A PHYSICO-CHEMICAL STUDY OF THE COMPLEX COPPER-GLYCOCOLL SULPHATES. BY J. T. BARKER, B.Sc.::: (From the Muspratt Laboratory of Physical and Electro-Chemistry, University of Liverpool.) ( A Pqkr read hcfore fltc Farndny Socieb O I L T u c s ~ ~ J , , December 17, 1907, DR. F. MOLLWO PERKIN, TREASURER, in the Chair.) It is well known that addition of glycocoll to aqueous solutions of copper sulphate produces a fine blue colour, similar in general character to that produced by excess of ammonia. That the concentration of the cupri-ions has been lowered by the presence of the glycocoll is rendered probable by the fact that caustic potash does not precipitate cupric hydroxide from solutions containing moderate amounts of glycocoll, whereas potassium ferrocyanide and ammonium hydrosulphide throw down precipitates of cupric ferrocyanide and sulphide respectively. It seemed probable that the reduction in the concentration of the cupri-ions is caused by the formation of complex cupri-glycocoll kations.The experimental work described in the present paper was undertaken with the object of investigating this question. I. E LECTROMETRIC M EASUREXIENTS. In order to arrive at some idea of the degree of complex formation, the following preliminary measurements of potential were made. A series of solutions &th molecular normal with respect to copper sulphate, but respec- it it ia 2 q 1 0 tively -) -, - with respect to glycocoll, was made up. By Poggendorff's Y compensation method, using a slide-wire bridge and a Lipprnann capillary electrometer, the potential differcnce between a clean copper rod and each of these solutions was determined.For this purpose each copper electrode was connected through a KCl solution with a normal calomel electrode, and the cells so constructed were measured with and against a standard cadmium cell in the usual manner. Taking the potential of the calomel electrode as +0*56 volt, and the E.M.F. of the cadmium cell as 1.0186 volt, the results shown on page 189 were obtained at 17OC. In calculating these values the potentials at the liquid junctions have been neglected (as a first rough approximation). o-oooIq8T c By means of the formula T== Log 2 we can now obtain 2 C, approximate values for the ratios of the cupri-ion concentrations in the several solutions examined.In the above formula 7r denotes the E.M.F. of a cell such as- Cu [ CuSO, I KCI I CuSO, + glycocoll 1 Cu, and c, and c, denote the respective cupri-ion concentrations. * Communicated by Dr. F. G. Donnan. r 88STUDY OF COPPER-GLYCOCOLL SULPHATES 189 1 2 5 Solution. 48 I 9 3 .- Concentration of CuSO+ It I 0 - n - I 0 It I 0 - 11 1 0 - 2oncentration of Glycocoll. Potential of Copper Electrode. Thus for the cell Cu I '5 - CuSO, I KCl I & CuSO, + It glycocoll I Cu Calling the concentration of the cupri-ion in the 2 --.CuSO, solution 100, I 0 I 0 T = 0'5 58 - 0'549 = 0'009 Volt. I 0 we obtain in this way the following table of relative values- TABLE I. h1ol;ir Ratio of Glycocoll to CuSO+ 1 Relative Coiicentratioii oi Cii.*-ion. These figures, though not pretending to be very accurate, suffice to show the progressive decrease of the Cu--concentration on continued addition of glycocoll, and appear to warrant the assumption that with a large excess of glycocoll the cupri-ion will be practically completely converted into some complex ion (or neutral compound).We shall assume first of all, as seems most probable, that a complex cupri- glycocoll ion kation is formed, and that its formula may be represented as CuG;., i.e., that it contains x mols. of glycocoll for every atom of copper. If the glycocoll be present in large excess relatively to the copper sulphate, we may assume, with a fair degree of probability, that practically all the copper sulphate will be converted into complex copper-glycocoll sulphate, and that, to a first approximation, we may take the final concentration of the glycocoll as equal to its initial concentration. Furthermore, if the solution be pretty dilute with respect to total dissolved copper salts, the complex sulphate (or sulphates) may be regarded as completely ionised, in which case the final molar concentration of the cupri-glycocoll ion will be equal to the initial190 A PHYSICO-CHEMICAL STUDY OF THE molar concentration of the copper sulphate.Let us suppose that the com- plex ion CUG;. dissociates (non-electrolytically) into glycocoll and cupri-ions. Denoting molar concentrations by square brackets, and writing i for initial total concentration of copper sulphate, we have- [CU..]