUS SOLUTIONS Should the alkali metal enter into the complex as found by Lewis in the case of lead nitrate and potassium nitrate, let the complex have the constitution K9P bqA&. Then- Le., Y in the above equation would become p + r. Therefore- and- qe + 0.029 j log 2 - c, [AC’], . . . 0 6 . . . * * (19) - 0.0295 log - The corrected values of r calculated in this way, putting q = I, are given The effect of the correction is to raise all the values Taking 7 = 3 in 0.279 N.sodium acetate solution, which is also weak in Table II., column B. considerably. enough to be treated as “dilute,” we can now calcdate- [Pb**] [Ac’] 3. Ks= [PbAc,’] The values are given in Table X. The mean value is 2-5.10-5. It is now possible to test further the hypothesis made in calculating K, and K2, namely, that complex formation in single solutions within the concentration interval o*o~-o*~N. is of negligible degree. We now have- [ PI>**] [XC’] 3 K3 [PbAc‘,] = and- We thus obtain the following values for the concentration [PbAc;]- PbAc,. 0.126 0 1 000115OF LEAD ACETATE AND CADMIUM ACETATE 239 The hypothesis is therefore not quite true. The values of [PbAc,] cannot be taken as correct, since they are calculated on the assumption that [PbAc,'] =o.The error in K,, however, must be roughly proportional to [PbAc,'] in the above table, and must therefore be much less in OOI N. than in 0.5 N. solution. Since in Table VI. the values calculated for the different concentrations using Lewis's value for the E.P. of Pb are very nearly constant, it is evident that the error must be very small. This is further shown by the investigation of cadmium acetate. The error in I<, cannot be determined with certainty. From equations (4), (14), and (IS) we find that allowing for the formation of a complex anion of the type PbAc, in the solutions saturated with silver acetate would have the effect of raising K,. The value of K, found from the freezing-point of the single solutions is independent of complexes, since the term representing the concentration of the lead as complex in equations ( 5 ) and (12) disappears on subtraction.It seems safe to conclude that K, cannot be less than 0.04. Raising the value of K, has the effect of raising C and lowering the value of log 5 i.e., lowering the value of I-. As r cannot be less than 3, it appears from Table 11. that in dilute alkali acetate solutions the complex PbAc,' is formed in larger quantity than any other. Taking C = [PbAcJ and giving K, the limiting value 0.04, we find for K, in the same order as in Table X., 1*45,2'06, 1*90,2*03, 1'55 x 10-5. Mean value = 1*8010-5. Since raising K, lowers K,, it follows that K, cannot be greater . than 1*8*10-5= roughly 10-5.Three circumstances may possibly account for the extraordinarily rapid decrease in the ,lead ion concentration with increasing Ac'-concentration in the stronger alkali acetate solutions, namely : (I) departure from the laws of dilute solutions, including error in the values of y ; (2) the formation of one or more complex ions containing a large number of acetate groups in the ion ; (3) the formation of undissociated salts between the alkali metal ion and the complex ion. That the values of y are inaccurate appears certain from the values for the solubility of silver acetate. The presence of the alkali metal in the complex ion appears unlikely for the following reasons :- (I) Only one case has been found as yet where this occurs. This is in the ion KPbNO;' which Lewis:: found in solutions of lead and potassium nitrates. (2) While in the foregoing case the conditions in solutions of sodium nitrate and potassium nitrate were totally different, sodium nitrate giving no indication of complex formation, in the present case the behaviour of the two alkali acetates is very similar.c,' B. CADMIUM ACETATE. In this case the potential differences in the single solutions of concentra- tion O*S-O.OI N. were much greater than for lead acetate, and K, and the Cd--concentrations were calculated-without assuming a value for the E.P. From equation (S), neglecting 2[Cd"12 and [Cd**]3, we find- K* * LOC. cit.240 STUDY OF IONISATION IN AQUEOUS SOLUTIONS 0.6483 0-01205 0.00318 0.2486 0.0294 It was found that the only admissible values of I<, were obtained by taking the negative roots in this equation, and these agreed with the positive root of equation (S), when the same terms were neglected.Solving equation (20) with the value of e obtained with cadiniuni acetate (given in Table III.), we find K,= 0.0207. The solubility of silver acetate in solutions of cadmium acetate :it 25" is given in Table XI. 0.0183 0'0080 0.0019 0.0174 0'01 I 6 TABLE XI. Solubility of Silver Acetate iit Cadmitiin Acetate Solution at 25'. C. 1'0 0'1 0'0 I 0'5 0'05 ,I 0.02363 0*02592 0'0402 I 0.04852 0.06224 1 ) - ;\ = r.4g.1. 0.00043 0.00872 0*02301 0'03132 0.04504 L - [Ag'] - 0'37% 0.2776 0.1052 0.07729 0'05375 'l'ahle XII. shows the values of K, found, using K,=0-0207. Solving cquation (S), without approximation, using K, = 0.188, we find [Cd*.] o.5 = 0-0170, and K, = 0.0198.TABLE XII. C I '0 0'1 0'0 I 0.5 0.05 [Ac'] . 0'3765 0.2776 0.1052 0'07729 0.05375 [CdAc] . 0'3334 0'2340 0'0590 0.02994 0.00492 I I<, . 0'194 0.261 0.192 0.083 Mean = 0.188 0'21 I K, and [Cd-] were now calculated for the other concentrations, using the potential measurements, and the relation- The results are given in Table XIII. TABLE XIII. c. 0.5 0'1 0'02 0.01 [Cd-J. 0.0 I 70 0.01 19 0.00698 0.0054 8 0.0198 0.0161 0.0155 0.0198 Mean = 0.0178OF LEAD ACETATE AND CADMIUhf ACETATE 241 CdAc,. The values of [Cd-] give the E.P. of Cd = - 0.737 against the 0.1 N. cal. electrode at 25". This gives - 0.683 against the 1.0 N. cal. electrode at 25'. In order to find the probable error in this value, equation (8) was solved, allowing an error of 3 millivolts in the potential measurements between 0.j and 0.01 N.solutions. = 0.01 15 instead of 0.0145, we find [Cd..],., = o*o108 and K, =0~0119. This gives the E.P. - 0.7312 against the 0.1 N. cal. electrode. The error chosen was greater than the probable error. From these mea- surements the E.P. of cadmium is therefore - 0.737 & 0.006 volt against 0'1 N. cal. electrode at 25O, or - 0.683 & 0-006 volt, against the 1.0 N. cal. electrode. As in the case of lead, the complex concentration C was calculated for the solutions given in Table 11. The values are given in Table XIV., and the corrected values of r in Table 11. Putting eWj - TABLE XIV. (K, =0.188 ; K, = 0.018. E.P. of Cd against 0.1 N.E.= -0.737 volt.) [CdAcjJ. 0.645 0'729 C. 0'002 0*004 0.008 0.016 0.002 0.004 0.008 0.016 0'002 0'004 0.008 0'016 0.002 0.004 0.008 0.016 P.D. 0'857 O%jI 0.843 0.834 0.8840 0,8786 0.8695 0.8615 0.9055 0.8995 0.8915 0.8842 0.9265 0.922 0.916 0 7 [Cd-1. 8-gj.10-5 2-55'10-4 I '37'10'4 3'15'10-4 r '04' 10 - 5 3'23'10-5 6-02' 10-5 I '59' 10-5 I -94- 10 - 3.10.10-~ 1*02'10 - 5 3'79' 10' 3-77' 10-7 5*36*10-7 8.56*10-7 1'73'10'6 C. 0*0002548 0wo I 204 0.002795 0-005488 0-oOO860 0.0022 j7 0'004459 0.009400 0*001925 0.0 I 566 0.003894 OW07830 As before, K3 was calculated from the data for 0'279 N. sodium acetate solution, putting r = 3, and the values are given in Table XIV. The mean value, excluding the first one, is 5'7'10-4. Calculating the values of [CdAc,'] from this we obtaiii- c.0.5 0'1 0'0 I 0'414 0.0158 0.-335242 STUDY OF IONISATION IN AQUEOUS SOLUTIONS The error is thus much greater than for lead acetate. We shall probably remove nearly the whole of the error in K, by calculating it for the concen- tration-interval c = O*I--O*OI instead of c = 0'5-0.01. Kz,o.r4.0r, = 0~0097 = roughly, 0.01 & 0*002, [Cd.*],., = 0.0082, Doing this, we get- so that the values are reduced by about half. From the freezing-point of 0.5 N. cadmium acetate, and the solubility measurements, we may conclude that K, cannot be less than 0.2. Further, putting K, = 0.01, when K, falls below 0.3, C becomes small or negative for the three best data in Table XIV. for [Ac'] =0*179. Taking E.P. of Cd = - 0.732, however (see below), we get for the limiting value 0.13.K,, therefore, cannot be less than 0.13, and is probably greater than 0.2. The new value for the E.P. gives lower values for K,. K,, therefore, cannot be greater than 5'10-4. It follows, as in the case of lead acetate, that in dilute sodium acetate solution the complex CdAcj is formed in larger quantity than other complexes. 0.006 volt against the 0.1 N. cal. electrode or - 0.678 + om06 volt against the 1.0 N. cal. electrode. The correction in K, thus makes a change of 5 millivolts. It is probable that the reniaining error in this value due to complex formation in 0'1 N. cadmium acetate solution is of negligible magnitude. The limits of error for this value of the E.P. are rather wide apart, but it is given because it differs by much more than the probable error from the value accepted at present.The removal of the error due to the presence of a complex in the stronger solutions increases this difference. From the value [Cd**],., = 0.0082 we find the E.P. of Cd = - 0.732 SUM MARY. From measurements of the e.m.f. of cells of the types- p b I ;:$! I NH,NO, sat. I 0'1 N. cal. electrode, Cd 1 g:z;;{ 1 NH,NO, sat. I 0.1 N. cal. electrode, it was concluded that complex formation in sirigle solutions of lead acetate and cadmium acetate was small, and that the complex concentrations might be small enough to be neglected in calculating the two pairs of dissociation constants for the respective salts. From measurement of the e.m.f. of the cells- Pb I PbAc, xN I NH,NO, sat. I 0.1 N. cal. electrode, Cd 1 CdAc,, xN I NH,NO, sat. I 0.1 N. cal. electrode, the value 0'0021 was found for &, the second dissociation constant of lead acetate, and this value shows good constancy over the range of concentration 0-5-0*01 N. ; and it is probable that the value of I<, is greater than 0'04. On the assumption that sodium and potassium do not form complex ions with lead acetate or cadmiuiii acetate, evidence was given to show that in dilute alkali acetate solutions complex formation in the case of lead acetate leads chiefly to the production of the ion PbAci. K,, the dissociation constant for this complex, cannot be greater than 10-5. The small second dissociation of lead acetate is comparable with that found by Luther" for sulphuric acid. * I m . cif.OF LEAD ACETATE AND CADMIUM ACETATE 243 The most probable value for K, for cadmium acetate is 0'01 $-0*002, and K, is probably not less than 0.2. In dilute alkali acetate solutions the com- plex CdAcl is formed in larger quantities than other complexes. Its dissocia- tion constant, K3, cannot be greater than 5 x 10-4. The values of r, the number of acetate groups in the complex, rise very rapidly for both salts with increasing alkali acetate concentration. The E.P. of cadmium was calculated to be - 0'732 &coo6 volt against the 0'1 N. cal. electrode, or - 0.678 t_ 0.006 volt against the 0'1 N. cal. electrode, at q0. In conclusion, I wish to express my best thanks to Professor Dr. R. Abegg for kind assistance in the conduct of this research, and also to Professors Bedson and Thornton for the kind interest they have shown. ARMSTRONG COLLEGE, NE\~c~~sTI,E-o~-TY~E.

