QUANTITATIVE RESULTS OF VOLUMETRIC ANALYSIS-A GRAPHIC PROCEDURE'
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W. I. TRETSVEN Chicago, Illinois
MUCH
OF the tedious work of quantitative analysis may be eliminated by utilizing a simple one-line or twoline graph. The graphic procedure is based on the relative strengths of the reagents and has been adapted to various analyses. Since it was developed and used extensively in the laboratory for determining the salt content of chqese, it will be illustrated in terms of this application.
OFFICIAL METHOD
Briefly; in the official method "Volhard" ( I ) , a standard silver nitrate solution is added, in excess, to the weighed sample of cheese. After digestion with potassium permanganate and nitric acid to oxidize the organic matter, the excess of silver nitrate is titrated with standard thiocyanate solution using ferric alum as the indicator. The weight of sample and the strength of silver nitrate solution suffice to provide an excess. The essential reactions are:
+
+ +
NaCl AgNOs Ft AgCl N~NOI AgNOa + NHICNS AgCNS NHINOX Fe+++ +Red Color* NHICNS
+
~h~ nitwte and thiocyanate solutions mustbe standardized using a chloride, usually sodium chloride, as the ultimate standard. ordinarily this is done in terns of normality factorswhich are then employed in makine the necessarv calculations. , In tGe m a ~ h i cprocedure, sodium chloride is used as the ultimjie gtnndnrd an before, but the st