~ . [G].r= k [CUG,**], = ki,. For another solution- [CuamJ - [GI: = ki,.Whence, dividing and taking logarithms- Although [Cu-1, and may be very small, their ratio is a definite quantity, which is found by measuring the potentials of a copper electrode in each of the two solutions, and then applying the formula- The only unknown quantity in Equation ( I ) is, then,x. In order to obtain the most accurate values, two corrections must be applied to Equation (I). In the first place, an allowance must be made for the amount of free glycocoll removed from the solution as complex ion ; and secondly, if the complex copper-glycocoll sulphate be not con~pletely ionised, the concentration of the complex copper-glycocoll ion is not equal to the initial total concentration of copper sulphate. The second correction will be dealt with later. Equation ( I ) , with the first correction, takes the form- In solving this equation, an approximate value of x is first obtained from Equation (I), and then the value of x which satisfies ( 2 ) is found by successive approximations.In the case of the preliminary data already given, any potential differences existing at the liquid junctions were ignored. These potential differences can probably be for the most part eliminated by comparing only solutioris having the same total copper content and a varying, though very large, relative excess of glycocoll, for in this case the two solutions will contain practically only complex sulphate, and that of practically the same concentra- tion in both cases. I t will be seen that the method here employed is substan- tially that first introduced by Bodlander.The results of the first measurements are contained in the following two tables. The E.M.Fs. of the concentration cells have been calculated frotn direct measurements of cells of the type Cu [ CuSO, + glycocoll I 3.5 11- NaNO, 1 calomel electrode. For the rest, the values of x given in Table 111. are seen to be considerably higher than those in Table 11. Probably only the values in Table 111. are deserving of weight, since these are derived from measurements of pairs of solutions of equal total copper content. More accurate measurements were rrow carried out, in which every effort was made to eliminate disturbing influences. The calomel electrode was dispensed with, the E.M.Fs. of the concentration cells being directly The value 1-35 is evidently too low.COMPLEX COPPER-GLYCOCOLL SULPHATES 191 TABLE 11.-Temperature 13" C .n - CuSO, + 212 glycocoll - C~SO, + glycocoll 5 C~SO, + 212 glycocoll C~SO, + zn glycocoll I 0 0 n I 0 0 I 0 0 I00 First Solution. 0.0138 om030 0.0421 0'0135 2- c u s o , + ~glycocoll -K cuso, + f glycocoll 2- c u s o , + ~glycocoll 2- c u s o , + ; glycocoll 200 200 2 00 200 CUSO, + 21t glYCOCOl1 I 0 0 5 CuSO, + glycocoll 200 E.M.F. of Corn bination. Second Solution. 0'0391 4'59 0.0289 3-39 x Calcu- ated from Equation (1). 2'62 1-35 2'97 2.58 TABLE 111.-Temperature 13" C. First Solution. 2- c u s o , + ; glycocoll -2- c u s o , + ; glycocoll 1 0 0 I00 -2- c u s o , + 12 glycocoll 200 2 Second Solution. I measured, with 3-5 n NaNO, solution as connecting liquid.The concentration cell waEs cnmhined with ;1 standard cadmium cell. and the E.M.F. of this com- bination determined, with the concentration cell acting both with and against the cadmium element. From these measurements the E.M.F. of the concen- tration cell was calculated. The means of the two values so obtained are given in the following table. As the E.M.Fs. of the concentration cells do not amount to more than 3-4 hundredths of a volt, and small errors in the values of the E.M.Fs. produce considerable errors in the values of x, it was found necessary to introduce corrections for any inequality of potential of the two copper electrodes when dipping in the same copper solutions. This inequality of potential did not ever appreciably exceed I millivolt. On making this correction, it was found that the values whose means are given in the following table did not differ by more than a few tenths of a millivolt, In order to eliminate errors due to the liquid potentials or to a varying degree of ionisation of the complex sulphate, only solutions of the same total copper content were compared, and these solutions contained large relative excesses of glycocoll.I92 A PHYSICO-CHEMICAL STUDY OF THE Since i, = i, = i, equations ( I ) and (2) reduce to- Conc'n.of CuSO4 in both Solutions. 200 It 250 It 250 it L o g w I , + . ~ L o g [ G L o . . . . . [CU"] m2 TABLE IV.-Final E.M.F. Measurements. [CIP p 2 2 It 12 I 4 2 5 4 2 5 2 It 3 E X F . of Concentration Cell. 0.033 5 0.0339 0.0355 0.03 I 8 0.0309 0.0327 reinperature 19" 19" 20'5O 20.5' 21° 19" Mean values ...... .r Calculated from (3). 3'85 4-12 4-05 3'63 3'53 3'76 3.82 * * (3) ' (4) x Calculated from (4). 