ISSN:0014-7672    

DOI:10.1039/TF9100500225

出版商:RSC    

年代:1910

数据来源: RSC

摘要:

OF LEAD ACETATE AND CADMIUM ACETATE 243 DISC USSIO” Professor R. Abegg (comintenicnlcd) : As the knowledge of the consti- tution of salt-solutions is far less than is generally assumed, it is a matter of greatest importance for the theory of ions to settle the question for as many salts as are amenable to our present methods. Mr. Jaques’ measurements bring us a great step forward, showing how complicated the ions of his two salts are, being far from the simple cations and anions which seem to compose them. The applicability of the mass law for ionisation problems has seemed hopeless in spite of many trials. I am sure that researches like Mr. Jaques’ will restore the validity of the mass-law even for “strong electrolytes,” and this prospect renders this research valuable, and worthy of continuation in the case of other salts.

ISSN:0014-7672    

DOI:10.1039/TF9100500243

出版商:RSC    

年代:1910

数据来源: RSC

摘要:

THE CALORIMETRICAL ANALYSIS OF HYDRATED SALTS. BY F. G. DONNAN, PH.D., ASL) G. D. HOPE, PH.D. I. INTRODUCTIOS. Thonwxi, in his ~lzerntocl~entiscl~e U/tfersuclzurtge~t (vol. iii.), describes a long series of accurate investigations on the heats of solution of hydrated and partially dehydrated salts. His object in carrying out these measurements was the determination of the constitution of salt hydrates. The method con- sisted in subtracting from each other the values found for various states of hydration of the ‘‘ salt ” under investigation, and so endeavouring to find the total energy change per successive addition of one gram-molecule of water to the solid salt. It is unprofitable at the present time to enter into any detailed analysis of the methods pursued by Thomseii in the interpretation of his experimental results.It must suffice to say that, partly owing to a want of that light which OUT present-day knowledge of heterogeneous equilibrium gives us, and partly for other reasons, Thomsen’s conclusioiis are in many cases quite erroneous, whilst in other cases his results do not lead him to any definite conclusion. Two examples will be sufficient to support this state- ment. In the case of sodium carbonate Thomsen deduces from his calori- metric data the existence of hydrated salts containing, respectively, I, 2, 5, 7, 8, and 10 molecules of water per molecule anhydrous salt.::: It will be shown in this paper that when Thoinsen’s results are correctly interpreted they indicate quite clearly and definitely the existence of only three hydrated salts, namely, those with I, 7, and 10 molecules water per molecule anhydrous salt.And that these are the only stable hydrates which exist has been proved by the careful work of Wells and McAdam, jun. (Jozcrrt. Amer. Clzetrz. Soc., 1907, Again, in the case of the sulphates of the “vitriol” series, e.g., ZnSO,, 7H,O, &c., Thomsen does not appear to arrive at any acceptable conclusions. It will be shown in the sequel that in the particular case of copper sulphate Thoinsen’s experimental results indicate with certainty only the existence of the penta- and mono-hydrates. In obtaining his partially dehydrated salts, Thomsen caused the finely powdered highest hydrate to slowly dehydrate in a current of dry air at a relatively low temperature. As a method of successive dehydration this pro- cedure is open to considerable objection, because, owing to the absence of equilibrium conditions, the question of the relative velocities of dehydration of the successive possible hydrates arises.We do not know, therefore, whether at any moment we have to deal only with two hydrates, i.e., two * In the subsequent abbreviated edition of his researches (S)sfcmtrfisclzc Durcli- fii1wtm:l Thermocheiitischer Illcsstiitgcri, Stuttgart, 1906) Thoinsen speaks much moKe guardedly concerning his results with sodium carbonate, but the interpretation IS equally unsatisfactory. 244 29, 7 4 .T H E CALORIMETRICAL ANALYSIS 345 solid phases, as woulcl be the case if equilibrium obtained, or whether there may not be present siinultancously three or more solid phases.Should the latter alternative happen to be the true one, it is clear that no definite inter- pretation of the calorimetric data is possible. The only theoretically sound method would be to agitate the given partially dehydrated and finely powdered salt mixture in an enclosed evacuated pulveriser until equilibrium had been obtained. It may be conceded, however, that Thomsen’s procedure may approximate very closely to equilibrium conditions (Le., successive dehydration and + 6000 + 3000 0 : u $ -12000 - 15000 I8000 0 1 2 3 4 5 6 7 8 9 1 0 x = Mols. H20 per No/. Anhydrous Salt @a2 CUJ FIG. I.-Hydrates of Na,CO, (Thomsen). presence of only two solid phases) when the process of dehydration is sufficiently slow and the salt mixture continually -repulverised. Granting then that under favourable conditions we have to deal in any given mixture with two successive hydrates, we may proceed as follows.Taking the case of sodium carbonate for example, and denoting the average composition by the formula Na,CO, . xH,O, we have- Na&O,. .rH,O =P(N%,CO,. mH,O) + q (Na,CO,. rtH,O),246 THE CALORIMETRICAL ANALYSIS where ~ l t and $2 denote the mols. water present per mol. Na,CO, in the two co-existent hydrates. From the above equation we get p = - - - - 111 - I I J q = m z r z ' where m > x > n. x - 11 m - x Let the heats of solution (in dilute solution) of the hydrates in and n bc -+ 6000 + 3000 0 P -3000 $ y -9000 0, Q m .Q t -12000 e G -15000 - I8000 0 I 2 3 4 5 6 7 8 9 I0 x = Mds. H20 per Mol.Anhydrous n/a,C& FIG. 2.-Hydrates of Na,CO, (Donnan and Hope). a and b calories respectively per gram formula weight. Then the heat of solution y of the mixture Na$O,. xH,O per gram formula weight will be given by the equation- x--12 m - x Y = a m--n 4- b mnn' Thus if we plot y as a function of x each pair of successive hydrates will determine a particular straight line, so that the result will be a series of straight lines intersecting at the values of x corresponding to the successive definite hydrates.OF HYDRATED SALTS 217 It may be here remarked that, apart from the other factors discussed above, the validity of this method of procedure depends on the assumption that the heat of solution of a mechanical misture of two definite hydrates is equal to the sum of the heats of solution of the same quantities of the two hydrates determined separately.This assumption will doubtless hold good with sufficient approximation provided the heats of solution in sufficiently dilute solution are measured. Should any of the successive hydrates form niolecularly homogeneous mixtures giving monophase systems, the y = $ (x) linear complex will transform partially or completely into a continuous curve. It is probable, however, that this case is not very common. 