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.
[Illustration: 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 quantity 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 quantity 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. Pass the acid liquor through the same small filter but collect the liquor apart. Make ammoniacal and again pass 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 titanium 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 assay 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 assay. 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 Assays_.
[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 Arsenic 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 Bismuth 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 Potassium 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 Titanium 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.
[Illustration: _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.