by Weight and by Volume. 209 



bismuth. When bismuth is in solution as nitrate, it may be 

 expressed thus : — 



2Bi03, NO^ X KO, 2Cr03= (2Bi03 CrO^) x KO, NO^ x NO^ 



The chromate of bismuth is of a rich yellow colour. In 

 warm solutions it is deposited almost instantly. On the addition 

 of one or two drops of bichromate only, the precipitate diffuses 

 itself throughout the mixture, imparting a yellow milkiness to 

 the whole fluid. Further addition of the bichrome test causes 

 the aggregation of the precipitate ; and on the experiment ap- 

 proaching completion, it coagulates speedily, leaving the super- 

 natant liquor perfectly free from any floating particles, in this 

 way affording facility for observing the effect of continued addition 

 of the bichrome test. At the conclusion of the experiment, 

 chromate of bismuth will cease to precipitate, and any further 

 addition of bichrome test will remain in solution, and may be 

 detected by its characteristic colour. An experiment such aa 

 just described will occupy about ten minutes. 



The preceding remarks on the estimation of bismuth apply to 

 colourless solutions only, and for such the method is specially 

 adapted. In commercial analysis, however, it is desirable to 

 analyse ores, alloys, &c. with great rapidity, approximate results 

 only being required. A simple modification of the preceding 

 method enables us to extend the volumetric mode of analysis to 

 solutions of any degree of colour. A perfectly saturated solution 

 of nitrate of bismuth (or a salt of lead), as near neutral as pos- 

 sible, is prepared, and small portions of the fluid dotted over a 

 white porcelain slab. An alloy or other specimen in solution to 

 be tested is treated in precisely the same manner as when testing 

 a colourless liquid with a standard solution of bichromate of pot- 

 ash. The standard test-licpor, in analyses such as I now refer 

 to, may be prepared of a much greater density than those pre- 

 viously described. AVhen the experiment approaches completion, 

 which may be readily ascertained even in coloured liquids by 

 the precipitate produced, the fine point of a glass rod is inserted 

 after each addition, and the moistened rod brought into contact 

 with one of the dots of a solution of bismuth on the white slab. 

 As soon as an excess of bichromate of potash remains in solution, 

 on touching a dot of bismuth solution with the wet rod a film 

 of chromate of bismuth will instantly form. So long as any 

 bismuth remains in solution, the bismuth dots will remain per- 

 fectly clear; consequently the formation of a yellow milkiness in 

 the bismuth dots replaces the colour of bichromate of potash 

 itself as an indicator of the progress of the experiment. 



The only source of error in the mass analyses originates in 

 the circumstance of one or more drops of the bichrome test being 