2. ESPERIMENTAL. As an illustration of the application of the principles discussed in the preceding section, Thomsen’s measurements for sodium carbonate and cupric sulphate have been plotted in the manner described, and as Thomsen’s data are rather scanty for the mixtures of anhydrous salt and lowest hydrate in each case, redeterminations of the heats of solution have been carried out. For this purpose the very finely pulverised salts were allowed to slowly dehydrate over sulphuric acid at room temperature.The dehydrating salt inisture was frequently repulverised, and whenever a sample was taken for the calorimetric determination a corresponding sample was simultaneously taken for analysis, The calorimetric determinations were made in an ordinary calorimeter with air space and water jacket, the inner calorimeter vessel consisting of gold-plated silver and holding about 500 C.C. The finely powdered salt enclosed in a stoppered weighing bottle and the calorimeter were allowed to remain in a basement room of fairly constant temperature for about twelve hours before a determination was begun, so as to reduce the initial radiation correction to a minimum. The remainder of the experiment was carried out in the usual manner.It is not pretended that the values obtained compare in accuracy with the determinations of Thomsen. It is sufficient for the present purpose that they are comparable amongst them- selves. Table I. contains Thomsen’s experimental results for sodium carbonate. The end-concentrations correspond to I mol. of anhydrous salt per loo mols. water. TABLE I. (Thomsen’s Data). x = Heat of Solution in Calories per Na,C03. xH,O grams. 0 I 2.007 3-234 3‘280 2’965 1’062 4’430 4.889 5’397 5‘956 6‘955 8.048 8’745 10’000 + 5,636 + 2,254 + 12 - 436 - 589 - 1,980 - 1,363 - 5’0% - 6,380 - 7,490 - 8,294 - 10,670 - 12,725 - 139937 - 16,161"48 THE CALORIME'L'RICAL ANALYSIS Plotting y against ,v we get Fig.I, which clearly consists of three straight lines intersecting at two points corresponding to .t' = I and x = 7. In Fig. 2 are plotted the values as redetermined by us. Here the position of the straight line corresponding to mixtures of Na,CO, and Na,CO, . H,O is fised by a large number of determinations. It follows clearly from Figs. I and 2 that the only definite hydrates (besides the decahydrate) whose existence can be definitely detected in this manner are the well-known monohydrate and the less well-known hepta- hydrate. There is no indication of the other hydrates mentioned by Thomsen. As mentioned before, this result agrees with the solubility and thermo- metric data obtained by Wells and McAdam, jun.Thomsen mentions in his original work that he obtained a dehydrate by crystallisation from solutions of sodium carbonate, but this result would appear doubtful. Table 11. contains the calorimetric data on which Fig. 2 is hased. X 0'057 0'449 0.480 0'547 0.570 0.672 c-769 1'174 2.305 3-882 5'677 6.093 7.422 7'950 9'222 9'134 0'22 I y= Heat of Solution per Na,C03. xH,O grams. + 5,020 + 4,440 + 3,880 + 3,600 + 3,540 + 3,350 + 2,930 + 2,570 + 1,140 - s20 - 4s90 - 8,050 - 8,970 - 11,500 - '4,500 - IL+,('Oo - K2,000 In Table 111. are given the heats of solution of CuSO,. xH,O as determined by Thomsen, and in Table IV. the values as determined by ourselves. TABLE 111. (Thomsen's Data). y = Heat of Solution per CuSO, ..rH,O graiiis. 0 r -03 2.227 3.315 q 167 j.000OF HYDRATED SALTS TABLE IV. "49 X 0.067 0.126 O ' I y I 0'274 0'345 0' 393 0.64 I 0.8 10 1.418 1'730 1'777 2'852 3'799 4'25.3 4'366 4'533 4-81 I y = Herct of Solution per CuSO, . .r H,O grams. + Ij,Im + 14,807 + 14,300 + 13,500 + 13,300 + 13,100 + 11,600 + 11,000 + 9,510 + 7,840 + 7,910 + 3,720 + 570 - 660 - 1,020 - 1,860 - 2,600 Fig. 3 shows the result of plotting the data given in Table IV., the experi- nientally determined points being shown by small circles. The combined small squares and crosses correspond to Thomsen's data as given in Table 111. 17000 16000 15000 14000 6 13000 5 (3 p l2000 11000 10000 8 9000 6 0' 8000 v, 7000 L 6000 5000 ,,, 4000 .* 2 3000 2000 8 +I000 0 - 1000 -2000 -3000 -4000 A 0 I 2 3 4 5 x = Mols.H,O per Mol. Anhydrous Cu SO, FIG. 3.-Hydrates of CuSO,. The results are not so regular in this case as in that of sodium carbonate, and the calorimetric data do not indicate with certainty any lower hydrate other than the monohydrate. It may appear curious that the trihydrate,250 THE CALORIMETRICAL ANALYSIS whoseexistence is certain, is not indicated by a *‘ break,” but this is probably due to the fact that the break will be clearly a very slight one (since the angle between the lines at the monohydrate break-point is already very small), and the calorimetric data are neither sufficiently numerous nor exact to indicate it. It is, of course, just possible that in the dehydration the trihydrate is really passed over, or that the velocity of dehydration of the tri- to the mono- hydrate is much greater than that of the penta- to the tri-hydrate. 3. SUMMARY OF RESULTS. I. It has. been shown that calorimetric measurements of the heats of solution in dilute solution of partially dehydrated salt mixtures may be employed as an aid in the discovery of the existence of definite hydrates, although owing to the difficulty of making accurate determinations of the heats of solution this method is not so reliable or convenient as the other well-known methods. 2. It has been shown that in certain cases, of which that of sodium carbonate is a striking example, Thomsen drew conclusions from his calori- metric data which cannot be regarded as justified by these data, and which are in disaccord with other experimental evidence. M USPRATT LABORATO HY 0 F PHYSICAL AND E LECTRO - c H EM 1 STRY, UNIVERSITY OF LIVERPOOL, November I, 1909.

