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.
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.
(a) Gravimetric. - This method is made up of four operations: (I) a weighed quantity of the substance is dissolved in a suitable solvent; (2) a particular reagent is added which precipitates the substance it is desired to estimate; (3) the precipitate is filtered, washed and dried; (4) the filter paper containing the precipitate is weighed either as a tared filter, or incinerated and ignited either in air or in any other gas, and then weighed.
Standard solutions are prepared by weighing out the exact amount of the pure substance and dissolving it in water, or by forming a solution of approximate normality, determining its exact strength by gravimetric or other means, and then correcting it for any divergence.
These methods have been purely chemical (either gravimetric or volumetric), physical (determinations of the density of nitrogen, nitric oxide, &c.) or physicochemical.
Guye has given a critical discussion of the relative accuracy of the gravimetric and physico-chemical methods, and favours the latter, giving for the atomic weight a value less than 14.01.
8 and 9, in a curve showing the relation between p and D the gravimetric density, which is the specific gravity of the P lb of powder when filling the volume C, cub.
-70.75 80 Gravimetric Density Of Products Of Explosion Fig.
In., while the gravimetric volume changes from v-ZAv to v+Z p v, a change of volume of 27.73 Ov cub.
Pressure In A Closed Vessel Observed And Calculated Gravimetric Volume Fig 9.
Charge: weight 13 lb 4 oz.; gravimetric density 55.01/0.504; nature, cordite, size 30.
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 most accurate method for the determination of lead in ores is the gravimetric method, in which it is weighed as lead sulphate after the various impurities have been separated.