TAXXI.-Y'he Compound H,R,O, and Its Salts

View Article Online / Journal Homepage / Table of Contents for this issue

BAY: THE COMPOUND E~R,O~AND ITS SALTS. 803 Published on 01 January 1918. Downloaded by Brown University 26/10/2014 14:32:25.

TAXXI.-Y'he Compound H,R,O, and its Salts. By RAMESCHANDRA RAY. TN a previous coinmunication (T., 1914, 105, 2162), it was shown that the so-called amorphous berm, prepared by the reduction of boron trioxicle by means of riiagiiesium, probably consisted of a sollid solution cof a lower oxide of boron, sometimes in combination with a little magnesium oxide; in elenient,ary bo'ron. If thin were View Article Online 804 RAY : THE COMPOUND H,B,O, AND ITS SALTS.

really the case, it appelared probable thab the soluble part! of the fusion would contain solme o€ the lower oxide, together with excess of boron trioxide, and the, present investigation was undertaken with a view to detect and isolate the lower oxide. The fusion obtained by heating a mixture oF boron trioxide with magnesium powder generally contains magnesium boride, amorphous boron (so-called), magnesium o'xide, partly in combination with boron trioxide, and, as will be shown later, the lower oxide or oxides of boron. If the operation is carried out under conditions which will now be described, the quantity of magnesium boride in the mixture is very small, although it cannot' be altogether eliminated. A mixture of 1 part, of magnesium powder and 3.5 parts of anhydrous boron trioxide, finely powdered and passed through a 120-mesh sieve, was heated in a covered magnesia-lined crubible, through which a current of hydrogen was passed, to a bright red heat for about three hours. After cooling in an atmosphere of hydrogen, the mass was powdered and mixed with half its weight of anhydrous boron trioxidel. The mixture was then heated again as beforel. The fused mass was powdered, water was added to it, and it was allowed to remain for from one to three days, to allow of the decomposition of traces of lriagiiesium boride. The solution was filtered, and the boric acid removed by the method employed by Travers, Ray, and Gupta (PamphZef, H. K. Lewis and Co., 1916), which consisted in shaking the solution in a vacuum for several days with precipitated magnesium hydroxide, and removing the excess a€ the latter, together with the insoluble magnesium metaborate, by filtration In analysing the solutions, advantage was also taken of the fact, discovered by

Published on 01 January 1918. Downloaded by Brown University 26/10/2014 14:32:25. Travers, Ray, and Gupta (loc. cit.), that when solutions of the rower oxides of boron are evaporated with excess of lime and the residue ignited to constant weight, oxidation does not take place and the increase in the weight of thel lime corresponds'with the weight of the lower oxide in the sulution. For the purpose of analysis, three equal quantities of the solution were treated as follolws : (a) The magnesium was precipitated in the usual manner and the result expressed as the o'xide MgO. (b) The solution was inbroduced into a platinum crucible containing lime, ignited to constant weight, and, after evaporation to dryness, the crucible was again ignited to constant weight, the increase in weight giving the weight of the magnesium oxide and of the lower oxide1 of boron, together with the weight of any trace of boric acid left in the solution, View Article Online RAY: THE COMPOUND H2B40, AND ITS SALTS. 805