ISSN:0014-7672    

DOI:10.1039/TF9100500244

出版商:RSC    

年代:1910

数据来源: RSC

摘要:

PHYSICAL-CHEMICAL NOTATION. ( A Report pvescirtcd to tltc Scventlt International Coiigwss of Applied Clcewtistry, Towards the close of 1908 the Faraday Society received a letter from Professor Abegg, of Breslau, asking for the Society's help towards securing compliance with the scheme of physical-chemical notation which was adopted by the Fifth International Congress of Applied Chemistry, held at Berlin in 1903." As some of the symbols then proposed seemed hardly likely to find favour with English chemists, the Council of the Faraday Society appointed a sub-committee, consisting of Dr. T. M. Lowry, Dr. F. M. Perkin, Mr. F. S. Spiers, and Dr. N. T. M. Wilsmore, to confer with the com- mittee of Section X. of the London Congress of Applied Chemistry on this question. The committee of Section X.accordingly appointed Dr. J. C. Philip and Dr. G. Setiter to act with the above in drawing up a revised scheme, to be submitted for the approval of the Congress. The symbols now submitted by the sub-committee will be found in column I. of the following table, the symbols adopted by the Berlin Congress being given, for comparison, in column XI. LOIldOlt, 1909.) PHYSICAL-CH EM I CAL SYBIBOLS. I. 11. Nanrh: OF QUANTITY. ill ecltaiticat and Chemical. Length. Area. Volume. Pressure, ordinary and osmotic. Density referred to water. Density referred to air. Viscosity. Surface tension. Atomic weight (0 = 16). Molecular weight (0, = 32). Valency . Intensity of gravity. Concentration in equivalents per litre. Concentration in equivalents per C.C. Time.Equilibrium constant. Velocity constant. Critical quantities-pressure, volume, and temperature. Reduced quantities-pressure, volume, and temperature. Gas constant. * Z. fi Elccktroclz., 9, 686 (1903). 2 j1-5- 3 3 PH Y S I C.4 L- C H E 1’1 I CX L NOT A T I 0 N I. T t c,,, C” C , = c,M u x h L C C, = c,M Q J* x 1J H G I R, I- E E K F K a I1 2n H,SO,, &c. He, Cl’, Ba” &c. PHS~ICXL-CHEJIICAI. SYMHOLS (cortiinzicd). I 1 c,,, CY c,, = c,M Q c, = c,M 1 U x N I W E r FII EC F A A, K Y zn H,SO,, &c. Ha, Cl’, Ba-, &c. H cat ant l TI1 crtnotly rm ntics. Temperature, absolute. Tern pera t ur e , centigrade. Specific heat. Specific heat at constant pressure and con- Molecular heat at constant pressure and stant volume respectively. constant volume respectively.Quantity of heat. Internal or total energy. Free or available energy. Latent or bound energy. Latent heat of change of state. Entropy. Mechanical equivalent. Wave length. Refractive index. Refractivity ( =- N b l , Gladstone). Optical. Refractivity (=-- N * - I . j-, I Lorentz). Molecular refractivity. Specific rotatory power. Molecular rotatory power. Electrical. Current strength. Resistance. Potential. Single potential of an electrode or decom- position tension of an ion. Single potential measured against the nornial hydrogen electrode, the latter being taken as = 0. Single potential measured against the normal calomel electrode, the latter being taken as = 0. Dielectric constant. Faraday constant (= 96540 coulombs). Conductivity. Equivalent conductivity (2).Equivalent conductivity at infinite dilution. Equivalent conductivity of the cation and anion respectively. Velocity of the cation and anion respec- tively in cm/sec in a potential gradient of 1 volt/cm. Degree of dissociation. Transport number. Abbreviations. Twice nornial sulphuric acid, &c. Singly charged positive hydrogen ion, singly charged negative chlorine ion, doubly charged positive barium ion, &c.PHYS I CA L- C H EM I CA L N OTATIOR: 253 With few exceptions the symbols adopted at Berlin have been retained. The following alterations are, however, proposed :- A instead of a for “atomic weight,” the latter being an unsuitable symbol in English owing to risk of confusion with the indefinite article. It is felt to be undesirable to use the same letters as symbols both for the critical and for (‘ reduced ” quantities, seeing that on the reduced system the critical quantities are all unity.t instead of 8 for (‘temperature centigrade.” 6 has not succeeded in displacing t in general use even in Germany. J instead of A for “mechanical equivalent,” reserving A for “free energy.” This is more in harmony with general usage. R, r instead of W for (( resistance.” It will probably be found impossible to secure international agreement in this case. a instead of y for “degree of dissociation ’’ is more in accord with general usage. pr, vk, tk, instead of 7ro, $o, O,, for the critical quantities. In addition to the above alterations some new symbols have been added to the table, in each case the symbol most generally in use having been chosen. This has resulted, in some cases, in one symbol having to represent more than one quantity, e.g., A for (‘atomic weight” and for “free energy” ; c for “ concentration ” and for “ specific heat ” ; t for ‘( time ” and ‘( tempera- ture centigrade ” ; R for (( gas constant,” for (( refractivity ” and for ‘( resist- ance ” ; K for ‘( equilibrium constant ’’ and for “ dielectric constant,” &c. The context would, however, always show for which quantity the given symbol was being used. Also in the cases mentioned it would rarely happen that two of the conflicting quantities would require to be represented in the same equation.

