THE FOLDING OF A FILTER PAPER
If a filter paper is folded along its diameter, and again folded along the radius at right angles to the original fold, a cone is formed on opening, the angle of which is 60°. Funnels for analytical use are supposed to have the same angle, but are rarely accurate. It is possible, however, with care, to fit a filter thus folded into a funnel in such a way as to prevent air from passing down between the paper and the funnel to break the column of liquid in the stem, which aids greatly, by its gentle suction, in promoting the rate of filtration.
Such a filter has, however, the disadvantage that there are three thicknesses of paper back of half of its filtering surface, as a consequence of which one half of a precipitate washes or drains more slowly. Much time may be saved in the aggregate by learning to fold a filter in such a way as to improve its effective filtering surface. The directions which follow, though apparently complicated on first reading, are easily applied and easily remembered. Use a 6-inch filter for practice. Place four dots on the filter, two each on diameters which are at right angles to each other. Then proceed as follows: (1) Fold the filter evenly across one of the diameters, creasing it carefully; (2) open the paper, turn it over, rotate it 90° to the right, bring the edges together and crease along the other diameter; (3) open, and rotate 45° to the right, bring edges together, and crease evenly; (4) open, and rotate 90° to the right, and crease evenly; (5) open, turn the filter over, rotate 22-(1/2)° to the right, and crease evenly; (6) open, rotate 45° to the right and crease evenly; (7) open, rotate 45° to the right and crease evenly; (8) open, rotate 45° to the right and crease evenly; (9) open the filter, and, starting with one of the dots between thumb and forefinger of the right hand, fold the second crease to the left over on it, and do the same with each of the other dots. Place it, thus folded, in the funnel, moisten it, and fit to the side of the funnel. The filter will then have four short segments where there are three thicknesses and four where there is one thickness, but the latter are evenly distributed around its circumference, thus greatly aiding the passage of liquids through the paper and hastening both filtration and washing of the whole contents of the filter.
!SAMPLE PAGES FOR LABORATORY RECORDS!
!Page A!
Date
CALIBRATION OF BURETTE No.
___________________________________________________________________________
| | | |
BURETTE | DIFFERENCE | OBSERVED | DIFFERENCE | CALCULATED
READINGS | | WEIGHTS | | CORRECTION
_______________|______________|______________|______________|______________
0.02 | | 16.27 | |
10.12 | 10.10 | 26.35 | 10.08 | -.02
20.09 | 9.97 | 36.26 | 9.91 | -.06
30.16 | 10.07 | 46.34 | 10.08 | +.01
40.19 | 10.03 | 56.31 | 9.97 | -.06
50.00 | 9.81 | 66.17 | 9.86 | +.05
_______________|______________|______________|______________|______________
These data to be obtained in duplicate for each burette.
!Page B!
Date
DETERMINATION OF COMPARATIVE STRENGTH HCl vs. NaOH
___________________________________________________________________________
| |
DETERMINATION | I | II
_________________________|________________________|________________________
| |
| Corrected | Corrected
Final Reading HCl | 48.17 48.08 | 43.20 43.14
Initial Reading HCl | 0.12 .12 | .17 .17
| ——- ——- | ——- ——-
| 47.96 | 42.97
| |
| Corrected | Corrected
Final Reading HCl | 46.36 46.29 | 40.51 40.37
Initial Reading HCl | 1.75 1.75 | .50 .50
| ——- ——- | ——- ——-
| 44.54 | 39.87
| |
log cc. NaOH | 1.6468 | 1.6008
colog cc. HCl | 8.3192 | 8.3668
| ——— | ———
| 9.9680 - 10 | 9.9676 - 10
1 cc. HCl | .9290 cc. NaOH | .9282 cc. NaOH
Mean | .9286 |
_________________________|________________________|________________________
Signed
!Page C!
Date
STANDARDIZATION OF HYDROCHLORIC ACID
=====================================================================
| |
Weight sample and tube| 9.1793 | 8.1731
| 8.1731 | 6.9187
| ——— | ———
Weight sample | 1.0062 | 1.2544
| |
Final Reading HCl | 39.97 39.83 | 49.90 49.77
Initial Reading HCl | .00 .00 | .04 .04
| ——- ——- | ——- ——-
| 39.83 | 49.73
| |
Final Reading NaOH | .26 .26 | .67 .67
Initial Reading NaOH | .12 .12 | .36 .36
| —- —- | —- —-
| .14 | .31
| |
| .14 | .31
Corrected cc. HCl | 39.83 - ——- = 39.68 | 49.73 - ——- = 49.40
| .9286 | .9286
| |
log sample | 0.0025 | 0.0983
colog cc | 8.4014 - 10 | 8.3063 - 10
colog milli equivalent| 1.2757 | 1.2757
| ——— | ———
| 9.6796 - 10 | 9.6803 - 10
| |
Normal value HCl | .4782 | .4789
Mean | .4786 |
| |
=====================================================================
Signed
!Page D!
Date
DETERMINATION OF CHLORINE IN CHLORIDE, SAMPLE No.
=====================================================================
| |
Weight sample and tube| 16.1721 | 15.9976
| 15.9976 | 15.7117
| ———- | ———-
Weight sample | .1745 | .2859
| |
Weight crucible | |
+ precipitate | 14.4496 | 15.6915
Constant weights | 14.4487 | 15.6915
| 14.4485 |
| |
Weight crucible | 14.2216 | 15.3196
Constant weight | 14.2216 | 15.3194
| |
Weight AgCl | .2269 | .3721
| |
log Cl | 1.5496 | 1.5496
log weight AgCl | 9.3558 - 10 | 9.5706 - 10
log 100 | 2.0000 | 2.0000
colog AgCl | 7.8438 - 10 | 7.7438 - 10
colog sample | 0.7583 | 0.5438
| ———- | ———-
| 1.5075 | 1.5078
| |
Cl in sample No. | 32.18% | 32.20%
| |
=====================================================================
Signed
STRENGTH OF REAGENTS
The concentrations given in this table are those suggested for use in the procedures described in the foregoing pages. It is obvious, however, that an exact adherence to these quantities is not essential.