(c) The third portion of the solutdon was evaporated to dryness in a vacuum and the residue heated 'in a sealed bulb with con- centrated nitric acid. The bulb became1 filled with red fumes, and the lower oxide! of boron was oxidised to boron trioxide. The bulb was then opened, the. excess of nitric acid removed by evaporation in a vacuum desiccator over solid sodium hydroxide, and thel boric acid determined by the lime method. The following are the resiilts of the experiments: I. 11. 171. 1V. V. MgO per 100 C.C. of solution...... 0.0980 0.1156 0.1248 0,0876 0-1608 Residue less MgO per 100 C.C...... 0.3048 0.3581 0.3896 0.2726 0.5012 B2O9 from residue per 100 C.C...... 0.3452 0.4036 0.4324 0.3048 0.5664 MgO in gram-mols. per 100 C.C...... 0.0024 0.0029 0.0031 0.0022 0.0040 B in gram-atoms per 100 C.C...... 0.0099 0.0115 0.0123 0.0087 0-0161 Ratio B/Mg ...... 4.1 3.9 4.1 3.9 4-0 B2O? 1.132 1.126 l-li? 1.118 1.130 (Residue less MgO ) } '. It is clear that the ratio B/Mg is very near 4, and that the mean value of the ratio B,O,/(Residue less MgQ), which is 1.124, closely approximates to the value of the ratio1 2B,Q,/B,O,, which is 1.129. The analytical results appear, therefore, to suggest that the solution contains a magnesium borite, the; formula of which may be written MgQ,B,O,. The oxide B,Oi has already been described by Travers, Ray, and Gupta (Zoc. cit.). Each of the solutions used in these experiments was obtained from the treatment of a different fxsion, and it was possible, there- forel, although hardly probable, that thel constancy of their composition might be attributable to1 the fact that the conditions in Published on 01 January 1918. Downloaded by Brown University 26/10/2014 14:32:25. each case were similar. The1 third preparation was therefore! treated with water four times, and the extracts were investigated separate'ly. The results of the analysis of the first extract have already been giveln ; those of the remaining extracts are tabulated below : 111, a. 111, b. 111, c. MgO per 100 C.C...... 0.0960 0.0616 0.0412 Residue less MgO per 100 c.c.. .. 0.2940 0.1804 0.1212 B203from residue per 100 c.c.... 0.3290 0.1996 0.1368 MgO in gram-mols...... 0.0024 0*0015 0~0010 B in gram-atoms ...... 0.0094 0.0057 0.0039 Ration B/Mg ...... 3.9 3.8 3.9 Be03 *'* ' '..*"' 1.119 1.106 1.128 (Residue less MgO) } Although the solutions became more and more dilute with each treatment of thei fusion with water, their composition remained View Article Online 806 RAY: THE COMPOUND R,’B406 AND ITS SALTS. Practically constant, leaving no room for doubt that the cmpoulld MgO,B,O, is really present in thenl. It has not been found possible to isolate the magnesium borite. The molecular weight o€ the cornponnct can be1 determined with sufficient accuracy from the freezing points of the solutions. 1:’ t,he magneeium salt were completely dissociated, the! molecular weight of the corresponding oxide could be determined from the f olr mu la h=18*5(TB/M-~1IT’/40))

where IV is the weight, in 100 C.C.of the solutim, of the oxide of boron, M its rnodecular weight, and H’’ the! weight of the magnesium oxide present. Since#,however, the compomd is probably dissociated only to the extent of about 75 per cent., the result will be about 15 per cent. too high. For the determination of the freezing points, measured quantities of the solutions, of which the analyses have already been given, were evaporatle8dto dryness in a vacuum. The residues were dis- solved in a measured quantity of water, and the freezing points were compared with the! freezing point of pure water. The following results were obtained:

I. 11. 111. IV. V. W ...... 0.3048 0.3584 0.3896 0.2726 0.5012 W’ ...... 0.0980 0.1156 0.1248 0.0876 0-1608 A ...... 0.090 0.105 0.116 0.082 0-148 M ...... 121 128 125 124 126 R’atio B,O,/MgQ ...... 1.0 0.96 1.0 1.0 1.0 The values for B/I agree sufficiently well with the theoretical value, 124, as calculated for the formula B,O,. On addition of ammonia to the solution, the magnesium is almost Published on 01 January 1918. Downloaded by Brown University 26/10/2014 14:32:25. completely precipitated as hydroxide, and if the ammoniacal solution is evaporated in a vacuum, a residue! is left which consists mainly of the oxide. As Travers, Ray, and Gupta have shown (Zoc. cit.), the oxide is very unstable and is readily oxidised to boric acid. If a solution of the) magnesium salt is treated with potassium hydroxide in equivalent proportions, and afterwards evaporated in a vacuum to’ small bulk, practically the whole of the magnesium separates as hydroxide and can be filttxed off. On further con- centration of the solution in a vacuum, t,he potassirnm salt separates as a crust which can be redissolved, and the salt purified by crystal- lisation five OY six times, and finally dried in a vacuum at 80-90a. The preparation is a difficult one3.and altogether only 2 to 3 gralns View Article Online RAY : THE COMPOUND H,B,Us AND ITS SALT'S. 807

