GRAVIMETRIC DETERMINATION.

Before the introduction of Gooch"s process it was usual to determine the boron trioxide "by difference." If the alcoholic distillate containing the boric acid is digested with about 1 gram (a known weight) of lime for ten or fifteen minutes, the alcohol can be evaporated off without danger of loss. Either calcium nitrate or acetate (which will be formed at the same time) yields lime upon subsequent ignition. Consequently, the increase in weight, after ignition, upon that of the lime taken gives the amount of boron trioxide present. The trioxide contains 31.4 per cent. of boron (B). Since magnesia does not form a soluble hydrate it cannot satisfactorily be used instead of lime.

[Ill.u.s.tration: FIG. 82.]

The apparatus required is shown in fig. 82. It consists of a small retort or evaporating vessel made out of a pipette of 200 c.c. capacity.

This is heated by means of a paraffin-bath at 130 or 140 C. It is connected with an upright condenser, at the lower end of which is a small flask which serves as a receiver.

The quant.i.ty of the borate taken should contain not more than 0.2 gram of the trioxide. Insoluble compounds are "dissolved in nitric acid at once, or, if necessary, first fused with sodium carbonate." With soluble and alkaline borates sufficient nitric acid is added to render it faintly acid. The solution is then introduced into the retort.

"The lime, to retain the boric acid in the distillate, is ignited in the crucible in which the evaporation of the distillate is to be made subsequently." It is then cooled in the desiccator for ten minutes, and weighed. The lime is transferred to the receiving flask and slaked with a little water. The retort is lowered into the bath so that "only the rear dips below the surface." The evaporation is carried to dryness, the retort being lowered further into the bath as the evaporation proceeds. Ten c.c. of methyl alcohol are introduced upon the residue, and the evaporation again started. Six such portions of alcohol are thus distilled and 2 c.c. of water are introduced and evaporated between the second and third, as also between the fourth and fifth distillations. If acetic acid is used instead of nitric in the first instance this addition of water is unnecessary.

The distillate is evaporated in the crucible ignited over the blowpipe, cooled in the desiccator for ten minutes and weighed. The increase in weight gives the boron trioxide. The results tend to be from 1 to 2 milligrams too high.

VOLUMETRIC METHOD.

This method is applicable to the indirect determination of boric acid in borax and similar compounds. It is based on the measurement of the quant.i.ty of normal solution of acid required to replace the boric acid, and, consequently, is rather a measure of the soda present. The process is an alkalimetric one, and is carried out as follows:--Weigh up 3 grams of the sample and dissolve in water. Tint with methyl orange, and run in from an ordinary burette normal solution of sulphuric acid until a pink tint is got. 100 c.c. of the normal solution of acid are equal to 7.0 grams of boron trioxide (B_{2}O_{3}), or 10.1 grams of anhydrous borax (Na_{2}B_{4}O_{7}).

~Examination of Borax.~--In addition to the determination just given, the following determinations are also required:--

~Water.~--Take about 2 grams and heat to tranquil fusion in a platinum crucible. Count the loss in weight as water.

~Sulphuric Oxide.~--Take 2 grams, dissolve in water, acidify with hydrochloric acid, filter, and precipitate with barium chloride. Wash the precipitate, ignite, and weigh as barium sulphate (see _Sulphur_).

~Chlorine.~--Take 2 grams, dissolve in water, acidify with nitric acid, filter, and add silver nitrate. Collect, wash, and weigh the precipitate as silver chloride.

~Alumina.~--Take 5 or 10 grams, dissolve in water, boil, add ammonia in slight excess, and filter off the precipitate when it has settled. Wash with hot water, ignite, and weigh as alumina (Al_{2}O_{3}).

FOOTNOTES:

[113] If the dishes show a manganese stain, wash them out with a few drops of hydrochloric and sulphurous acids. Pa.s.s the acid liquor through the same small filter but collect the liquor apart. Make ammoniacal and again pa.s.s through the filter, this time collecting the liquid with the main filtrate.