ISSN:0014-7672    

DOI:10.1039/TF9100500251

出版商:RSC    

年代:1910

数据来源: RSC

摘要:

LARGE ELECTRIC FURNACES. RY RUDOLF TAUSSIG, PH.D. (Abstmcf of (1 Patcu rend bcfore Scctioir X of the Seventh Co1igrcs.s if APplirti Cltcriiistr_\; Imuiorr, 1909.) [CObIbIUNICATED BY THE AUTHOR.] The electrothermic industry properly so called, including the processes which are carried out in the electrical furnace at high temperatures, has recently, despite the limitations of its field of applicability, and of its economy, grown to much larger dimensions than were anticipated a short time ago. In the forefront of the industry stands the manufacture of carbide, and it is this which is at present the best developed of the electric furnace processes. Carbide manufacture must now undoubtedly be numbered amongst the large chemical industries. In its technical evolution the carbide industry has at the same time pioneered the development of the electric furnace in the last five years.The single-phase alternating-current furnace, constructed in Sweden by Alby, has been found to be limited to a power capacity of 1,400 kw., and it is not to be expected that this type of furnace could be worked at more than 1,600 kw. Considerable progress has been made by Dr. A. Helfenstein, of Vienna, in the operation of high power furnaces, which is of importance not only to the carbide industry, but also in connection with the manufacture of ferro-silicon and other ferro alloys. At present, according to Helfenstein, the largest power consumption at a built-up electrode amounts to from 2,500 to 3,000 kw., the current being from 30,000 to 40,000 amperes at from 75 to 95 volts at the electrode.In a 3-phase furnace-the only type at present used for such large units-this means a total power consumption of from 7,500 to 9,000 kw., or 10,000 to 12,000 h.p. In the manufacture of carbide a further step has been taken in the construction of double 3-phase furnaces, in which in the same hearth six instead of three electrodes are employed, connected to two separate 3-phase units; the power required is from 15,000 to 18,000 kw., corresponding to a production of from 80 to IIO tons of compact carbide in twenty-four hours. Here we are not, of course, dealing with any real increase of loading, but the case is interesting as showing that the power capacity attainable by arranging 3-phase units side by side is unlimited. Any attempt to increase the power consumption beyond 2,500 to 3,000 kw.per electrode is found to be impracticable unless the furnace is operated by entirely special methods. In open furnaces the heat due to the burning of the gaseous products of reaction is so great that even with less than 3,000 kw. per electrode special 254FIG. I .LARGE ELECTRIC FURNACES "55 protection against the heat has to be provided, both for the workers and for the electrical plant. Simultaneously the gases evolved become a serious nuisance in open carbide furnaces, and more especially so in ferrosilicon furnaces. Smoke is developed disproportionately as the power consumed is increased, and both for sanitary reasons and in order to satisfy police regu- lations it is not desirable to exceed 3,000 kw. per electrode.The principal obstacle, however, to the utilisation of higher concentration of power is the difficulty of satisfactorily charging the raw materials into the furnace. The rate at which materials can be shovelled ilito the furnace by ordinary hand labour cannot be indefinitely increased, with a certainty of covering the electrodes uniformly. At the same time the furnace is never properly covered, which may lead to fuming, i.e., distillation of material due to over-heating. As the capacity of the furnace is increased, the utilisation of the gases produced by the reaction becomes of greater economic moment. In the carbide furnace, 70 to 85 per cent. of the gases is carbon monoxide with carbon dioxide and water, which are easily removable in practice, as almost the sole impurities.256 LARGE ELECTRIC FURNACES The furnace designer is thus led to the need of a closed furnace, and this, together with the adoption of continuous mechanical charging, may solve the problem of concentrating more power at the electrodes, by the avoidance of the smoke nuisance and of excessive radiation of heat, and result in economy by preheating the charge by means of the waste gases, or by the by-production of technically pure carbon monoxide for chemical purposes.I shall now briefly mention those features of Helfenstein’s patents which are of interest in connection with the charging and other general problems of management of the electric furnace. . - - - _ A - - - FIG. 2. Fig. I shows an elevation and section of an 8,000 to 10,000 kw.single 3-phase furnace. About 8 to 10 m. above thc bottom plate is a charging- floor, where the charge is brought, as in blast furnace plants, by tipping wagons to the charging apparatus at regular intervals. The charging arrangement consists of a large mixing chamber which can be closed gas- tight, communicating with the body of the furnace, through which the centrally hanging electrode, of 3,000 to 4,000 kg. weight, passes, being thus surrounded on all sides by the mixture. The mixing reservoir, whichLARGE ELECTRIC FURNACES has a capacity of from 5,000 to 7,000 kg., is fed continuously, as the material is used in the process, through large pipes from the charging-floor above. Wide slits, provided with gas-tight covers, are made in the top of the furnace proper near the mouth of the reservoir, for observation and control of the process.When no more profitable use of the waste gases offers, their immediate application in preheating the charge is carried out by arranging the furnace as shown diagrammatically in Fig. 2. The general form of the furnace is the same as in Fig. I. It is seen that in the upper part of the hearth there is a gas-filled corner space bounded by the naturally sloped surface of the mixture of raw materials; by blowing or sucking air in at nozzles as indicated in the diagram, this space is converted into a combustion chamber, the gases burning in contact with the mixture of materials in the hearth. I shall not at present discuss the proposed means of drawing off the gases, and their application in secondary processes, as my information is partially confidential and patents are pending, but I must be content with having outlined the present position and most recent developments of large electric furnaces, whose principal significance for the future lies in their application to the production of metals-beginning with steel and zinc- in a way that will revolutionise the old metallurgical processes.

ISSN:0014-7672    

DOI:10.1039/TF9100500254

出版商:RSC    

年代:1910

数据来源: RSC

摘要:

