Adeney&Shegog — Wet and Dry Methods in Chemical Analysis. 103 



slightly curved. The dimensions most convenient for the quantities 

 we dealt with were — diameter, 1 j inches ; greatest depth, 1| inches. 

 If the cavity be much larger or smaller than this, the charge cannot 

 be worked about in the proper manner. The ratio of diameter to 

 depth should be attended to, for if the hole be too deep in relation 

 to its diameter, the flame will be blown back, and the charge cannot 

 be properly heated. 



The Source of Heat. — In our earlier experiments a lamp which 

 burnt solid paraffin was used. This had the advantages of being 

 very portable and not likely to get out of order. Later on an 

 ordinary paraffin oil lamp was employed ; but, although either of 

 these lamps will answer perfectly, we found that when coal gas is 

 procurable it is by far the most convenient source of heat. It can 

 be burnt at the end of a flattened tube, and if the tube be pivoted 

 so that it can rotate in a vertical plane it will be found of advan- 

 tage in dealing with easily oxidizable metallic beads, as will be 

 explained later. 



The blowpipe used was an ordinary mouth blowpipe, furnished 

 with a platinum jet, and fixed in a clip on a retort- stand. An 

 indiarubber hand-blower was used for obtaining the blast. 



The borax used was fused in a platinum dish and powdered. 

 It should be kept in a dry and well-stoppered bottle. 



The silver was at first used in the form of nitrate, but the 

 troublesome deflagration which took place when tliis salt was 

 heated, soon led to its use being discontinued. Silver chloride, 

 mixed with the substance and borax before fusion, was next tried, 

 and was found to work very satisfactorily. Subsequently it was 

 found that with substances of a certain type, the most satisfactory 

 results were obtained when the substance and fluxes were first 

 fused together in a shallow cavity in charcoal, the oxidizing flame 

 being employed. When fusion was complete the mass was allowed 

 to cool, transferred to a cavity of the usual size and shape in a 

 fresh piece of charcoal, the silver added in the form of wire or in 

 a button, and the fusion continued in the reducing flame. Ex- 

 periments were also made in which silver oxide was used instead of 

 silver chloride, but no advantage was apparent. In some cases, 

 when dealing with metals which form infusible alloys with silver, 

 lead was added, either as litharge or as metal. The results obtained 

 were not satisfactory, but this requires further working out. 