3'75 4-00 3'95 3'54 3'45 3-65 3'72 It will be observed that the ratios of glycocoll to copper sulphate are the same for the different pairs of solutions, so that any pair of solutions could be obtained from a more concentrated pair by dilution. This was done with the intention of seeing whether the value of x varied with the dilution, the ratio of glycocoll to copper sulphate being constant. No variation within the above range of concentrations can be said with certainty to occur. The E.M.F. measurements point to the existence of complex ions of the formula [CuG4]" and their dissociation-products. To this ion corresponds the complex sulphate [CuGJSO,.The fact that x comes out somewhat less than 4 is probably due to the partial dissociation of the complex ion CuG;. into less complex ions such as CuG,, &c., i.e., the elementary Cu..-ions are converted by the excess of glycocoll partly into complex ions containing less glycocoll than CuG,". This conclusion requires to be supported by evidence obtained from some independent method, and with this object in view the freezing-point measurements described in the next section were undertaken. 2. FREEZING-POINT MEASUREMENTS. A few preliminary measurements of the freezing points of aqueous glycocoll solutions gave as a mean value for the molecular weight 73.5 (theoretical value 75), thus confirming the already known result that glycocoll exists sirbsfnnfially as simple molecules in aqueous solution.COMPLEX COPPER-GLYCOCOLL SULPHATES 193 In order to investigate the complex formation, the freezing-points of a series of strong glycocoll solutions of gradually decreasing concentration were determined, and the rise of freezing point produced by the addition of small quantities of copper sulphate to these solutions measured very care- fully.Let y denote the net number of active individuals removed from the solution per mol. copper sulphate added. As before let x denote the number of glycocoll molecules which combine with the Cu-atom to form a complex. We shall now assume that practically all the copper sulphate added is con- verted by the large excess of glycocoll present into complex sulphate and that at the fairly high dilution used the value of van't Hoff's factor i for the complex sulphate is the same as that for copper sulphate of the same total molar concentration. Then, per gram.mol. copper sulphate added, i new individuals enter the solution, whilst x individuals (glycocoll molecules) are removed. If the solution employed is so dilute with respect to total copper that we can assume complete ionisation of the complex or simple sulphate, x = y + 2. The practical range of this method of procedure is limited by the fol- lowing considerations : The rise of freezing point actually measured being dependent upon the amount of CuSO, present, as much of this salt as pos- sible must be added, in order to reduce the percentage error of the readings. But as it is imperative to have the glycocoll in large excess of the copper sulphate to ensure as complete as possible a formation of complex salt, the amount of copper salt that can be added will depend on the solubility of glycocoll at the temperature of the freezing points.The cryohydrate point of glycocoll was found to be approximately - 3", so that at this temperature the saturated glycocoll solution must contain about 2.3 grms. of glycocoll per 20 grms. water. In the experiments to be described the amount of glycocol! taken varied from 1.2 to 2.1 grms. per 20 grms. water, whilst the rises of freezing point observed varied from 0 - 0 2 1 O to 0.0880. Supposing the probable error of any one reading to be O'OOI~ and of any measured rise to be 0 ~ 0 0 2 ~ ~ the percentage error of the latter must vary from 9 s per cent.to 2-3 per cent. In order to obtain values of x of sufficient accuracy for our purpose it is clearly necessary that the rises of freezing-point must be determined very carefully. In the apparatus used the cooling bath of ice and brine was sur- rounded by a vessel containing finely crushed ice, the outer walls of which were enveloped in felt, so that its temperature did not vary as much as &* during a series of measurements. The stirring was done by an automatic stirrer driven at a constant rate, the Beckmanii thermometers were kept in ice for several hours before a measurement, and for every series of measure- ments with one solution the temperature of the ice-brine bath was carefully adjusted so as to give a convergence-temperature as nearly as possible equal to the freezing-point to be measured.The supercooling was kept within the limits O'I~--O'~". The following example well shows the general accuracy of the results- Freeziizg-Point of Piire G~COCOII Solution. Hence x -i = y, or x = y + i. Temperature of Cooling Bath. 1 Freezing Point. 