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preface to fifteenth edition

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11.72 SECTION 11<br />

TABLE 11.25<br />

Tolerances for Analytical Weights (Continued)<br />

Denomination<br />

Individual<br />

<strong>to</strong>lerance,<br />

mg<br />

Class M<br />

Group<br />

<strong>to</strong>lerance,<br />

mg<br />

Individual<br />

<strong>to</strong>lerance,<br />

mg<br />

Class S<br />

Group<br />

<strong>to</strong>lerance,<br />

mg<br />

Class S-1,<br />

individual<br />

<strong>to</strong>lerance,<br />

mg<br />

Class P,<br />

individual<br />

<strong>to</strong>lerance,<br />

mg<br />

10 mg0.0054 0.014 0.030 0.060<br />

5 mg0.0054 0.014 0.028 0.055<br />

3 mg0.0054 0.0105 0.014 0.034 0.026 0.052<br />

2 mg0.0054 0.014 0.025 0.050<br />

1 mg0.0054 0.014 0.025 0.050<br />

1<br />

⁄2 mg 0.0054 0.014 0.025 ...........<br />

TABLE 11.26<br />

HeatingTemperatures, Composition of WeighingForms, and Gravimetric Fac<strong>to</strong>rs<br />

The minimum temperature required for heatinga pure precipitate <strong>to</strong> constant weight is frequently lower than<br />

that commonly recommended in gravimetric procedures. However, the higher temperature is very often still <strong>to</strong><br />

be preferred in order <strong>to</strong> ensure that contaminatingsubstances are expelled. The thermal stability ranges of various<br />

precipitates as deduced from thermograms are also tabulated. Where a stronger ignition is advisable, the safe<br />

upper limit can be ascertained.<br />

Gravimetric fac<strong>to</strong>rs are based on the 1993 International A<strong>to</strong>mic Weights. The fac<strong>to</strong>r Ag: 0.7526 given in the<br />

first line of the table indicates that the weight of precipitate obtained (AgCl) is <strong>to</strong> be multiplied by 0.7526 <strong>to</strong><br />

calculate the correspondingweight of silver.<br />

Element<br />

Thermal stability<br />

range, C<br />

Final heating<br />

temperature, C<br />

Composition of<br />

weighing form<br />

Gravimetric fac<strong>to</strong>rs<br />

Ag 70–600 130–150 AgCl Ag: 0.7526<br />

Al 475 1200 Al 2 O 3 Al: 0.5293<br />

743 743 AlPO 4 Al: 0.2212; Al 2 O 3 : 0.4180<br />

102–220 110 Al(C 9 H 6 NO) 3 Al: 0.0587; Al 2 O 3 : 0.1110<br />

As 200–275 105–110 Al 2 S 3 As: 0.6090; As 2 O 3 : 0.8041<br />

850 Mg 2 As 2 O 7 As: 0.4827; As 2 O 3 : 0.6373<br />

vacuum at 25 MgNH 4 AsO 4 ·6H 2 O As: 0.2589<br />

Au 20–957 1060 Au<br />

Ba 780–1100 780 BaSO 4 Ba: 0.5884; BaO: 0.6570<br />

60 60 BaCrO 4 Ba: 0.5421; BaO: 0.6053<br />

Be 900 1000 BeO Be: 0.3603<br />

Bi 100 BiOCl Bi: 0.8024; Bi 2 O 3 : 0.8946<br />

100 Bi(C 12 H 10 NOS) 3 Bi: 0.2387<br />

379–961 800 BiPO 4 Bi: 0.6875; Bi 2 O 3 : 0.7665<br />

Br 70–946 130–150 AgBr Br: 0.4256<br />

Ca 478–635 475–525 CaCO 3 Ca: 0.4004; CaO: 0.5601<br />

838–1025 950–1000 CaO Ca: 0.7147<br />

air-dried Ca(picrolonate) 2 ·8H 2 O Ca: 0.05642<br />

Cd 320 CdSO 4 Cd: 0.5392; CdO: 0.6159<br />

125 Cd(C 10 H 6 NO 2 ) 2 Cd: 0.2462<br />

218–420 CdS Cd: 0.7781; CdO: 0.8888<br />

Ce 360 500–600 CeO 2 Ce: 0.8141<br />

Cl 70–600 130–150 AgCl Cl: 0.2474

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