1847.] Examination of some Atmospheric Dust. 195 



the details can judge at a glance if they have been correctly and care- 

 fully performed. This is necessarily mentioned because I could only 

 sacrifice such exceedingly minute assays, and have thus been obliged to 

 refrain from further researches, as for example its specific gravity, the 

 proportion of animal to mineral matter, and the hygrometric qualities of 

 the dust, all of which, with many other points, it would be very satisfac- 

 tory to know. I am in hopes however that I shall receive a report, with 

 specimens, u#der the Admiralty order to II. M. Ships on the Eastern 

 Station to report on Storms, in which other Meteorological phenomena 

 are I presume included. 



The dust is an olive grey powder, cohering much together, like the 

 scrapings from a paper filter, and when viewed with the magnifier is 

 evidently mixed with something like hairs of two kinds, black and ra- 

 ther thick white ones. Under the microscope it is evidently a congeries 

 of very short transparent white, black and brown hairs or fibres, with 

 some reddish, strait spines, and grains of pellucid quartz-like sand 

 adhering amongst them. There was one small grain like a seed, but 

 hard, which when viewed carefully appeared to be an earthy concretion. 

 I unfortunately lost it and could not thus try it at the blowpipe. 



It just frits' under the nail on glass, and rubbed between two glass 

 surfaces scratches them but very faintly, felting into a smooth mass from 

 the quantity of fibre. I think the taste is slightly saline, but in the very 

 minute quantity taken cannot be sure. Moistened on turmeric paper 

 it distinctly reddens it and is thus alkaline, and contains probably the 

 sub-carbonate of soda, the commonest of the alkaline salts. 



Blowpipe Examination, 



On platinum foil : held over the lamp it flames up, the fibres are 

 burnt with a strong ammoniacal odour, and a grey coherent powder, like 

 pumice, remains. 



2. On platinum foil alone : before the blowpipe; this powder fused 

 in the reducing flame but at one point only* and not at the detached 

 portions. The fused part is a bottle-green glass, and when detached is 

 found to have made a little circular hole in the platinum, undoubtedly 

 from an alkali contained in the assay. 



* Probably at one of the minute concretions noted ab'>ve, arid- which are not 

 remarked by the naked eye. 



2 d 2 