[114] This rarely amounts to more than 1 milligram.

[115] To make this, dissolve 1 gram of t.i.tanium oxide by fusing for some time with an excess of bisulphate of potash and dissolve out with cold water and sulphuric acid. Dilute to 1 litre, having previously added not less than 50 c.c. of strong sulphuric acid: 1 c.c. will contain .01 gram of TiO_{2}. For the a.s.say take 10 c.c. of this, add 2 c.c. of peroxide of hydrogen and dilute to 100 c.c. Run this from a burette into the flask until the colour equals that of the a.s.say. Each c.c. equals 1 milligram of TiO_{2}. Fluorides must be absent.

[116] C + O_{2} = CO_{2}

[117] For example, soluble organic acids formed by partial oxidation with nitric acid.

[118] For coals, and other bodies containing sulphur, chromate of lead should be used instead of oxide of copper; and the temperature should be limited to dull redness.

[119] This may be prepared by dissolving 534 grams of ammonium chloride and 854 grams of crystallized cupric chloride (CuCl_{2}.2H_{2}O) in hot water and crystallizing.

[120] Soda-lime is made by dissolving 100 grams of "soda" in water, and carefully slaking 200 grams of lime with it. Evaporate to dryness in an iron dish and ignite at a low red heat in a crucible. Use the small lumps.

[121] Made by diluting 1 part by measure of saturated lime-water up to 10 with recently boiled distilled water.

[122] See under _Gasometric a.s.says_.

[123] See "A Method for the Separation and Estimation of Boric Acid," by F.A. Gooch, _Chemical News_, January 7, 1887.

APPENDIX A.

TABLE OF ATOMIC WEIGHTS AND OTHER CONSTANTS.

---------+------------+----------+----------+--------- | | | | Symbols.| Names. | Atomic | Specific | Melting | | Weights. | Gravity. | Points.

---------+------------+----------+----------+--------- | | | | C.

Ag | Silver | 107.9 | 10.5 | 1000 Al | Aluminium | 27.0 | 2.7 | 700 As | a.r.s.enic | 75.0 | 5.9 | Au | Gold | 197.3 | 19.2 | 1200 B | Boron | 11.0 | 2.7 | Ba | Barium | 137.0 | 4.0 | Be | Beryllium | 9.0 | 2.1 | Bi | Bis.m.u.th | 208.9 | 9.8 | 270 Br | Bromine | 80.0 | 3.2 | -25 C | Carbon | 12.0 | | Ca | Calcium | 40.0 | 1.6 | Cd | Cadmium | 112.0 | 8.6 | 315 Ce | Cerium | 140.2 | 6.7 | Cl | Chlorine | 35.5 | | Co | Cobalt | 59.0 | 8.5 | Cr | Chromium | 52.1 | 7.3 | Cs | Caesium | 132.9 | 1.9 | 25 Cu | Copper | 63.4 | 8.9 | 1090 Di | Didymium | 142.3 | 6.5 | Er | Erbium | 166.3 | | F | Fluorine | 19.0 | | Fe | Iron | 56.0 | 7.8 | Ga | Gallium | 69.0 | 5.9 | 30 Ge | Germanium | 72.3 | | H | Hydrogen | 1.0 | | Hg | Mercury | 200.0 | 13.6 | -40 I | Iodine | 126.8 | 4.9 | 106 In | Indium | 113.7 | 7.4 | 175 Ir | Iridium | 193.1 | 22.4 | K | Pota.s.sium | 39.1 | 0.86 | 62.5 La | Lanthanum | 138.2 | 6.1 | Li | Lithium | 7.0 | 0.59 | 180 Mg | Magnesium | 24.3 | 1.7 | Mn | Manganese | 55.0 | 8.0 | Mo | Molybdenum | 96.0 | 8.6 | N | Nitrogen | 14.0 | | Na | Sodium | 23.0 | 0.97 | 95.6 Nb | Niobium | 94.0 | 4.1 | Ni | Nickel | 58.7 | 8.9 | O | Oxygen | 16.0 | | Os | Osmium | 191.7 | 22.4 | P | Phosphorus | 31.0 | 1.8 | 44 Pb | Lead | 206.9 | 11.4 | 334 Pd | Palladium | 106.6 | 11.4 | 1350 Pt | Platinum | 195.0 | 21.5 | 2000 Rb | Rubidium | 85.5 | 1.5 | 38.5 Rh | Rhodium | 103.5 | 12.1 | Ru | Ruthenium | 101.6 | 11.4 | S | Sulphur | 32.0 | 2.0 | 115 Sb | Antimony | 120.0 | 6.7 | 425 Se | Selenium | 79.0 | 4.8 | 100 Si | Silicon | 28.4 | 2.0 | Sn | Tin | 119.0 | 7.3 | 235 Sr | Strontium | 87.6 | 2.5 | Ta | Tantalum | 182.6 | | Te | Tellurium | 125.0 | 6.2 | 480 Th | Thorium | 232.6 | 7.8 | Ti | t.i.tanium | 48.0 | 5.3 | Tl | Thallium | 204.2 | 11.9 | 294 U | Uranium | 239.6 | 18.4 | V | Vanadium | 51.4 | 5.5 | W | Tungsten | 184.0 | 19.1 | Y | Yttrium | 89.1 | | Yb | Ytterbium | 173.0 | | Zn | Zinc | 65.3 | 6.9 | 423 Zr | Zirconium | 90.6 | 4.1 | _________|____________|__________|__________|_________

