208 Mr. R. W. Pearson on the Determination of Bismuth 



TT 1 ^. ... rCadmium 3'765 srs. 



In a solution containing . . . ^Bismuth 1-244!.. 



I obtained, taking the cadmium by fCadmium 3-76517 grs. 



difference ^Bismuth 1-24383 ... 



The bismuth was estimated by volume. 



Estimation of Bismuth by Volume. 



The mode of procedure in estimating bismuth by volume 

 analysis is exactly the same as in the now common methods of 

 volumetric determinations. A graduated solution of bichromate 

 of potash is added to a colourless solution of bismuth until the 

 metallic oxide in solution is converted into insoluble chromate 

 of bismuth. By observing the effect of continued addition of 

 the bichromate salt^ it is easy to note the rise of a deep yellow 

 colour in the supernatant liquid. This indicates an excess of 

 bichromate of potash, and of course the saturation of the liquid. 



Preparation of standard solutions. — Bichromate of potash, the 

 agent to be employed, as met with in commerce, is usually con- 

 taminated with sulphate of potash and chloride of potassium. 

 The removal of these and other impurities may be effected by 

 repeated crystallization of the bichromate salt. 



7-135 grains of pure crystallized bichromate of potash are weighed 

 off and dissolved in 1000 grains of water in a large graduated test 

 mixer or other convenient vessel. To avoid subsequent repetition, 

 I shall call this solution the " bichrome test," and to distinguish 

 from similar ones affix the letter A — bichrome test A. A second 

 solution, one-tenth the strength of bichrome test A, is prepared 

 in like manner. '7135 grain of bichromate of potash dissolved in 

 1000 grains of water will furnish a solution of such a strength ; 

 I call this solution the "bichrome test B." A " bichrome test C," 

 one-tenth strength of solution B, is prepared by dissolving '07135 

 grain of bichromate in 1000 grains of water. These solutions, 

 A, B, and C, will contain chromic acid in 100 grains; equal in 

 solution A to 1 grain of metallic bismuth, in solution B to 0*1 

 grain of bismuth, and in solution C chromic acid equal to '01 

 grain of bismuth. On the' correctness of these solutions of 

 course depends the value of any results that may be obtained by 

 their use. 



In my own experiments I make use of a white glass flask 

 capable of holding about 2000 grains of liquid. As it is neces- 

 sary to keep the solution hot during the experiment, I use a 

 clasp of iron plate with wooden handles; the flask having a 

 rim, it can be slipt round the neck at pleasure. 



It may be as well to notice the decomposition which takes 

 place on the addition of bichromate of potash to a solution of 



