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Precautions in Testing Acids

It of a sample under inspection, add cautiously is essential to success, in testing acetic or from a weighed quantity of powdered pure other acids by saturation, to hit the exact dry bicarbonate of potassa, sufficient to probicarbonate of potassa, sufficient to propoint of neutralization. It will be found greatly duce exact neutralization; carefully re-weigh to simplify matters to tint with litmus (see No. the bicarbonate unconsumed. Double the 78) either the sample under examination, or loss in grains will indicate the percentage of the test liquid; but when litmus is used, it is acid in the liquid tested. advisable to apply a gentle heat to the test 76. Ure's Test of the strength of Acettube when saturation appears nearly reached; ic Acid. Ure's test gives very accurate rethe heat will expel from the liquor the free sults, if the ammonia employed is of the carbonic acid, which itself has the property proper specific gravity. To 100 grains of a of reddening litmus. A glass or wooden rod sample, very slightly reddened with neutral ACIDIMETRY. (blue) tincture of litmus, add liquor of am- | the percentage of the acid? The equivalent monia of specific gravity .992 from an acidime- of dry sulphuric acid is 40 (see No. 81); ter (see No. 82) until perfect neutralization is therefore by the rule of proportion, since effected, indicated by the original blue color 100: 40:60:24, the sample contains 24 per of the litmus being restored. The number of cent. of dry sulphuric acid. acidimetric divisions of ammonia expended, In this method the choice of the re-agent multiplied by 51 (for dry) or by 60 (for glacial) must depend on the operator. Some prefer and the product divided by 100, will give, re- the ammonia test (see No. 76), which is very spectively, the percentage of dry or glacial convenient and easily applied; others give a acid in the sample. Thus:-if a sample of preference to bicarbonates or carbonates of poof povinegar takes 10 acidimetric divisions of am- tassa or soda. Whichever be adopted, it must , it must monia to neutralize it, then 10 multiplied by be perfectly pure. A test solution, once caresolution, once care- 51, and divided by 100, gives 5.10, equivalent fully prepared of the proper strength, may be , may be to 5 per cent. of dry acid:-or, 10 multi- kept unharmed for any length of time in a plied by 60 and divided by 100, gives 6 per cent. of glacial or hydrated acid in the sample.

77. Ure's Test, by Grains, of the strength of Acetic Acid. The same strength of ammonia is to be used in the acidimeter as in the preceding test, and the number of grain-measures of ammonia employed for a multiplier instead of acidimetric divisions. The only difference is, that the product in each case must be divided by 1000 instead of 100, to give the percentage of acid.

Acidimetry.

The estimation of the quantity of an acid contained in any given sample.

The methods used are founded chiefly on the capacity of acids to saturate or neutralize alkaline bases; and, in some of the liquid acids, on specific gravity. stoppered bottle, and will be always ready for application.