The atomic weights in this table are in accord with the numbers given by F.W. Clarke (Dec. 6, 1890), chief chemist of the United States Geological Survey.

[Ill.u.s.tration: _Table for Converting Degrees of the Centigrade Thermometer into Degrees of Fahrenheit"s Scale._]

Nitric Acid.

_Table showing the percentage, by Weight, of Real Acid_ (HNO_{3}) _in Aqueous Solutions of Nitric Acid of different Specific Gravities.

Temperature_, 15 C.

-------+-------++-------+-------++-------+------- 1.530 | 100.0 || 1.405 | 66.0 || 1.205 | 33.0 1.527 | 99.0 || 1.400 | 65.0 || 1.198 | 32.0 1.524 | 98.0 || 1.395 | 64.0 || 1.192 | 31.0 1.520 | 97.0 || 1.390 | 63.0 || 1.185 | 30.0 1.516 | 96.0 || 1.386 | 62.0 || 1.179 | 29.0 1.513 | 95.0 || 1.380 | 61.0 || 1.172 | 28.0 1.509 | 94.0 || 1.374 | 60.0 || 1.166 | 27.0 1.506 | 93.0 || 1.368 | 59.0 || 1.159 | 26.0 1.503 | 92.0 || 1.363 | 58.0 || 1.152 | 25.0 1.499 | 91.0 || 1.358 | 57.0 || 1.145 | 24.0 1.495 | 90.0 || 1.353 | 56.0 || 1.138 | 23.0 1.492 | 89.0 || 1.346 | 55.0 || 1.132 | 22.0 1.488 | 88.0 || 1.341 | 54.0 || 1.126 | 21.0 1.485 | 87.0 || 1.335 | 53.0 || 1.120 | 20.0 1.482 | 86.0 || 1.329 | 52.0 || 1.114 | 19.0 1.478 | 85.0 || 1.323 | 51.0 || 1.108 | 18.0 1.474 | 84.0 || 1.317 | 50.0 || 1.102 | 17.0 1.470 | 83.0 || 1.311 | 49.0 || 1.096 | 16.0 1.467 | 82.0 || 1.304 | 48.0 || 1.089 | 15.0 1.463 | 81.0 || 1.298 | 47.0 || 1.083 | 14.0 1.460 | 80.0 || 1.291 | 46.0 || 1.077 | 13.0 1.456 | 79.0 || 1.284 | 45.0 || 1.071 | 12.0 1.452 | 78.0 || 1.277 | 44.0 || 1.065 | 11.0 1.449 | 77.0 || 1.270 | 43.0 || 1.060 | 10.0 1.445 | 76.0 || 1.264 | 42.0 || 1.053 | 9.0 1.442 | 75.0 || 1.257 | 41.0 || 1.047 | 8.0 1.438 | 74.0 || 1.251 | 40.0 || 1.041 | 7.0 1.435 | 73.0 || 1.244 | 39.0 || 1.034 | 6.0 1.431 | 72.0 || 1.238 | 38.0 || 1.028 | 5.0 1.427 | 71.0 || 1.232 | 37.0 || 1.022 | 4.0 1.423 | 70.0 || 1.225 | 36.0 || 1.016 | 3.0 1.418 | 69.0 || 1.218 | 35.0 || 1.010 | 2.0 1.414 | 68.0 || 1.212 | 34.0 || 1.004 | 1.0 1.410 | 67.0 || | || | -------+-------++-------+-------++-------+--------