of the substarice were finally obtained. The salt is stable in the absence of molisturs. The potassium was estimated by first dissolving the salt in water, evaporating the solution to dryness in a platinum vessel, and treat- ing the residue, repeatedly with hydrochloric acid and methyl alcohol. The potassium chloride was finally converted into sulphate. For the estimation of boric acid, the solution was saturated with carboil dioxide and boiled under a rr lux condenser in a current of pure air. The boric acid was titrated with N/20- alkali in the presence of mannitol, using phenolphthalein as indicator : I. 0.5036 gavel 0.3987 K,SO, and 0.3142 B,03. K=35-5; B = 19.6. 11. 0.2286 gave 0.1S21 K,SO, arid 0.1433 B,O,. K-35.7; B = 19.7. 111. 0.3378 gave 0.2889 K,SO, mct 0.2318 H,O,. K=35*2; €3 -= 19.8. K,R,O, requires K=3%.8;K- 30.2 pei- emit. The aiialyses are concordant, and the resiilh irl agreeriieiit wit11 tIhc values correspondiiig wiih tJie Co ula K,B,O,, which rnay therefore be accepted as correct. 'P'lie, molecular weight' of the substaucc was dr:teririinetl by tho c.ryoscopic niethcl, using 30 grains of' solveiit : 0.0435 gave A1== -0.052. M.W.=78. 0.0874 ,, 4' - 0.097. M.W. = 84. The value of' the molecular weight c;alculatcd I'or I1rt.1 formula JC,BaiO, is 218, and if the compound were corrlplett?ly tlissociat,ecl in solution, the1 apparent molecular weight would be 73. The con- centrations of the two solutions correspond with 1 gram-equivalent Published on 01 January 1918. Downloaded by Brown University 26/10/2014 14:32:25. in 100 and 50 litres respectively, and if the salt is ionised to the same extent as similar potassium salts, the degree of ionisation in the Lwwo solutions will be approximately 0.9 and 0.9. Without going further into the1 matter, it is obvious that, within the limits of experimental error, the result proves that the substance in solution has the formula K,E,O,, and not ths formula I!B,O,, which would dissociate into two ions and give an apparent molecular weight of approximately 50. The existence of the anhydrous salt, K2B406,of the acid H2B,0, is of interest, as it goes to confirm the views put forward by Travers, Ray, and Gupta (Zoc. cit.) as to the constitution of the borohydrates containing four atoms of boron. If the boron atoms in these conipounds are liiiked in a single chain, the oxide, B,O,, View Article Online 808 SYANBRIDW : THE HY DICATEESAND

which call be obtained by heating them, must be given ths formula Bo:Bo*Bo: yo, and the corresponding acid the formula I-__ - 0-- BO (OH) :BO *B0: €3 0(OH). The results do not offer any positive evidence that the so+called amorphous boron is a solid solution of the oxide B,O, in elementary boron, particularly as Travers, Ray, and Gupta have found indica- tions of the! existence of the oxide B,O, which is quite insoluble in water, and may bel tha oxide that is present in the solid solution. The research has, however, led to the discovery of a new series of compounds, the acid, H,B,O,, and its salts, and the results serve to extend our knowledge of the more complex compounds of boron.

In comlusiotn, I desire to thank Dr. M. W. Travers, F.R.S., at whose suggestion the research was undertaken, for the valuable help which I have always received from him.

CHEMICAL LABORATORY, PATNACOLLEGE, BANKIPORE, INDIA. [Beceived, August 13th, 1918.1 Published on 01 January 1918. Downloaded by Brown University 26/10/2014 14:32:25.