272 HUGHES THE REACTION BETWEEN XXVIII .-The Reaction between Sodium Chloride Solution and Metallic Magnesium. By WILLIAM HUGHES. (>OLD aqueous solutions of various salts including sodium chloride, sodium hydrogen carbonate sodium carbonate and magnesium sulphate were found to react with magnesium powder with con-siderably more speed than one would expect since cold water acts very slowly on the metal and solutions of alkali hydroxides not a t all. That the metal slowly dissolves in solutions of its own salts with the formation of hydrogen the hydroxide or a basic salt has been observed by Kippenberger (Chem. Zeit. 1895 19 269) Vitali (L’Orosi 1895 18 289) Lemoine (Compt. rend. 1899 129 29l), Bryant (Chem. News 1899 79 75) Kahlenberg ( J . Amer. Chem. SOC.1903 25 350) and Roberts and Brown (ibid. 1903 25 801). Liberation of the metal together with hydrogen from various salt solutions by magnesium has been described by Commaille (Compt. rend. 1866 63 556) Clowes and Caven (P. 1897 13, 22l) Divers (P. 1598 14 57) Tommasi (BUZZ. SOC. chim. 1899, [iii] 21 855> and Faktor (Pharm. Post 1905 38 153). Lohnstein (Zeitsck. Elektrochem. 1907 13 612) found that the action of magnesium on acetic acid was catalysed positively by the addition of some salts and negatively by others. Knapp (Chem. News 1912 105 253) found that palladium chloride solutions and Michailenko and Mushinsky ( J . Rziss. Phys. Chem. SOC. 1912 44 181) that the water of crystallisation of certain salts were acted on by magnesium with the evolution of hydrogen.EXPERIMENTAL. I n the preliminary experiments i t was found that 0.329 gram of ordinary magnesium powder and 35-3 C.C. of 2N-sodium chloride solution gave 291.4 C.C. of a gas a t the end of a week. The metal darkened and a white gelatinous solid was disseminated through-out the liquid. The greyish-black powder slowly changed to a compact white solid but the reaction was not quite complete at the end of seven days. The theoretical yield of hydrogen is 325 C.C. a t N.T.P. One C.C. of the original sodium chloride solution and 1 C.C. of the solution which had been acted on by the magnesium gave SODIUM CHLORIDE SOLUTION AND METALLIC MAGNESIUM. 273 tit,re of 13-62 C.C. and 13.70 C.C. respectively with silver nitrate. 38.6 C.C. of the gas after absorption for fifteen minutes over freshly prepared alkaline pyrogallol measured 37.5 C.C.These results were taken to indicate that the gas was hydrogen only and it was determined to seek a relation i f any between the rate of evolution of gas and the concentration of the sodium chloride solution. The method adopted was to add known amounts of magnesium to the different solutions which had been saturated with hydrogen, and to measure the initial velocity of the reaction by reading the volume of hydrogen evolved a t 25* without shaking a t short intervals for a total period of two or three minutes. Magnesium .-A supply of ordinary magnesium powder appar-ently quite bright and free from oxide was fractionally sifted and the portion passing through between sieves of 90 and 60 meshes t o the inch respectively was used.(0.0692 gave 0.3075 Mg2P20 ; by Gibbs’s method Mg=97-03. 0.0258 gave 25.4 C.C. H [dry at 1 6 . 5 O and 726 mm.] Mg=96.45 per cent.) Only traces of aluminium and zinc could be detected in the substance. Since the phenomena investigated seemed to depend on the nature of the solutions and not on the mall amounts of impurity in the mag-nesium it was considered unnecessary to attempt any purification of this reagent. Sodium ChZoride.-Common salt was dissolved in distilled water, liltered and the solution rendered just alkaline with sodium hydr-oxide and filtered again. The slightly alkaline solution was evaporated with continual stirring and the first crop of crystals were well drained and kept over concentrated sulphuric acid.Water.