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It must be remembered that the determination of small quantities of substances generally involves the use of reagents which are often contaminated, as an impurity, with the body sought for. Thus, in assaying silver, the oxide of lead or metallic lead used is rarely free from silver; and in the case of arsenic, the acids, zinc or ferric chloride are sure to contain arsenic. The same observation applies to the precipitation of lead by zinc, &c. The errors caused by these impurities are more marked in the determination of material having small quantities of metal than in that of ores which contain larger quantities. Errors of this kind are counteracted or neutralised by "blank" or "blind" determinations. These consist in carrying out by the side of and during the assay a duplicate experiment with the reagents only, which are thereby subjected to the same processes of solution, evaporation, filtration, &c. The final result thus obtained is deducted from that given by the assay, the difference gives the corrected result. In some cases, where it is desired or necessary to have a tangible residue or precipitate, some _pure_ inert material is added.

Yet it shows no gay foliage, nor "shade above shade a woody theatre," such as is seen on a mountain declivity. It is a simple shadowy walk--shadowy to richness, cool, tranquil, redolent of freshness. There the soul feels "private, inactive, calm, contemplative," linked to things that were and are not. The mellow hue of time, not yet stricken by decay, clothes the buildings of this college, which, compared with other edifices more steeped in maturity of years, occupies, as it were, a middle term in existence.

• Nicholas Bredimus
• Nicholas Bredimus
• Nicholas Bredimus
• Nicholas Bredimus
• Nicholas Bredimus

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