412 Mr. Richardson on the Employment of Chromate of Lead. 



No. XXIII. — Upon the Employment of Chromate of Lead in the Analysis 

 of organic Bodies. By Thomas Richardson. 



Read October 16, 1837. 



The Chromate of Lead may be prepared by mixing salts of lead and 

 bichromate of potash together ; the precipitated salt must then be perfect- 

 ly well washed and dried. The dried salt is then to be carefully fused in a 

 clay crucible till it melts. The melted salt, after pounding, is ready for 

 analysis. When well melted it does not absorb so much moisture as it 

 would otherwise do, and in this case it possesses a great advantage over 

 oxide of copper. Before employing the pounded salt, it is only necessary 

 to dry it in a warm place. The mixture with the organic body to be ana- 

 lysed is made in precisely the same way as with oxide of copper, only that 

 it should be as intimate as possible, since a larger portion of substance in 

 proportion becomes exposed to the action of the fire in the same time as 

 with oxide of copper. The length of the tube necessary for the combus- 

 tion is about 25 centimetres long, and from 10 to 11 decimetres diameter. 

 It is almost unnecessary to add, that the combustion must be very slowly 

 conducted. With this salt a much larger quantity of substance can be 

 analysed than with oxide of copper, arising from its great specific gravity. 

 During the whole of the analysis a quantity of oxygen gas is disengaged 

 from the potash apparatus, which arises from the great predisposition of 

 the Chromate of Lead, to be converted into basic salt. This fact, with 

 the great quantity of oxygen which the salt contains, renders it very ad- 

 vantageous in the combustion of those bodies which have a large propor- 

 tion of carbon, and which are difficult to consume. It is also an excellent 

 means of analysing bodies containing, chlorine, bromine, &c. ; the chloride, 

 bromide, &c, of lead not being volatile. 



For the suggestion of the employment of this body in organic analysis 

 we are indebted to Prof. Liebig. 