-Distilled water was redistilled in a glass still which had been previously well steamed out. This water was boiled under diminished pressure previous to being used. Hydrogen.-This was prepared from zinc and pure sulphuric rtcid and purified by passing through lead nitrate solution silver nitrate solution a soda-lime tower and then a set of sodium hydr-oxide bulbs and stored over water. The number of molecules of water to each molecule of sodium chloride is repre-sented by c. A pparatus.-At first the1 solution-10 cm. deep-was contained in a test-tube and the hydrogen measured in a nitrometer the volume being read every fifteen minutes. The SoZutiong.-These were made up by weight. The rate was constant. in each case for about five hours 274 HUGHES THE .REACTION BETWEEN initial rate was read from the tangent t o the curve and reduced tQ C .C . a t N.T.P. per gram of magnesium per hour. I n the second case a conical flask was chosen as reaction vessel in order t o have a smaller hydrostatic pressure on the magnesium. It was fitted with a rubber stmopper carrying a delivery tube A (Fig. 1) drawn to a point a t the bottom of the flask for the entry of hydrogen an exit tube B which could be closed and a water manometer C behind which was fixed a millimetre scale. Selected FIG. 1. quill tubing was used in making it, and it was carefully calibrated with distilled water a t 2 5 O and found to be of uniform bore for the part calibrated namely tphe length DE. 1 crm.=0.1880 C.C.a t 2 5 O . Twice distilled water saturated with hydrogen was used in the manometler. The weighed magnesium was floated on a capsule on the solution the volume of which was always 25 c.c. and then the air displaced by and the solution saturated with hydrogen through A and B for not less than ten minutes all being immersed in the bath. The apparatus was quickly shaken and simultaneously a stop-watch was started. The volumes of hydrogen read off every half- or quarter-minute were reduced to N . T . Y . tabulated (table I) and plotted (Fig. 2 curves 1 and 2). The initial rate viras obtained by drawing the tangentt as shown. The kind of induction period a t the start is much more pronounced with the more concentrated solutions and is probably due to surf ace-tension effects chiefly in the manometer.TABLE I. c = 30. 6 minute intervals. 0 1 2 3 4 5 6 7 8 9 10 Manomo ter, A (in cm.). 0.6 0.9 1-7 2.3 2.9 3.4 3-8 4.2 4.5 5.1 4.8 Hydrogen, C.C. 0 0.15 0.55 0.55 1.15 1.40 1.60 1-80 1-95 2.10 2-25 Total pressure (corr .) 753.9 754.4 754.9 755.3 755.7 756.0 756.3 766.5 756.7 756.9 -Hydrogen, corrected. 0 0.0256 0-0941 0.1454 0.1969 0-2397 0-2742 0.3086 0.3344 0.3601 C.C. o a 6 SODIUM CHLORIDE SOLUTION AND METALLIC MAUNESIUM. 275 TABLE I. (continued). c = 38. 4 minute Nanometer Hydrogen Total intervals. A (in cm.). C.C. prossure (corr.). 0 0.36 0 1 0.78 0.21 754.0 2 1-40 0.52 754.4 3 1.98 0.81 754.9 4 2.48 1-06 755.2 FIG.2. Hydrogen, corrected. 0 0.0359 0.0889 0.1387 0-1814 C.C. The greatest precautions were taken that the solutions of sodium chloride were in each case quite free from acid. Immediately at the end of a determination they reacted alkaline. The viscosities were det'ermined with an Ostwald viscosimeter, the essential precautions being observed (Applebey T. 1910 97, 2000; from the equation density of 'solution density of w a t F time of flow of solution time of flow of water ' 17 = vwater X 276 HUGHES THE REACTION BETWEEN The densities were det,ermined with a pyknomet,er the weighings These The curves are plotted in Fig. 2, being carried out with a similarly treated counterpoise. were as shown in table 11.3 and 4. TABLE 11. Concentration. 10 20 30 35 40 50 60 e. 7725". 