FIRTH AND MYERS: SOME I’ROPERTIES OF SOLUTIONS. ETC. 2887CCLXX.-Xome Pmpey&ies of Solutions of the B o ~ i cAcids in AZcohol. A Modz$cd Boiling-poii2 tAppayatus.By JAMES BRIERLEY FIRTH and JAMES ECKERSLEY MYERS.THE well-known property of orthoboric acid of imparting a greencolour to the alcohol Rame has usually been ascribed, a t any ratein text-books, t o the formation of some organic derivative of boricacid such as triethyl borate.This idea seems to present considerable theoretical difficulties,and i t was with the object of obtaining information on this point,and mom particularly of examining the physical properties ofalcoholic solutions of the boric acids, that the present work wasundertaken.The first part of the investigation as described in the presentcommunicati‘on is devoted t o the determination of the boilingpoints of the solutions and of the composition of the variousdistillates.Preliminary experiments indicated that it was extremely prob-able that the additions of very small proportions of orthoboric acidproduced a very slight lowering of the boiling point of ethylalcohol.This lowering appeared t o be of a similar magnitude t othat observed by the addition of small quantities of water toalcohol. It was therefore essential that the materials used shouldbe as free from water as possible, and that the experiments shouldbe carried out with the exclusion of water-vapour from the atmo-sphere.The alcohd was therefore purified, and then dried thoroughly bytreatment with metallic calcium or with lime prepared by calciningmarble.Both methods were used, and as there appeared t o be no differ-ence in the results obtained, alcohol dried over calcium wasemployed for the experiments described below.It may be men-tioned in passing that in addition to the usual precautions observe2888 FIRTH AND MYERS: SOME PROPERTIES OFin drying alcohol, the hydrocarbons sometimes found in the alcoholafter treatment with calcium were readily and completely removedby distillation from animal charcoal.The orthoboric acid was purified by several recrystallisationsfrom water; the metaboric acid was prepared by heating the ortho-acid to about 130° until decomposition was complete, and the borontrioxide was obtained by 'fusing the ortho-acid. I n the last caseP I G .1.UAthe glass was ground to a fine powderin an agate mortar. Precautionswere taken to exclude moisture fromthe meta-acid and the anhydride.The three materials were found byanalysis to be tolerably pure.As it was a question of measuringvery small differences in boilingpoint, several kinds of apparatuswere tried, and the one describedbelow was eventually used, owing tothe unsuitability of the existingtypes.The general characteristics of theapparatus, which can be thoroughlyrecommended for this kind of work,will be clear from the sketch (Fig. 1).The ordinary Beckmann boiling-point tube is used, and is enclosedin a Dewar vessel. All exposedglass surfaces are covered with alayer of cotton-lint so as t o shieldthe heated liquid and vapour fromdraughts.This precautlion is foundto be very necessary. The heatingis by an electric current of from2.5 t o 3.0 amperes, and is keptsteady by means of a rheostat withan ammeter in the circuit.The current is carried by stout platinum wires, sealed throughgIass tubes, in contact with the leads by means of mercury, untili t reaches the liquid. The wire is now very much thinner, and iscarried through a glass coil made of tubing about 2 mni. indiameter and open a t both ends, so that the wire is in contactwith the liquid. The glass coil is broken half-way along its length,so that it is really t,wo small coils with a gap ( A ) between them.The two arO bound together with platinum wire for conveniencSOLUTIONS O F THE BORIC ACIDS IN ALCOHOL.2889of handling and suspending. The gap between the coils shouldbe about 4 mm. The efficiency of the apparatus is largely dueto this gap. As the wire becomes heated the liquid inside thenarrow tube expands, and rushes out, and is replaced by otherliquid, thus causing circulation. This process goes on until boilingpoint is reached inside the coil, when the circulation becomes morerapid until the whole liquid is at the boiling point and streamsof bubbles issue from the various openings in the tube. It willbe seen that the enclosure of the wire prevents local superheatingcommon with a bare' wire, and the openings in the coil cause rapidand continuous circulation and ebullition.'rt is essential that bubbles should appear from the middle andlower opcmirlgs in the coil.It happens on rare occasions thatbubbles issue from the top and middle openings, and then super-hezting often takes place. I n such cases a slight tap will startbubbling from all three points.With a pure liquid the boiling point, as registered by a Beck-mann thermometer, remains steady to 0 ' 0 1 O or even t o 0.005°, solong as the barometric pressure remains steady.I n all experiments a control apparatus was employed containingpure alcohol, so that variations in the boiling point due to baro-metric changes could be determined and the boiling point of thesolution corrected. I