4'5" 4 5" 4'5" - 4'5" 2'393 2'390 2'392 2'394 Mean = 2-392 - I Supercooling. -I--- 0.178~ 0' 150" 0.167" 0.162'I93 A PHYSICO-CHEMICAL STUDY OF THE Temperature of Cooling Bath. - 4'5" - 4'5" - 4'5" Freezing-Points of Glycocoll-copper Sulphate Solution. Freezing Point. Supercooling. ~ 2.415 0' 175" 2'413 0.171~ 2-412 0.157" - Mean = 2.413 Rise of freezing-point = 0 * 0 2 1 O . Concentration of copper sulphate =0.000886 gm. mols.per IOO grms. water. i for copper sulphate at this dilution = 1-89. Total no. of mols. glycocoll present in the solutioii per mol. CuSO,= 89.5. Calculated value of x = 3'17. The following table contains the results of the freezing-point measure- ments. TABLE V.-Freezing-poirat Measurements. Concentration of CuS04 in grm. mols. per 100 grnis. water. 0.000886 0.00 146 0.00Igq om023 o*oo t 82 0'00297 0'00346 000298 hi 01s. Glycocoll per mol. of cuso4. 89.5 844 63'5 60.6 54'4 46'5 40.0 33'3 Rise of Freezing Point. 0'02 I" 0.0355" 0'0555" 0'0393" 0'072" 0.0885" 0.0643" 0055" Values of i for CIISOJ. 1.89 1-81 1'7.5 1-70 I *76 I '63 1'59 1 '64 Means ... ... Value of x when i for Complex Salt has same Value as for CuSO4. 3'2 3'1 3'3 3'0 2'9 2'9 3'0 2.8 3'0 i for Complex Salt is taken as 2.3'3 3'3 3'5 3'3 3'2 3'3 3'4 3'2 3'3 The values of i for solutions of CuSO, have been previously determined, but it was deemed advisable to re-determine these cryoscopically for the present purpose, so as to ensure a high degree of comparability in the measurements. The values given in the above table have been obtained by graphical interpolation and extrapolation from the following measurements- TABLE VI. Concentration of CuS04 i n xnols. per 100 grnms. OF Water. 0.003 I 0.0067 0.0109 0.0 I 94 0'022'1 0.0264 Lowering of Freezing Point. 0'09j" 0'172~ 0'247" 0'523" 0'407" 0'457" Value of i. 1.62 1-38 1.14 1.09 1-07 1'22COMPLEX COPPER-GLYCOCOLL SULPHATES 195 The values of x in columns 5 and 6 of Table V. do not differ to any very considerable extent.The true mean will lie undoubtedly between 3.0 and 3'3. It will be observed that this number is considerably lower than 3-72, the mean of the values obtained from the electrometric measurements recorded above. This divergence admits, however, of explanation, when we consider that for the solutions used for the cryoscopic measurements the ratio of mols. glycocoll to mols. CuSO, varied from 33 to 89, whilst in the case of the solutions employed in the electromotive force measurements, this ratio varied from IOO to 200. I t is to be expected that in the former case the non- electrolytic dissociation of the complex ion or ions would be greater owing to the smaller excess of glycocoll present. In accordance with this explana- tion, it will be seen that the values of i given in column 5 of Table V.show a general tendency to decrease with decreasing values of the ratio mentioned above. 3. FURTHER ELECTROMETRIC MEASUREMENTS. In order to obtain a more direct comparison between the results of the electroinetric and cryoscopic measurements, pairs of solutions were taken in which the molar ratios of glycocoll to copper sulphate were 30 and 90. In other respects the same procedure was followed as described under the final measurements of Section I of this paper. The results obtained are given in the following table- TABLE VI 1 .-E.M.F. Neaszmvnenfs in Solutions diluter with respect to Glycocoll. Concentratior in both Solutions. of cuso, 1t - 80 I t - 80 I t I60 I60 Iz Concentration of Glycocoll in 1st Solution. 3 2 8 - 312 8 - 3't I 6 3 2 16 2nd Solution.92 8 9 8 w 16 - - 9 2 I 6 E.M.F. of Combination. 0.0458 0.047 I 0.0390 0.042 2 Temp. 14" I I" I 2 O 14" Mean totals ... ... Value of x from Equation (3). 3-38 3'51 2-90 3.12 I I Equation (4). 3'15 3'30 2-75 2'95 3'23 j 3-04 The mean value of x calculated from these E.M.F. measurements agrees very well with the mean value obtained from the freezing-point measure- ments, which shows that the explanation of the previously noted divergence given at the end of Section 2 is probably the correct one. 4. CONDUCTIVITY MEASUREMENTS. In order to throw further light on the complex formations, measurements It was of the electrical conductivity of the solutions were carried out.A PHYSICO-CHEMICAL STUDY OF THE expected that on continued addition of glycocoll to copper sulphate solutions a fall of conductivity would be observed, owing partly to the formation of slower moving complex kations and partly to the increased viscosity of the solution, although these effects might be to some sinall extent counter- balanced by an increased ionisation of the complex sulphate.As will be seen, the results obtained are extremely interesting, though they cannot be explained in the manner just indicated. The glycocoll (Kahlbaum's) was re-crystallised twice from ordinary distilled water and once from conductivity water ( R = 2 x 1 0 ~ ) . The specific conductivity of an 2 solution of this purified glycocoll was 6 x ro4 (temperature, 25O). I t was found that the conductivity of a pure glycocoll solution rises rather rapidly when kept in a conductivity vessel in the presence of the electrodes.This effect is probably due to oxidation a t the surface of the platinised electrode. It is interesting to note that it does not occur when CuSO, is present, so that the complex formation appears to protect the glycocoll from oxidation. The results obtained are given in the following table- The copper sulphate used had been re-crystallised three times. I 0 TABLE VII1.