TECHNICAL ALKALI CHLORIDE ELECTROLYSIS. BY RUDOLF TAUSSIG, PH.D, Vienna. ( A Paper read before Section X of the Sevetrth Coitgress of Applied Chemistry, Londoii, 1909.) [COMIiiUN'ICATED BY THE AUTHOR.] A briiigcii Tt-mtslatioir by Dr. H. Rov~rs. Very little is published on technical alkali electrolysis in general. In scarcely any other industrial branch is so much secrecy observed as to processes and apparatus. The manufacturers are protected by cartels (" rings ")both as regards the supply of the raw materials (salt) and the sale of the products (chloride of lime and soda). The establishment of new works is thus rendered difficult. Yet the manufacturers are not disposed to exchange information concerning experience gained, not to speak of per- mitting any publication. The antipathy to publication goes so far indeed that, wherever possible, even the application for patents is avoided.A particularly heavy veil is kept over the secrets of works which use mercury cathodes, although secrecy appears little needed in this case. For the many apparently unimportant, and yet most essential devices and experiences, to which success is due, cannot be learnt from a mere visit paid to the works or from publications. We possess only one theoretical research concerning the mercury process, an investigation by Glaser, who studied only the decomposition of potassium chloride, however. At present the mercury process is exclusively applied for the electrolysis of sodium chloride. The following lines contain the chief results of the only investigations carried out in this field due to Taussig and to Taussig and Aigner.These investigations are confined to the chlorine cell, i.e., to the decomposition of sodium chloride, with the aid of platinum and mercury electrodes and the formation of chlorine and of sodium amalgam. APPARATUS. The apparatus employed comprised the following devices :- I. The appliances for supplying and regulating the electric current and for measuring the intensity and electromotive force of the current passing through the electrolyser, as well as the e.m.f. of the polarisation current. 2. The electrolyser. 3. Appliances for maintaining the mercury circulation. 4. Appliances for taking amalgam samples and for estimating the sodium. 5. Appliances for maintaining and controlling the circulation of the 6.Appliances for withdrawing the chlorine from the cell and for its 7. For maintaining certain temperatures in the electrolyser. Ad I. The sources of current were storage batteries of 8 and 24 volts brine. absorption ; and 258CHLORIDE ELECTROLYSIS 259 The battery leads (Fig. I) were taken to a large double pole-switch, which either cut the apparatus out or joined it to the 8-volt or to the 24-volt battery. FIG. I. Ad 2. The electrolyser (Fig. 2) was a glass beaker, IIO mm. in height, 60 mm. internal diameter, 2.5 mm. wall thickness. The wall was perforated immediately above the bottom of the beaker ; a rubber stopper closed this hole of 11 mm., and the mercury tubes passed through this stopper. The feed tube a was the lower of the two and consisted of a rather wide pipe, tapering towards its opening and bent in a horizontal plane to a semicircle. The mercury, introduced under pressure, issued from the opening in a tangential jet, which agitated the amalgam.The mercury layer had a thickness of 15 mm., and the inner mouth of the discharge tube b (which was less wide than the feed tube) for the amalgam was immediately below the surface of the mercury ; the short discharge tube was bent somewhat like an S, the outer end lying at a higher level than the inner end. Another perforation of the glass was 70 mm. above the bottom and at cp" to the first aperture ; this second perforation was closed by a stopper of the same size, holding the wide discharge pipe for the chlorine and for the spent brine. I FIG.2. The large rubber stopper which 5erved as cover for the beaker was provided with six perforations. The glass tube forming the anode support260 TECHNICAL ALKALI passed through the central hole. The anode consisted of a platinum spiral, strengthened by two ribs and soldered to a shorter platinum wire, which was fused into the glass tube; the latter contained some mercury and the terminal wire. The distance between the two electrodes was always 19 mm. during the current yield determinations. The other perforations admitted the two legs of a glass coil for cooling or heating the electrolyte, a thermo- meter, the brine supply pipe, ending immediately above the kathode, and a short pipe joined to a water-gauge, by the aid of which the internal pressure was reduced by 7 cm.of water. This was done in accordance with the technical practice to withdraw the chlorine under slightly reduced pressure. Ad 3. The following apparatus regulated the circulation of the mercury :- (a) A glass trough, serving as mercury reservoir, capable of being raised and lowered. (b) A glass tube, 2 mm. in width, drawn out to a point and adjustably fixed on a stand ; rubber tubing connecting this glass tube with the amalgam dis- charge pipe of the electrolyser, and the level adjustment permitting of altering the rate of discharge of the amalgam. The latter flowed either through a funnel into the decomposition cell, or into a sample glass. ( c ) The amalgam-decomposition cell, a stout glass beaker, I litre capacity, was provided with a stirrer and charged with hydrochloric acid of 15' B6. ; the mercury was discharged through a lateral pipe near the bottom.Before returning to the mercury tank, the mercury was twice passed, in drops or in a thin jet, through diluted hydrochloric acid and finally through water. Ad (a). Fig. 3 illustrates the arrangement adopted for regulating the rate of the mercury feed to the electrolyser. The pure mercury entered through FIG. 3. the funnel S, and the cock was opened sufficiently to ensure that at least as much mercury flowed out of the reservoir R as left it through the feed pipe (for the electrolyser) L, ; L is an overflow pipe. The reservoir (15 by 10 cm. base) stood on a board which was suspended over pulleys; the weights Q and QI served as counterpoises. Ad (b). In Fig.4 (front and side elevations), E is the electrolyser which is cemented to a block of wood, 18 cm. in thickness, the wood itself being cemented to the base. S is the stand ; A is the arrangement by means of which the amalgam is sent either into the test-glass G, or into the amalgam receptacle GI. A d 4. In conducting the determination of the sodium percentage in the amalgam, the amalgam discharged during a definite period, ranging fromCHLORIDE ELECTROLYSIS 261 10 minutes at the lowest to 25 minutes at the highest, was collected in the beaker G, the time being read off within a quarter of a second. The amalgam FIG. 4. was shaken with an excess of titrated hydrochloric acid in a stoppered bottle of I-litre capacity,land the solution titrated back with caustic soda and phenol- phthalein ; I cm.3 of the acid absorbed corresponded to 0'01 grani of Na in the mercury.m FIG. j. A d 5. Considerable attention was paid to the important circulation of the brine (Fig, 5). In accordance with the usual practice, the brine feed pipe had its mouth immediately above the mercury surface (cJ Fig. I). A capillary C was inserted in the feed pipe H so as to obtain a rate of flow of not more than 3 cm.3 per minute. The accurate regulation was effected byt a- 9 CJ 0 rJ 0 0 - --- -.+*.- G - -L.< g - - . - --.-g . _ . _ . _ _. -..; ______.___ -.% -.*-- - t Concentration of AmaJqom PLATE I. Current Efficiency as function of the amalgam concentration. Efficiency in per cent. of the theoretical. Concentration of amalgam, per cent.of Na in the Hg. Re-formation of amalgatu, loss of sodium per minute, expressed in tenths of a milligramme. Volts across the cell. Current intensity in amperes. Polarisation in volts.c 0 ti c I T I 2 8 5 6 cut$& ~ d ~ s l h y I d9-Y - - - - - - - - - - - - - - - - - - - - - - - - ---------01e987 I ! I I I I 6 Re- Formation of Amalgam 9 , 2 ? I 3112 3,1Z : 1.3 3 " g:; _ _ _ _ & o ____.___- --0--- _ _ _ _ & - , _ _ _ _ e--- -. -.-8+!"