Page:Transactions of the Natural History Society of Northumberland, Durham, and Newcastle-upon-Tyne 1838 Vol.2.djvu/458

 == No. XXIII. — Upon the Employment of C HROMATE OF L EAD in the Analysis of organic Bodies. By T HOMAS R ICHARDSON .==

R EAD O CTOBER 16, 1837.
T HE Chromate of Lead may be prepared by mixing salts of lead and bichromate of potash together; the precipitated salt must then be perfectly 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 analysed 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 combustion 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 advantageous in the combustion of those bodies which have a large proportion 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.