-Conductivity of Glycocoll-Copper Sulplade Solutions at 25O. it1 olar Concentration of CuSO, = ; Resistance Capacity of Vessel = 0.3658. Resistance (ohms). 210'12 172.56 179'42 168'44 16 5.5 j 166.18 168.33 171.13 167.25 Specific Conductivity of Solution (reciprocal ohms per ctiitimetre cube). 174.7 x 10-5 203'7 x 10-5 211'7 x 10-5 217'0 x 10-5 220.7 x 10- 219.9 x 10- 218.5 x 10- 217.1 x 10.- 213-5 x IO- Mols. Glycocoll per mol.CuSOJ. 0 I 3 5 I 0 20 30 40 50 The specific conductivities given in column 2 have been corrected for the specific conductivity of the water (2 x IO-~). The curve given in Fig. I shows clearly the relationship between con- ductivity and number of mols. glycocoll. present in the solution. In the case of CuSO, and ZnSO,, the ordinates in the diagram run from 174-7 to 222.7. Contrary to expectation, the first effect of the addition of glycocoll is to increase the conductivity of the solution ; thus on the addition of I mol. glycocoll the conductivity rises by no less an amount than 16.6 per cent. On the addition of 10 mols. glycocoll per mol. CuSO, the conductivity attains a maximum (increase of 26.3 per cent.), after which further addition of glycocoll produces a gradual decrease of conductivity.The sharp initial rise of conductivity is very marked. In order to see how far this behaviour is to be accounted for by complex formation, the effect of glycocoll on the con- ductivity of a ZnSO, solution was studied. The result of these measurements are contained in the following table-COMPLEX COPPER-GLYCOCOLL SULPHATES 197 TABLE 1X.-Conductivities of Glycocoll-Zinc Sulplaate Solutions at 25'. Molar Concentration of ZnSO, = ?- ; Resistance Capacity of Vessel = 0.4226. 80 Resistance (ohms). 245'40 244'55 242'89 239.82 236.84 233'30 231.95 228.66 231.36 232'58 Specific Conductivity of Solution. 172'0 x 10-5 172.6 x 10-5 173.8 x 10-5 176.0 x 10-5 178.2 x 10-5 180.9 x 10-5 181-5 x 10-5 182.0 x 10-5 184.6 x 10-5 182.5 x 10-5 Mols.Glycocoll per Mol. ZnS04. 0 I 3 I 0 20 30 40 50 60 The zinc sulphate-glycocoll curve, Fig. I , also shows a maximum, but the Thus on the addition effect is not nearly so marked as in the case of CuSO,. Specific Conductivity. Specific Conductivity. 6 12 i18 24 30 36 42 48 54 60 66 Mols. Glycocoll per Mol. CuSO,, ZnSO,, or 2KCI. of I mol. glycocoll to the &SO, solution the increase of conductivity is only 0.35 per cent, whilst the maximum increase is only 7.3 pcr cent. With these results may be contrasted the effect of glycocoll on the conductivity of a KCI solution, as shown in the following table-19s APHYSICO-CHEMICAL STUDY OF THE TABLE X.-Coizductivitics of Glycocoll-KCl Solutioizs a t 25".Molar Coltcert- tration o j KCl = 12 - Resistnrtce Capaciiy = 0'4005. 40 ' Resistance. 106.30 106. j 3 I o6@3 107.66 19-94 I t 1-74 T 13.80 14'37 19-38 Sp. Conductivity of Solution. 376.52 X 10-5 375.70 X 10-5 374'12 X 10-5 371.76 x 10-5 365-91 x 10-5 364.04 x 10- 358.18 x 10-3 351'68 x 10-5 376.27 x 10-5 Mols. Glycocoll per Double Mol. KCI. 0 I 3 5 I 0 20 30 40 50 As will be seen from the curve in Fig. I, the effect of glycocoll is to diminish the conductivity of the KC1-solution by an amount proportional to the concentration of the glycocoll. In the diagram the ordinates for KCJ run from 332.52 to $30'52. This diminution is probably due to the increased viscosity of the solution, and is a well-known effect of non-electro- lytes.This effect will also be present in the cases of CuSO, and ZnSO,, but thcxe is evidently also present some other cause which tends to iizcrease the conductivity, the maxima observed being due to the conflicting action of these two causes. Now both ZnSO, and CuSO, are perceptibly hydrolysed in aqueous solution. We may represent the hydrolytic equilibrium by the equation- CuSO, + 2 H,O(Cu (OH), + H,SO, or by- Cu .