HYDROCHLORIC ACID.

_Table showing the percentage, by Weight, of Real Acid_ (HCl) _in Aqueous Solutions of Hydrochloric Acid of different Specific Gravities.

Temperature_, 15 C.

-----------+---------++----------+---------++----------+--------- | 1.2000 | 40.78 || 1.1410 | 28.54 || 1.0798 | 16.31 | | 1.1982 | 40.37 || 1.1389 | 28.13 || 1.0778 | 15.90 | | 1.1964 | 39.96 || 1.1369 | 27.72 || 1.0758 | 15.49 | | 1.1946 | 39.55 || 1.1349 | 27.32 || 1.0738 | 15.08 | | 1.1928 | 39.14 || 1.1328 | 26.91 || 1.0718 | 14.68 | | 1.1910 | 38.74 || 1.1308 | 26.50 || 1.0697 | 14.27 | | 1.1893 | 38.33 || 1.1287 | 26.10 || 1.0677 | 13.86 | | 1.1875 | 37.92 || 1.1267 | 25.69 || 1.0657 | 13.45 | | 1.1857 | 37.51 || 1.1247 | 25.28 || 1.0637 | 13.05 | | 1.1846 | 37.11 || 1.1226 | 24.87 || 1.0617 | 12.64 | | 1.1822 | 36.70 || 1.1206 | 24.46 || 1.0597 | 12.23 | | 1.1802 | 36.29 || 1.1185 | 24.06 || 1.0577 | 11.82 | | 1.1782 | 35.88 || 1.1164 | 23.65 || 1.0557 | 11.41 | | 1.1762 | 35.47 || 1.1143 | 23.24 || 1.0537 | 11.01 | | 1.1741 | 35.07 || 1.1123 | 22.83 || 1.0517 | 10.60 | | 1.1721 | 34.66 || 1.1102 | 22.43 || 1.0497 | 10.19 | | 1.1701 | 34.25 || 1.1082 | 22.02 || 1.0477 | 9.78 | | 1.1681 | 33.84 || 1.1061 | 21.61 || 1.0457 | 9.38 | | 1.1661 | 33.43 || 1.1041 | 21.20 || 1.0437 | 8.97 | | 1.1641 | 33.03 || 1.1020 | 20.79 || 1.0417 | 8.56 | | 1.1620 | 32.62 || 1.1000 | 20.39 || 1.0397 | 8.15 | | 1.1599 | 32.21 || 1.0980 | 19.98 || 1.0377 | 7.75 | | 1.1578 | 31.80 || 1.0960 | 19.57 || 1.0357 | 7.34 | | 1.1557 | 31.40 || 1.0939 | 19.16 || 1.0337 | 6.93 | | 1.1536 | 30.99 || 1.0919 | 18.76 || 1.0318 | 6.52 | | 1.1515 | 30.58 || 1.0899 | 18.35 || 1.0298 | 6.11 | | 1.1494 | 30.17 || 1.0879 | 17.94 || 1.0279 | 5.51 | | 1.1473 | 29.76 || 1.0859 | 17.53 || 1.0259 | 5.30 | | 1.1452 | 29.36 || 1.0838 | 17.12 || 1.0239 | 4.89 | | 1.1431 | 28.95 || 1.0818 | 16.72 || 1.0200 | 4.01 | -----------+---------++----------+---------++----------+---------

AMMONIA.