~?? - - - - _ _ * - - o 9 "-6 V V II I i 1 Current efficiency as function of the temperature. Efficiency in per cent. of the theoretical. Temperature in degree Cent. Re-formation of amalgam, loss of sodium per minute expressed in tenths of a milligramme. Volts across the cell. Current intensity in amperes. Polarisation in volts.c .'o''o,ol E s PLATE IV. Current efficiency as function of the current density and of the amalgam concentration. Efficiency in per cent. of the theoretical. Concentration of amalgam, per cent. of Na in the mercury. Re-formation of amalgam, loss of sodium per minute expressed in tenths of a mflligramme. Volts across the cell. Current density in amperes per dm. Polarisation in volts.PLATE V. Current efficiency as function of the current density. Efficiency in per cent. of the theoretical. Concentration of amalgam, per cent. of Na in the mercury. Rate of circulation of mercury in cm.3 per minute and per dm.2 of kathode surface. Re iormation of amalgam, loss of sodium iii tenths of a milligramme per minute and per dm.' of kathode surface. Current density in amperes per dm.' of kathode surface.CHLORIDE ELECTROLYSIS 263 adjusting the pressure in the brine tank V, a bottle whose stopper was fitted with two perforations ; connection was thereby established either with the atmosphere, or through g and S with a vacuum vessel whose controlling pressure gauge was filled with coloured brine.The spent brine flowed through the pipe R into a calibrated cylinder M, from which it was with- drawn at intervals. As indicated in Fig, 5, V acts as Mariotte bottle, the cock h being open. When lz is closed, and g raised above the level of the brine at N, the pressure above the brine in V can be reduced through the suction pipe S by the water-jet pump. The vacuum was adjusted by altering the depth to which the tube T dipped into mercury.Ad 6. The chlorine was discharged together with the spent brine through the pipe R (Fig. 5). The chlorine mixed with air was sucked through three large bottles, twice through milk of lime, once through concentrated caustic soda, under a vacuum of 7 cm. of water ; the electrolyser itself was, there- fore, under this partial vacuum, as alrcady stated. Ad 7. The temperature regulation in the electrolyser was effected by circulating hot or cold water, cold brine, or sometimes superheated steam through the glass coil. The mercury and brine were themselves preheated or precooled with the aid of a copper coil and water or ice, the brine or mercury being sent through glass coils. As this temperature regulation had to be very accurate, the cooling coil was not directly joined to a tap in the water-supply pipe, but to an intermediate vessel.The results of the experiments are summed up in the curves of Plates I. to V., and in the tables which follow them. The curves show current efficiencies, expressed as functions of various quantities. RELATION BETWEEN POTENTIAL DIFFERERCE AND CURRENT DENSITY. Electrode Distance : 19 ~ n m . Mean Temperature : 16.8' C. At - 0.49 amp./dm." the P.D. was 3.34 volts. 099 ,f ,, 3'32 ?7 1.95 > * > > 3'53 9 9 3'41 9 9 9 , 4-30 B9 5'2.1 9 9 ,9 4-93 ), 6.99 ,? 9 , 4-98 ? 9 8.71 ,, 77 5.15 , 9 10.34 19 ,> 5'42 9 ) 13-82 9 7 ,, 6.06 ,, 17'67 , t ,I 6'59 , 9 35-00 ) I 9 , 8-10 ,, RELATION BETWEEN POTEXTIAL DIFFEREXCE AND TEMPERATURE. Electrode Vistaizce : 10 mm. Meaii Citrrent Demity : 7-00 amn~.ldrn:.At- - - 2'5 ,9 5'90 ,, + 2.8 > 7 5'70 9 , + 7'3 9 9 5'50 9 9 + 17'0 9 ) 4'98 ?) + 30'0 77 5-02 ,, + 50'3 ,, 4'35 9 ) + 58'9 ,, 4'24 9 ) + 82.9 ?, 3-78 9 , + 90.0 9 7 3'74 ?) + 10g.o ,7 3'70 ,) 5*oo the P.D. was 5.93 volts.264 TECHNICAL ALKALI RELATION BETWEEN POTENTIAL DIFFERENCE AND AhfALG.4M CONCENTRATION. Electrode Distance : 19 irtm. Mean Current Density : 7.00 aritl)./dm:. With- Mean Temperature : 16.6~ C. 0'0280 per cent. of Na in the amalgam, the P.D. was 4.93 volts. 000263 ,, 9 9 ? 9 9 , 4'97 ?, 0'0200 ,, 9 , 9 ) ,, 4'98 ?, 0.0094 ,, 9 9 9 ,? 4-98 9 , 00062 ,, 3 , > ) 9 , 4'72 99 0*0141 ,, ,, 9 9 7, 4'94 >) RELATION BETWEEN POTENTIAL DIFFERENCE AND RATE OF CIRCULATION OF THE ELECTROLYTE. Electrode Distance, 19 mm.; Mean Cwrent Density, 6.95 arnp.ldm: ; Mean Temperature, 16-2' C . N'ith a circulation of- o*oo cm.3 per minute, the P.D. was 4.97 volts. 0'27 ,, 9, ?? 4'97 ,, 0'75 ?) 9 , 9 , 5-02 9 , 1'02 ,, 9 , 1, 4'97 7, 2'23 ,, 9 , ? 9 4.9' J ? RELATION BETWEEN POTESTIAL DIFFEREXCE AND ELECTRODE DISTANCE. ilIeait Current Density, 35 nmp.ldnt: ; Alean Tena$erature, 22' C . With an electrode distance of- 3 mm. the P.D. was 5-76 volts. 5 ,, ?, 6.35 ? 9 7 9 , ,J 6'67 ,I 12 9 , 9 , 7.20 ,? 15 ,, ,? 7'75 ) Y 2o J P ,? 8-17 >, 30 99 ) 9 8-50 ?, 40 1, 9 , 9'70 9 9 The apparent slight discrepancies in the results of these tables, corre- sponding to small differences in the potential difference, amounted to a few hundredths of a volt only, and should not be overrated ; those small diff ereiices were fair estimates.All the experiments were made with the same anode, a platinum wire of 0.90 mm. diameter, spirally wound in a plane and radially stiffened by other wires. The surface of the anode was hence approximately 18 cm.*, and the anodic current density 14 times that of the kathodic current density. The current density of the anode was, of course, not without influence upon the potential difference. Yet the increase in the potential difference by an increase in the anodic current density will not progress at the sa.me rate as it would do with an equal increase in the kathodic current density, in cases where the kathode is a more or less plane surface, while the anode may be shaped in a manlier so as to admit of a ' point effect.' When, moreover, a gas is generated at the anode, which is The anode weighed 8.gBoo grams.CHLORIDE ELECTROLYSIS 265 hardly to dissolve in the electrolyte as in this case, an anode of very large surface would be unfavourable, since the anode product would be liberated in too fine a state of subdivision.IXDUSTRIALLY APPROVED PROCESSES. Four types of technically applied processes may be distinguished :- I. The old Castner-Kellner cell (rocking apparatus at Oldbury). 2. The Kellner apparatus (compressed air, at Jajce). 3. The Kellner-Solvay apparatus (cup wheel, at Jemeuppe). 4. The new Castner-Kellner apparatus (Archimedean screw, at Weston Point). I. The Old Castvier-h'ellrrer Cell. This oldest type of cell is sufficiently known. The anodes of the cell con- sisted of carbon, the kathodes of iron-wire grating.The fact that various detailed descriptions of this type of cell have been published will suggest even to those not familiar with the subject that the apparatus must already have been superseded, and that is indeed so. At present only apparatus are constructed which take at least ten times the amount of current of the old Castner-Kellner cell, The rocking cell is divided into three compartments, and the mercury is moved by means of an eccentric which is attached to the side of the cell, and which alternately raises and lowers that side. The movement is so small and slow as to be scarcely perceptible. The disadvantage is that the units are small; they can only take 400 or 500 amperes. Enormously large buildings are required, all leads and pipes (for current, brine, lye, and chlorine) become very long, com- plicated, and expensive, and the superintendence of the large spacc (there were about 600 of these apparatus at Weston Point) is difficult.2 . The Keltrter Apparatus (Compressed Air Type.) This is the most interesting apparatus. It consists (cf. diagram Fig. 6) of three compartments, joined by siphons, the chlorine cell being in FIG. 6.-Kellner (Compressed Air) Cell. the middle, while the caustic soda compartment was in the middle of the old Castner cell. The two alkali compartments are provided with wells, into which the vessels for the compressed air dip. The mercury is driven (by the air) from the one compartment into the other, taking up sodium in the central compartment and giving it up again in the last.The anodes of platinum are mounted in electrode boxes of cement, which I introduced six years ago, and which have answered better than the previously applied clay boxes. The anodes themselves are wire gauze sheets, of 50 by jo mm., weighing I gram each, including the platinum pin ; the latter is fused into a glass tube charged with mercury, into which a stranded copper wire is266 TECHNICAL ALKALI lowered. Every chlorine cell contains six electrode boxes, each with eighty- eight pieces of platinum wire gauze, giving a total of 518 sheets of platinum 'weighing 500 grams per 4,000-ampere cell. The kathodes are grids of cast iron. The current passes from the anode through the brine to the mercury or the amalgam ; the sodium ions con- tained in the amalgam carry the current further through the caustic soda to the kathode.There is a shunt for the current-a short circuit between the mercury and the iron. This has long been known, and the respective patents have long expired ; but the object of the device may be explained. The shunt is to prevent loss of mercury. The chlorine held by the brine reacts, in the chlorine compartment, on the sodium of the amalgam, and some sodium chloride is again formed. The sodium ions which have taken part in this reaction are wanted in the alkali compartment, and in their absence mercury would participate in the current conduction, mercury oxide would be formed, and some mercury be lost. The shunt provided by the short circuit rapidly and almost instantaneously decomposes the.amalgam. The mercury is hence quickly regeneratcd and enabled to absorb more sodium ; the arrangement therefore admits of applying very high-current densities. It is Kellner's greatest merit that he has drawn attention to the ad- vantages of working with high-current densities at a time when low electromotive force was the only criterion of the value of a cell. He recognised that other factors, notably simplification of the operations by putting higher loads on the electrodes and consequently increased output, are equally important, The short-circuit cell may be adapted to various conditions; it is chiefly intended for cheap water-power however. 