* + 2 H,O + Cu (OH), + 2 He. Evidently, since glycocoll, being an amphoteric substance, can act both 3s acid and base, it will disturb this equilibrium. It will tend to remove Cu(OH), by the formation of the copper salt of glycocoll, and it may be also supposed to tend to remove He ions by the formation of glycocoll sulphate. The case of ZnSO, is similar.Now it is known:;: that the copper salt of glycoccll is a peculiar salt, which, though the salt of a very weak acid, is preserved from much hydrolysis by an '' internal " complex formation. Hence there may be a considerable formation of this salt from the Cu(OH), and the glycocoll, whilst, owing to the fact that glycocoll is a very weak base, there will be only a very small degree of neutralisation of the free acid. The result is that addition of glycocoll to a CuSO, solution will increase the hydrolysis, producing an increase of H-ions, and hence a considerable increase of conductivity. Somewhat similar considerations will apply to ZnSO,, though in this case, owing to a very much smaller tendency to form complexes, the effect will be much smaller.It is not pretended that these remarks give a comprehensive analysis of this very interesting equilibrium, though they probably suffice to indicate qualitatively the nature of the reactions occurring. It is necessary, however, to prove that the addition of glycocoll actually does increase the H. concentration. Experiments bearing on the point are described in the next section. * Ley, Zcif.~clzr*iff~f. Elekimclzeni., 10, S) j4, 1904.COMPLEX COPPER-GLYCOCOLL SULPHATES 199 Time (minutes). 5. EFFECT OF GLYCOCOLL ON THE H'CONCENTRATION OF AQUEOUS SOLUTIOXS OF CuSO, AND ZNSO,. In order to test whether addition of glycocoll increased the H. concen- tration of a ZuSO, solution, the E.M.F. of the cell 6 CuSO4,5 per cent. Sugar. s C u S O 4 , g Glycocoll, 5 per cent, Sugar.I I f was measured at 17" and found to be 0.005~ volt (current in cell in direction indicated by arrow). The palladium electrodes were charged electrolytically to just visible gas-evolution in dilute H2S0,, then washed, and left short- circuited in dilute (&) HC1 overnight. They were found to show a small difference of potential when measured against each other in 12 HC1. This has been deducted in the above result. The E.M.F. of the above cell shows that the addition of glycocoll produces an appreciable increase in the H* concentration. If we neg- lect the small liquid potential, and calculate by means of the formula C ~ = o ~ o o o 1 9 8 T L o g ~ , we find 1-23 as a roughly approximate value for the c2 ratio of increase of the €3. concentration. This method cannot be applied'to the copper solutioiis owing to precipitation of metallic copper by the palladium-hydrogen electrode, so in this case comparative measurements on the rate of inversion of cane sugar were made. The solutions used were 5 per cent.with respect to recrystallised cane sugar. The polarimeter readings are given in the following table. 200 Temperature 60*so C. TABLE XI .-Iizversion of Carte Sugar by Copper-glycocoll Solutions. I I 0 70 66 '47 148 2 16 215 179" 413/ 179" 42' 179" 34l 1 79" 30' These results, though not pretending to great accuracy, are sufficient to show that the presence of the glycocoll has very appreciably increased the H. concentration of the CuSO, solution. 6. PRODUCTS OF ISOTHERMAL CRYSTALLISATION OF AQUEOUS SOLUTIONS CONTAINING CuSO, AND GLYCOCOLL.Solutions containing CuSO, and glycocoll were allowed to crystallise at room temperature over calcium chloride or concentrated sulphuric acid. The crops of crystals so obtained were drained on the filter pump, dried on porous plates, and then microsocopically examined and analysed. Copper was determined electrolytically or as Cu,S. Glycocoll was calculated from200 A PHYSICO-CHEMICAL STUDY OF THE the percentage of nitrogen found on combustion. Water was determined from the loss of weight on heating to 1 1 0 ~ - 1 2 0 ~ in vucuo, the substance being contained in a weighed glass tube connected with a gas washing flask containing concentrated sulphuric acid. SO, was determined gravi- metrically in the usual way. Exjminteizt I.-TWO solutions were made up, each from 12 grms..glycocoll, 5 grms. CuSO, . jH,O, and 75 C.C. water. The first crop of dark blue crystals from each solution was analysed. Crystals from Solution ( I ) . Crystals from Solution ( 2 ) . !- Copper ... 10.6 per cent. I 1037 per cent. H,O . . . . . . 4.8 I ,, , , j 3-41 ) * ,, Glycocoll ... 65-84 ,, ,, (by difference) 68.81 ,, ,, SO, . . . . . . 18.75 ,, ,, 18-01 ,, 7 , , For the crop of crystals from Solution ( I ) we have Mols* glycOcO1l- Mols. Cu -5'3' There is more SO, present than would, for the given copper content, correspond to CuSO, or any complex copper-glycocoll sulphate of the formula Cu(G),SO,. The amount of water of crystallisation in the crystals from the second solution corresponds pretty closely to I mol.water per mol. copper. If we calculate, taking the figures in the first column, from the Cu percentage the percentages of glycocoll and SO, corresponding to the formula Cu(4G) SO,. H,O, we get 50 and 16 respectively. The excesses over these, namely, 15-84 and 2-75, are in the molar ratio 1-84: I . Assuming these crystal crops to be chiefly heterogeneous mixtures of two phases, it seems possible, therefore, that they might coiisist chiefly of Cu(4G)S04 . H,O and (NH,-CH, . COOH),H,SO, (but see later). Ex$erimenf 2.