388 On a Quantitative Bloicjnpe Assay of Chromium. 



simple fusion, obtained in the shape of beads, docs away with 

 the tedious processes of filtration and evaporation ; and if in a 

 few cases the results thus obtained are not quite as accurate as 

 those arrived at in the wet way, they are quite sufficiently so for 

 all practical purposes. With metals difficultly fusible and redu- 

 cible, which can not be brought into any available alloy (such 

 as, besides others, iron and chromium), we are obliged par- 

 tially at least to resort to the wet way, A mixed method of this 

 kind has been proposed by Plattner for iron ; and the one I noAV 

 propose for chromium is of a similar kind. It is primarily in- 

 tended for use in the field; also by the manufacturer to whom 

 examinations of complex residues are frequently recurring; 

 similarly it may serve to determine quickly and with considera- 

 ble accuracy the value of the commercial preparations of chro- 

 mium. In this I have not, however, invented any process es- 

 sentially new. I have only attempted to adapt to the particular 

 purpose in view, phenomena well known before, and there is 

 undoubtedly room left for a good deal of improvement as it is. 

 In describing the particular manipulations, I shall suppose the 

 reader to be acquainted with the micro-laboratory of Plattner 

 (his Uowpipe chest\ and his book on the same subject.* 



The first step, as may be supposed, is the conversion of the 

 chromium contained in the ore into chromic acid by fusion with 

 alkalies and the simultaneous action of oxydizirig agents, by t 



which process chromium is at once separated from nearly all of 

 the basic elements. In the qualitative test, this fusion is per- 

 formed in the large platinum spoon, before the blowpipe flame. 

 This process is always accompanied by mechanical loss from 

 spirting of the flux, especially when nitre is used, without which, 

 in most cases, the process is a slow and imperfect one. I found 

 that a very slight admixture of phosphate of soda lessens the 

 spirting very much ; but I could find no means of preventing it 

 altogether in an open vessel. I found it most convenient to use 

 a platinum crncible of the same size and pattern as the clay ones 

 ordinarily used ; covered by a platinum torrefaction dish put on 

 bottom downwards, and bent slightly out of shape, so as when 

 set on to leave on one side a small orifice between itself and the 

 nm of the crucible. The object of this orifice is to give exit to 

 the gases, especially when, as sometimes happens, the flux mside 

 rises so high as to reach the cover. But for this orifice (whicli 

 must be kept very hot during the fusion) the cover would in 

 such a case be lifted off by puffs, allowing the ejection of parti- 

 cles of the flux. 



mic iron ore ; but in practice its use is incouT 



The ypoonjflmp, and other apparatus referred to beyond, ; 

 ner s chest. 



/ 