Approx. Approx.
Grams relation relation
per to normal to molal
liter. solution solution
Ammonium oxalate, (NH_{4}){2}C{2}O_{4}.H_{2}O 40 0.5N 0.25
Barium chloride, BaCl_{2}.2H_{2}O 25 0.2N 0.1
Magnesium ammonium chloride (of MgCl_{2}) 71 1.5N 0.75
Mercuric chloride, HgCl_{2} 45 0.33N 0.66
Potassium hydroxide, KOH (sp. gr. 1.27) 480
Potassium thiocyanate, KSCN 5 0.05N 0.55
Silver nitrate, AgNO_{3} 21 0.125N 0.125
Sodium hydroxide, NaOH 100 2.5N 2.5
Sodium carbonate. Na_{2}CO_{3} 159 3N 1.5
Sodium phosphate, Na_{2}HPO_{4}.12H_{2}O 90 0.5N or 0.75N 0.25
Stannous chloride, SnCl_{2}, made by saturating hydrochloric acid (sp. gr. 1.2) with tin, diluting with an equal volume of water, and adding a slight excess of acid from time to time. A strip of metallic tin is kept in the bottle.
A solution of ammonium molybdate is best prepared as follows: Stir 100 grams of molybdic acid (MoO_{3}) into 400 cc. of cold, distilled water. Add 80 cc. of concentrated ammonium hydroxide (sp. gr. 0.90). Filter, and pour the filtrate slowly, with constant stirring, into a mixture of 400 cc. concentrated nitric acid (sp. gr. 1.42) and 600 cc. of water. Add to the mixture about 0.05 gram of microcosmic salt. Filter, after allowing the whole to stand for 24 hours.
The following data regarding the common acids and aqueous ammonia are based upon percentages given in the Standard Tables of the Manufacturing Chemists' Association of the United States [!J.S.C.I.!, 24 (1905), 787-790]. All gravities are taken at 15.5°C. and compared with water at the same temperature.
Aqueous ammonia (sp. gr. 0.96) contains 9.91 per cent NH_{3} by weight, and corresponds to a 5.6 N and 5.6 molal solution.
Aqueous ammonia (sp. gr. 0.90) contains 28.52 per cent NH_{3} by weight, and corresponds to a 5.6 N and 5.6 molal solution.
Hydrochloric acid (sp. gr. 1.12) contains 23.81 per cent HCl by weight, and corresponds to a 7.3 N and 7.3 molal solution.
Hydrochloric acid (sp. gr. 1.20) contains 39.80 per cent HCl by weight, and corresponds to a 13.1 N and 13.1 molal solution.
Nitric acid (sp. gr. 1.20) contains 32.25 per cent HNO_{3} by weight, and corresponds to a 6.1 N and 6.1 molal solution:
Nitric acid (sp. gr. 1.42) contains 69.96 per cent HNO_{3} by weight, and corresponds to a 15.8 N and 15.8 molal solution.
Sulphuric acid (sp. gr. 1.8354) contains 93.19 per cent H_{2}SO_{4} by weight, and corresponds to a 34.8 N or 17.4 molal solution.
Sulphuric acid (sp. gr. 1.18) contains 24.74 per cent H_{2}SO_{4} by weight, and corresponds to a 5.9 N or 2.95 molal solution.
The term !normal! (N), as used above, has the same significance as in volumetric analyses. The molal solution is assumed to contain one molecular weight in grams in a liter of solution.
DENSITIES AND VOLUMES OF WATER AT TEMPERATURES FROM 15-30°C.
Temperature Density. Volume.
Centigrade.
4° 1.000000 1.000000 15° 0.999126 1.000874 16° 0.998970 1.001031 17° 0.998801 1.001200 18° 0.998622 1.001380 19° 0.998432 1.001571 20° 0.998230 1.001773 21° 0.998019 1.001985 22° 0.997797 1.002208 23° 0.997565 1.002441 24° 0.997323 1.002685 25° 0.997071 1.002938 26° 0.996810 1.003201 27° 0.996539 1.003473 28° 0.996259 1.003755 29° 0.995971 1.004046 30° 0.995673 1.004346
Authority: Landolt, Börnstein, and Meyerhoffer's !Tabellen!, third edition.
CORRECTIONS FOR CHANGE OF TEMPERATURE OF STANDARD SOLUTIONS
The values below are average values computed from data relating to a considerable number of solutions. They are sufficiently accurate for use in chemical analyses, except in the comparatively few cases where the highest attainable accuracy is demanded in chemical investigations. The expansion coefficients should then be carefully determined for the solutions employed. For a compilation of the existing data, consult Landolt, Börnstein, and Meyerhoffer's !Tabellen!, third edition.
Corrections for 1 cc.
Concentration. of solution between
15° and 35°C.
Normal .00029
0.5 Normal .00025
0.1 Normal or more dilute solutions .00020
The volume of solution used should be multiplied by the values given, and that product multiplied by the number of degrees which the temperature of the solution varies from the standard temperature selected for the laboratory. The total correction thus found is subtracted from the observed burette reading if the temperature is higher than the standard, or added, if it is lower. Corrections are not usually necessary for variations of temperature of 2°C. or less.