-Solution made up from 18 grms. glycocoll and 10 grms. CuS0,5H,O in IOO C.C. water. The first crop of crystals was dried and extracted with ether in a Soxhlet apparatus. The weight of the substance before extraction was 2.2888 grms., after extraction 2'2700 grms.We may conclude therefore that it contains little, if any, free glycocoll. Analysis of extracted crystals- Copper . . . . . . . . . . . . 25'23 per cent. Glycocoll . . . . . . . . . . . . 68.29 ,, ,, so, . . . . . . . . . . . . . . . 3-04 ,, ), H,O {by difference) ... - a * 4'44 ,, 9 , The result of crystallising from a solution relatively richer in CuSO, (in comparison with glycocoll) is to more than double the copper percentage, whilst the percentage of SO, is reduced to one-ninth of its former value. I t is evident that this crop of crystals consists mainly of a compound of copper and glycocoll (see discussion of results of Experiment 3). Experiment 3.-Original solution the same as in Experiment 2. Successive crops of crystals were obtained, examined, and analysed.The crystals were not extracted with ether. First Crop.-It consisted of dark blue nodular clumps of crystals.COMPLEX COPPER-GLYCOCOLL SULPHATES 301 Analysis.-Copper . . . . . . 27-99 per cent. Glycocoll . . . . . . 61.88 ,, ,, (by difference) so4 . . . . . . 2‘34 ,, ,, Water . . . . . . 7‘79 ,> J , Sccoizd Crop.--In appearance siiiiilar to first crop. Analysis.-Copper . . . . . . 24’95 per cent. . . . . . . so4 3-19 9 1 J l Other constituents not determined. Third Crop.-Evidently heterogeneous. It coiisisted of dark blue needles mixed with almost colourless crystals. Analysis.-Copper . . . . . . 9-46 per cent. Glycocoll ... 66-65 ,, ,, SO4 . . . . . . 19‘93 ,, 9 , Water . . . . . . 2-26 ,, ,, Fozrrth Croj,.-Fairly large colourless crystals, with a sniall amount of dark blue lumpy solid.The colourless crystals were free from copper and contained 30.68 per cent. H,S04 (calculated from amount of SO, found). Fifrh Crop.-Consisted of a mass of dark blue silky needles, with here and there a small dark blue lumpy nodule. The blue needles contained 28-47 per cent. Cu. During the course of this work a solution containing glycocoll and CuSO,, which had been set aside to crystallise, became accidentally con- taminated with HC1. From this solution large very pale blue (monoclinic or triclinic) crystals were deposited. On analysis they yielded the following results- Glycocoll . . . . . . . . . . . . 69-57 per cent. . . . . . . . . . . . . 30.23 ,, .. Copper . . . . . . . . . . . . 0.10 . . . . Water . .. . . . . . . . . . 0.09 7, 7, Neglecting the copper and water found, these crystals consist to 99-56 per cent, of a sulphate of glycocoll of the composition, glycocoll=6~)*66 per cent., H,SO,=30’34 per cent., which corresponds with the known, so-called ‘I basic,” glycocoll sulphate, whose formula is (NHZ . CH, . CO,H),H,SO, (glycocoll=6y87 per cent., H2S0,=30*r3 per cent.). These crystals cor- responded closely in appearance with the colourless crystals observed i n the third and fourth crops (Experiment 3 ) , and from the percentage of H,SO, (30.68) found by analysis in the colourless crystals of the fourth crop, there can be little doubt that these colourless crystals were the “basic” glycocoll sulphate. The dark blue needles observed in the fifth crop were separated 3s far as possible from the rest by means of a mixture of methylene iodide and benzol.In appearaiice they closely resembled the well-known copper salt of glycocoll, Cu (NHZ. CH, . CO,), . H,O and con- tained 28-47 per cent. Cu, whilst copper glycocoll contains 27.7 per cent. Cu. Judging from the microscopical examination, there was now very strong presumption that the third crop consisted chiefly of copper glycocoll and There can be little doubt that these two substances are identical.202 A PHYSICO-CHEMICAL STUDY OF THE " basic " glycocoll sulphate. following figures :- This view is confirmed on examining the I. 11. Copper . . . . . . . . . . . . . . . 9-46 ... 9-46 Glycocoll . . . . . . . . . . . . 67.93 ... 68.73 H,SO, 20'35 20'3 5 . . . . . . .. . . . . . . . ... Water . . . . . . . . . . . . . . . 2426 ... 