3. The Kelliter-Solvay Apparatus (Cup-wheel). The apparatus in use at Jemeuppe (Belgium), Brescia (Italy), Lubimoff (Russia), consists of two parallel troughs, inclined and communicating with one another, in which a cup-wheel keeps the mercury in circulation.This type of cell is constructed in the largest units. Originally designed for 6,000 amperes, it is now built for 10,000, and even 15,000 amperes. The cell is fitted with a weir (D.R.P. No. 100,560) over which the amalgam, which is chiefly formed near the surface, is carried. Platinum wire gauze anodes are used; they are larger, however, than those already mentioned, being cp x cp mm., and the gauze is, moreover, interlaced, the work being done by the experienced lace-makers of the Brussels district. The works at Jemeuppe rely on steam ; at Brescia water-power is utilised. 4. The New Castner-Kellner Apparatiis (Archinzedean Screw).The chief difference between this type and type 3 is that an Archimedean screw replaces the cup-wheel in moving the mercury. The type does not otherwise constitute an improvement on the Solvay apparatus. It works with smaller current densities, and is designed for about 4,000 amperes; this figure might be raised, but the present type is not likely to prove suitable for the large units of the Solvay cell. The apparatus is exclusively intended foreexpensive power. It works with low-current densities and very low e.m.f., and the carbon electrodes are arranged according to the British Patent No. 14,133 of I ~ Z . Blocks or plates of carbon are placed between the copper bars which act as leads, and the parts are bolted together.CHLORIDE ELECTROLYSIS 267 The Sodium Chloride.-The sodium chloride should, particularly where carbon electrodes are applied, be freed from sulphates.At Weston Point the brine flowing into the works used to be purified with lime and soda (by the Castner process) and then evaporated ; the resulting salt was further washed with concentrated brine in order to remove all the sulphates. This method gave too much trouble. At present the brine is, at Weston Point, purified in a similar manner and then sent to the cells ; the impoverished brine is deprived of its chlorine by means of lime and then allowed to run to waste. The Caustic Soda.-The caustic soda, the chemically pure caustic of the trade, is used chiefly for the production of metallic sodium by the Castner process.The Materials.-The choice of materials is an extremely iinportant problem. When the material out of which the cells are built up turns soft or leaky, losses of mercury will arise, and then the process becomes illusory. With low-current density the temperature in the cell will not grow high, and the strength of the cell frame will not be severely strained. The caustic lye compartments and the siphons are most exposed. Concrete finished with cement is almost the universal cell material at present ; slate and other materials have been abandoned. The above outlined processes have so far alone been in the field. Of recent inventions only those of Wildermann, Bell, and Rink, and a few diaphragms deserve mention. The Wildermairn process is based on the British Patents No.18,958 of 1898, No. 22,90.2 of 1900, and No. 9,803 of 1902. The mercury is contained in troughs which are so piled upon one another, ribs of the trough above entering the trough below, that they form a diaphragm between the amalga- mation and the decomposition compartments. The mercury does not cir- culate, but is agitated on the chlorine side. The method permits of applying extraordinarily high-current densities without risking the solidification of the amalgam or the oxidation of the mercury. The buoyancy of the specifically lighter amalgam takes charge of the transport of the sodium ions from the chlorine cell to the caustic compartment. The whole apparatus is built of iron and liiied with a special ebonite. Carbon anodes can be used in spite of the high-current density.The current density at the mercury may amount to 30,40, and even 60 anips./dtn.* ; at the carbon anode it will only be about 10 amperes. Owing to the very small quantity of hypochlorite formed, the carbons are said to have proved very durable in three years' working. The floor space wanted is only 4 cm.* per ampere, while the old Castner-Kellner cell requires 30 to 40 cm.*, and the Jajce cell II cm.*. The Wilderinann cell has so far been constructed for 2,200 amperes. At a current efficiency of 93 per cent. and an e.m.f. of 5 volts, it requires 3-58 kw.-hours per kg. of caustic soda, at 4'5 volts 3.2 kw.-hours. The Bell cell has been tried by the Pennsylvania Salt Manufacturing Company at Wyandotte. Definite iiiformation is not available.The Bell patents are the British Patents No. 20,542 of 1895, No. 11,133 of 1896, No. 25,890 of 1899, and No. 10,655 of 1902. They also make provision for preventing the contamination of the mercury, which is spread on a diaphragm, by the impurities dropping from the carbon anode. Soap Diafilzragms.--The Kellner soap diaphragm (Ber. DeufscJt. Chent. Ges., 1893, p. 1159) is to be tried in the electrolytic works at Briickl in Styria. Those who have worked with soap diaphragms will have their doubts as to the possibility of their continued use ; the chlorine acts on the soap, and the VOL. V-T10268 CHLORIDE ELECTROLYSIS soap is soluble in the concentrated brine to a sufficient amount to cause various difficulties.':: The Rirzk process (Fig. 7) has only been tried in experimental installations.A larger plant is now being built. The chief advantage is apparently that the diaphragm does not allow the impurities in the carbons to pass over to the mercury, and that the latter can be cleaned without opening the apparatus. A'et Electrode FIG. 7.-The Rink Apparatus. The chief disadvantage will probably be found in the intense agitation of the mercury, which may lead to losses of mercury and may demand an unusual amount of power. The choice of the best material for the net electrodes is not yet decided. Baiyta Diaphragm.-The Kaliwerke Aschersleben have for some time been using a cell which I adapted to operations on a large scale as early as 1904 in the laboratory of Kellner. The principle is that a vessel closed above is placed within a shallow kathode vessel. A layer of baryta connects the anode and kathode space ; these diaphragms offer the advantages of great durability and of small rcsistance. The Townserzd cell is said to answer very well in England and America. The Electrolytic Alkali Company, Ltd., of Middlewich, has improved the Hargreaves-Bird process by producing bicarbonate instead of crystal soda. There are both technical and commercial advantages in this change which, however, appears to have brought about a decided fall in the price of bicarbonate. In spite of the occasional overproduction of chloride of lime, which is strongly felt just at present in two fields, neither means nor pains are spared for working out new processes, and new plants arise, while those in existence are being enlarged. Yet the largest consumers of chloride of lime, the bleach works for cotton and linen, and especially for cellulose, have made them- selves independent of the market, either by building electrolytic works of their own, or by diminishing their consumption of chloride of lime with the aid of rational methods of bleaching. These facts prove that the consumption of chlorine and of chlorine compounds is increasing owing to their low prices. * The above-mentioned doubts were evidently justified. Kellner's rights as claimed in E.P. 7801 of 1894, were bought in 1904 by the Bosnische Elektrecitats Aktien-Gesellschaft of Vienna. Apparently all efforts to find a practical cell with the soap diaphragms were unsuccessful, as the said Company erected baryta diaphragm cells at Bruckl.

ISSN:0014-7672    

DOI:10.1039/TF9100500258

出版商:RSC    

年代:1910

数据来源: RSC