_Table showing the percentage, by Weight, of Real Ammonia_ (NH_{3}) _in Aqueous Solutions of Ammonia of different Specific Gravities.

Temperature_, 14 C.

----------+--------++----------+--------++----------+-------- 0.8844 | 36.0 || 0.9145 | 23.6 || 0.9534 | 11.6 0.8852 | 35.6 || 0.9156 | 23.2 || 0.9549 | 11.2 0.8860 | 35.2 || 0.9168 | 22.8 || 0.9563 | 10.8 0.8868 | 34.8 || 0.9180 | 22.4 || 0.9578 | 10.4 0.8877 | 34.4 || 0.9191 | 22.0 || 0.9593 | 10.0 0.8885 | 34.0 || 0.9203 | 21.6 || 0.9608 | 9.6 0.8894 | 33.6 || 0.9215 | 21.2 || 0.9623 | 9.2 0.8903 | 33.2 || 0.9227 | 20.8 || 0.9639 | 8.8 0.8911 | 32.8 || 0.9239 | 20.4 || 0.9654 | 8.4 0.8920 | 32.4 || 0.9251 | 20.0 || 0.9670 | 8.0 0.8929 | 32.0 || 0.9264 | 19.6 || 0.9685 | 7.6 0.8938 | 31.6 || 0.9277 | 19.2 || 0.9701 | 7.2 0.8948 | 31.2 || 0.9289 | 18.8 || 0.9717 | 6.8 0.8957 | 30.8 || 0.9302 | 18.4 || 0.9733 | 6.4 0.8967 | 30.4 || 0.9314 | 18.0 || 0.9749 | 6.0 0.8976 | 30.0 || 0.9327 | 17.6 || 0.9765 | 5.6 0.8986 | 29.6 || 0.9340 | 17.2 || 0.9781 | 5.2 0.8996 | 29.2 || 0.9353 | 16.8 || 0.9790 | 4.8 0.9006 | 28.8 || 0.9366 | 16.4 || 0.9807 | 4.6 0.9016 | 28.4 || 0.9380 | 16.0 || 0.9823 | 4.2 0.9026 | 28.0 || 0.9393 | 15.6 || 0.9839 | 3.8 0.9036 | 27.6 || 0.9407 | 15.2 || 0.9855 | 3.4 0.9047 | 27.2 || 0.9420 | 14.8 || 0.9873 | 3.0 0.9057 | 26.8 || 0.9434 | 14.4 || 0.9890 | 2.6 0.9068 | 26.4 || 0.9449 | 14.0 || 0.9907 | 2.2 0.9078 | 26.0 || 0.9463 | 13.6 || 0.9924 | 1.8 0.9089 | 25.6 || 0.9477 | 13.2 || 0.9941 | 1.4 0.9100 | 25.2 || 0.9491 | 12.8 || 0.9959 | 1.0 0.9111 | 24.8 || 0.9505 | 12.4 || 0.9975 | 0.6 0.9122 | 24.4 || 0.9520 | 12.0 || 0.9991 | 0.2 0.9133 | 24.0 || | || | ----------+--------++----------+--------++----------+--------

SULPHURIC ACID.

_Table showing the percentage, by Weight, of Real Acid_ (H_{2}SO_{4}) _in Aqueous Solutions of Sulphuric Acid of varying Specific Gravity.

Temperature_, 15 C.