2.68 Colunin I. gives the composition of the crop as found by analysis. Now, 9.46 parts Cu as copper glycocoll correspond to 22-01 parts glycocoll and to 2.68 parts water, whilst 20.35 parts H,SO, as (NH, . CH, . COOH),H,SO, correspond to 46.72 parts glycocoll. Therefore, had the crop consisted of copper glycocoll and basic glycocoll sulphate, it would have had the com- position indicated in Column II., which agrees sufficiently closely with that given in Column 1. It is impossible to say from the experimental results what are the exact constituents of the first crop of crystals obtained in Experiment 3. It appears possible that they consisted of copper glycocoll admixed with a basic complex copper glycocoll sulphate, but as there is not sufficient other evidence to support such a conclusion, it is scarcely worth while to reproduce here the arithmetical details of the numerous calculations made.In conclusion, it may be stated that the crystals from Solution 2 (Experi- ment I ) might be looked upon as mainly a mixture of copper glycocoll and the basic glycocoll sulphate, for on analysis the conglomerate yielded 12-84 per cent. N, whilst had it consisted of the substances mentioned, a simple calculation from the other analytical data shows that it would have contained 12-44 per cent. N. 7. COSCLUSIONS. The crystallisation experiments described in Section 6 confirm the con- clusions arrived at in Sections 4 and 5 of this paper, namely, that the effect of the first addition of glycocoll to a solution of CuSO, is to disturb the hydrolytic equilibrium by the formation of undissociated copper glycocoll, with the consequent increase of free H,SO,.The maximum increase in the specific conductivity 2 CuSO,, produced by the addition of 10 mols. glycocoll per mol. CuSO,, was 26.3 per cent. If this CuSO, solution be regarded (to a first approximation) as completely ionised, then, since the ionic conductivities of 2H. and Cu- are about 2 x 347 and 80 respectively, the replacement of Cu.. by 2H' would increase the specific conductivity by 2 j6 per cent. The actually observed increase would correspond, therefore, to a conversion of only about 10 per cent. of the CuSO, present in the 80 solution into copper glycocoll and free sulphuric acid (which at this dilution would combine with very little glycocoll). It is clear, therefore, that this initial action is soon brought to a stop by the increasing H* concentration (which throws back the CU(OH)~ concentration), and that after this the further addition of glycocoll results mainly in the formation of complex copper glycocoll kations.This second action, therefore, constitutes the niain effect i n solutions which contain large excesses of glycocoll relatively to CuSO,. The conclusions arrived at in Sections I, 2, and 3 remain, therefore, practically undisturbed. The freezing-point measurements alone are s u 6 - 80COMPLEX COPPER-GLYCOCOLL SULPHATES 203 cient to show that in solutions rich in glycocoll the main actions occurring cannot be represented by the equation- CuSO, + z(NH, .CH, CO,H) = Cu(C0,. CH, . NH,), + H,SO, CuSO, + 4(NH,. CH,. CO,H) = Cu(C0,. CH, . NH,), + (NH, . CH, CO,H), . H,SO, ; or- for if so, the addition of I mol. of CuSO, to strong solutions of glycocoll' would involve a decided increase in the number of " osmotically active " units in the solution, whereas there was always observed a decrease. Moreover, the quantitative agreement between the results calculated from the E.M.F. and freezing-point measurements is strong evidence in favour of the theoretical basis on which these results were calculated. It must be confessed, however, that more work requires to be done before this complicated equilibrium is thoroughly cleared up. In the complex copper glycocoll sulphates the glycocoll molecules are doubtless related to the copper atom in the same manner as the ammonia molecules in the complex copper ammonia sulphates. In both cases the highest katic1ii.c compiex appears to contain 4 molecules per I atom of copper, and it seeins most probable that the glycocoll or ammonia molecules are related to the copper atom through the '' subordinate " valencies of the nitrogen atom. The case of copper glycocoll itself has been investigated by Bruni and Fornara : and by Ley.+ It appears probable that the constitution of this salt must be represented by the formula- 0 . CO . CH,. NH, ........ .... ._.. CU..: I .............. ...... .......... .... I ...... .... 0. CO .CH,. NH, where the secondary or lines. The deep colour resist the conclusion that exhibit is subordinate valencies are indicated by the dotted of all these salts is very striking. It is difficult t o the powerful selective light absorption which they intimately connected with the interplay of these secondary or subordinate affinities, and that this phenomenon is a very general one. The only way i n which one can a t present represent the constitution of the complex sulphate Cu(4G)S04 is therefore (in analogy with the above) as follows- NH, . CH,. COOH .................... COOH. CH,. NH, ...... CU-so, ........... ,,(..' '.._. COOH . CH,. NH,' NH,.CH,. COOH in which there exist secondary affinity relationships between the copper and nitrogen atoms. In conclusion, I have great pleasure in expressing my best thanks to Professor Donnan for his kind advice and assistance during the course of this work. LIVERPOOL, November 18, 1907: * G. Rruni and Fornara, Rend ti. K. Accnd. d. Liiicci, Roma, xiii. gal 26. t Zeitschr$t filr Elcktrochemie, 10, 954, 1904.