1.184 1.794 1.099 1.303 1.068 1.198 1.058 1-165 1.051 1-134 1.041 1.101 1.034 1.095 In t'abls I11 are given the initial rates for the diffelrent concell-trations of sodium chloride solutJons. TABLE 111. Pressure Vol. Mag-Time. Tempera- mm. hrs. min. 13 30 2 20 15 1 20 16 15 15 16 4 7 3 2 1.5 0.5 ? 9 9 9 9 9 ? 9 Y 9 3, 9 9 0.25 d-'5 0.25 Y ? 9 ) 9 9 9 9 9 , 9 9 7 9 P? ture. 19" 20 22 25 24 22.5 23 23 25 25 24-1 19.2 20 25 9 , ? ? ?? ? Y 9 7 9 , 9 9 9 9 9 9 Y ? 9 9 99 7 9 > 9 9 9 9 7 Y, ? 9 9 3 (corr. ) 762.3 763.9 766.5 758.7 758.3 766.1 767-1 768.3 749.5 749.5 749.9 749.2 749.2 749.4 749.4 750-5 752.8 752.9 753.2 754.8 752.9 752.3 767.0 753.4 753.4 753.4 753.4 754.8 754.8 754.8 754.7 755-2 750.6 C.C.(corr.) 31.32 11-99 1-87 8.32 2.29 2.42 1-58 1-87 0.72 0.18 0.45 0-51 0.37 0.0425 0.0710 0.0683 0.03845 0.0664 0.0479 0.0944 0.0684 0.0342 0.041 7 0.0135 0.0513 0.0531 0-0454 0.0343 0.041 1 0.041 1 0.0386 0.0429 0.0148 nesium , c. Gram. 9 0.0984 18 0.1069 27 0.0995 45 0-1004 35 0.0985 40 0.1004 44 0.1018 39 0.0977 30 0.1165 30 0.0333 30 0-1798 30 0.1513 30 0.1184 30 0.0840 30 0.1367 30 0.1248 10 0.1590 20 0.1531 30 0.1062 35 0.1702 40 0.1216 50 0.1507 60 0.1343 32 0.0955 34 0.1767 36 0.1940 38 0.1478 45 0.1412 55 0.1518 65 0.1581 75 0.1502 100 0.1722 0-1969 Rate.Remarks. 23.5 First method. 48-1 75.1 62.2 87.3 96.5 62.2 71-6 93.1 1 124.1 J 29.0 ' 52.1 54.2 66.6 67.5 54.4 Quarter niiriute intervals. 74.6 17.0 Metal wetted QC-cidentally during bubbling i n hydrogen. 69.7 65.7 73.6 59.5 65.0 62.4 61-6 '59.7 18-0 Water onl SODIUM CHLORIDE SOLUTION AND METALLIC MAGNESIUM. 277 These rates are plot.ted against concentrations in curve 5. The arrow indicates the rate for water ( c = 00 ) and the crosses denote the' values obtained with the nitromet'er. R e sult s . No great accuracy can be claimed for the numerical values, chiefly because1 the assumption that the total area of equal weights of the sifted magnesium is constant is only approximately true.However it is evidentl that curve 5 passes through a maximum a t r = 32 ; also the surface density of water molecules in contact with niagnesium (neglecting surface concentration effects) is given by { cp/ ( c M + M,)}+ where Mw is the molar weight of water M8 that of sodium chloride and p t.he density of the solution. Values of this expression ( =T) have been found for various concentrations a i d then plot-ted against the corresponding rates in curve 6. This passes through a maximum for a-0.1426 about or c = 3 7 . One would expect a maximum rate f o r c=m -pure water since then the magnesium surface would be apparently open to attack by a denser population of water molecules.Again the values of the viscosity hydrostatic pressure and surf ace tension (Forch Ann. l'hysik 1905 [iv] 17 744) are each greater for c = 3 2 than for weaker solutions so it seems that the maximum a t c=32 is n o t duo to any special ease of expulsion of gas through the solution. Purther the specific conductivity o€ sodium chloride solutions steadily increases to a maximum a t the saturation point so that a t c = 3 2 the1 conductivity is not' best suited for electrolytic action of impurities in the magnesium to take place. Conclusions . (1) Both alkaline and neutral salts positively catalyse the reac-tion between ordinary magnesium and purified water a t the ordinary temperature!. (2) With sodium chloride solut'ions the rate of evolution of hydrogen depends on the concentration the differences being easily detected by the eye. The init.ial rates for approximately equal areas of magnesium in cont'act with different concentrations of sodium chlolride solutions have been measured and a maximum has been found for a solution ob 32 molecules of water per molecule of sodium chloride. (3) It is considered that the existence of this maximum points to a specific effect of the dissolved sodium chloride on the water. BEDFORD MODERN SCHOOL, BEDFORD. [Received October 23rd 1918.