n the values given below this correction hasbeen included, and all temperatures are expressed in degrees centi-grade of an arbitrary Beckmanii scale.TABLE I.Solute, H,BO,,.Solute, HBO,. Solute, B,O,.v- \ 7- ,--B. p. B. p. B. p.Gram- of Change Gram- of Change Gram- of Changemols. solu- in mols. solu- in mols. solu- inH,,BO,,. tion. b. p. HBO,. tion. b. p. B,O,. tion. b. p.A\O.OC33 1.49' -0-07' 0.0036 1-52" -0.04' 0.0049 1.52' -0.04'0.0084 1.44 -0.12 0.0074 1.48 -0.08 0.0111 1.36 -0.200.0136 1.42 -0.14 0.0140 1.43 -0.13 0.0180 1.36 -0.200.0180 1.41 -0.15 0.0200 1.41 -0.15 0.0277 1.38 -0.180.0227 1.40 -0.16 0.0261 1.40 -0.16 0.0348 1.46 -0.100.0270 1.40 -0.16 0.0311 1.40 -0.16 0.0435 1.61 +0*050.0320 1.42 -0.14 0.0375 1.41 -0.15 0.0639 1.98 +0*420.0384 1.45 -bll 0.0457 1.43 -0-13 0.0773 2-25 +0*690.0438 1.49 -0.07 0.0520 1.51 -0.05 - - -0.0500 1.52 -0.04.0.0610 1-66 - - - -0.0548 1.57 +0.01 0.0690 1.61 +0*05 - - -0.0628 1.67 +0*11 0.0800 1.69 3-0-13 - - -0,0675 1.75 +Om19 0.1334 2.30 +0*70 - - -0.0740 1.83 +Om27 0.1482 2.62 +1.06 - - -Boiling point of pure, alcohol 1.56O; volume of alcohol 75 C.C.It will be clear from the table' that there is a 'lowering of the- - - - 0.0840 1.97 f0.41 2890 FIRTH AND MYERS SOilIE PROPERTIES OF'boiling point of alcohol on adding either of the three solutes. Thislowering reaches a maximum in the case of orthoboric acid when0.0227 grain-molecule lics been added, and then amounts to 0.16' ;in the case of metaboric acid it' is 0 . 1 6 O for 0.0261 gram-molecule,and for the anhydride it is 0*20° for 0.018 gram-molecule.Thevalues given in the table are shown on the graph (Fig. 2) for thesake of comparison.No further bend or change in the curve was observed up to thepoint of saturation at boiling point.The question of the composition of the distillate was nextFIG. 2. Frc. 3.examined. The method of distilling is shown in the sketch ofthe apparatus.When sufficient time had been allowed for the solute to dissolvecompletely and the boiling point had become steady, two fractionsof the distillate each of 5 C.C. were, analysed. The distillate wastreated with water, and thus in all cases orthoboric acid wasformed, which was titrated with alkali in the presence, of glycerol.The1 assumption was made that the distillat,e contained, before theaddition of wat?r, the original solute.I n this connexion it may beremarked that it was frequently observed that after distillatioSOLUTlONS OF THE BORIC ACIDS IN ALCOHOL. 2891a small quantity of solid substance appeared in the tubes, etc., ofthe apparatus after the alcohol had evaporated. This was assumedto be the original solute.The following table gives the results obtained, the strength ofeach distillate being expremed in values of the particular soluteemployed.A separate experiment was carried out for each strength ofsolution, not as in the case of the boiling points, where the experi-rneiits in each series were inade continuous by adding successiveamounts of the solute.TABLE 11.Original volume of alcohol, 75 C.C.H,BO,. HRO,. R,O,.A h *Weight Weight i; Weight Weight i; Weight Weight in 'of 1st 2nd of 1st 2nd of 1st 2ndH,,BO, +A HBO, -7' B,O,added.fraction. added. fraction. added. fraction.0.25300.48600.63480.81701.19501.37001-58802.06002.72003-56300,03550.05940.08200-09030.10330.11150.12570.12760-14510.15800-03220-05420.07090.087 10.10250.10710.11990.12700.14120.15530.3300 0.0498 0-0435 0.5230 0.0527 0.04880.6430 0.0691 0.0673 0.9355 0.0823 0.07350.9810 0.0906 0.0892 1.2770 0.0898 0.08761.4510 0.1172 0.1103 1.8020 0.1055 0.10392.3890 0.1341 0.1305 2.3730 0.1183 0.11603-2830 0.1387 0.1400 3.1140 0.1314 0-1289- - - - - -These values are shown in the graph (Fig. 3) for comparison, allweights being expressed in grams of solute per C.C.of solution. I nthe curve for orthoboric acid the dotted line shows the coursewhich it is considered the curve should take as no reasons can beassigned for the values producing the break. They are probablydue to' experimental error.On considering the two sets of curves, the first f o r the change inboiling point and the second for the volatility of the solutes, itwill be noticed that the maximum effect on the boiling point isproduced by t,he solute of minimum volatility, boron trioxide andvice versa with orthoboric acid. I n both cases the metaboric acidoccupies a middle position in a general way.Experiments are a t present in progress t o examine whether theeffect of the solute on the vapour pressure is dependent on thetemperature, by means of surf ace-tension measurements andmeasurements of the heats of solution are being made.The conclusions drawn from the work described above are asfollow 2892 WILSON, HEILBRON, AND SUTHERLAN D : CONTRIBUTIONS(1) With certain small concentrations of orthoboric and meta-boric acids and boron trioxide, ths boiling points of ethyl alcoholsolutions are lower than the boiling point of the pure solvent.(2) Tho maximum lowering of the boiling point is produced byth3 least volatile solute, which also has the greatest subsequenteffect on the boiling point.(3) The distillate contains the original solute.n f E UWEWWY,MAKCHES~TR