Arsenic can also be estimated by volumetric methods; for this purpose it must be in the arsenious condition, and the method of estimation consists in converting it into the arsenic condition by means of a standard solution of iodine, in the presence of a cold saturated solution of sodium bicarbonate.
In quantitative analysis the methods can be subdivided into: (a) gravimetric, in which the constituent is precipitated either as a definite insoluble compound by the addition of certain reagents, or electrolytically, by the passage of an electric current; (b) volumetric, in which the volume of a reagent of a known strength which produces a certain definite reaction is measured; (c) colorimetric, in which the solution has a particular tint, which can be compared with solutions of known strengths.
Volumetric analysis, possessing as it does many advantages over the gravimetric methods, has of late years been extensively developed.
Chlorimetry (1824), alkalimetry (1828), and the volumetric determination of silver and chlorine (1832) were worked out by Gay Lussac; but although the advantages of the method were patent, it received recognition very slowly.
And of iodine and sulphurous acid to the estimation of copper and many other substances by Robert Wilhelm Bunsen, marks an epoch in the early history of volumetric analysis.
Quantitative methods are divided into four groups, which we now pass on to consider in the following sequence: (a) gravimetric, (0) volumetric, (7) electrolytic, (5) colorimetric.
Volumetric Analysis: F.
Sutton, Systematic Handbook of Volumetric Analysis (1904); F.
These methods have been purely chemical (either gravimetric or volumetric), physical (determinations of the density of nitrogen, nitric oxide, &c.) or physicochemical.
Volumetric methods are used, but the uncertainty of the end of the reaction has led to the suggestion of special indicators, or of determining the amount of cuprous oxide gravimetrically.
Volumetric methods have also been devised.
For all pharmaceutical purposes, however, the use of the metric system alone is employed in all paragraphs relating to analysis, whether gravimetric or volumetric. For measures of capacity the Pharmacopoeia continues to use imperial measuring vessels graduated at the legal temperature of 62° F.
The new Pharmacopoeia also follows foreign practice, and employs metric measures of capacity and volumetric vessels graduated at 15.5 C., or 60° F.
Iodine has extensive applications in volumetric analysis, being used more especially for the determination of copper.
In one of them, read in 1814, he explains the principles of volumetric analysis, in which he was one of the earliest workers.
Among the volumetric methods used, the one most commonly employed is that of W.
The "dry" or fire assay for lead is largely used for the valuation of lead ores, although it is being gradually replaced by volumetric methods.
There are several volumetric methods for assaying lead ores, but the best known is that based on the precipitation of lead by ammonium molybdate in an acetic acid solution.
The most modern and the most generally accepted method is volumetric, and is based on the reaction between zinc chloride and potassium ferrocyanide, by which insoluble zinc ferrocyanide and soluble potassium chloride are formed; the presence of the slightest excess of potassium ferrocyanide is shown by a brownish tint being imparted by the solution to a drop of uranium nitrate.
It is very stable and is much used in volumetric analysis.
In general, volumetric methods are used, i.e.
The fire assay for copper ores was abandoned years ago and the electrolytic method took its place; this in turn is now largely replaced by volumetric methods.
Volumetric methods are more expeditious and require less apparatus.
The methods used in the assay for iron are volumetric, and are all based on the property possessed by certain reagents of oxidizing iron from the ferrous to the ferric state.