552 Chronicles of Science. [Oct., 



To obtain these objects, the dust should be washed in a bowl, and 

 all the lightest particles allowed to float away; the remainder consists 

 of fragmentary, crystalline, and ferruginous substances ; mixed with 

 these are the polished balls described, which, under the microscope 

 by a brilliant reflected light, look like little gems. To separate the 

 spherical bodies from the irregular ones, it is only necessary to 

 sprinkle some of this material on an inclined glass plate, and by 

 gentle vibration the balls roll down, and can thus be collected. 

 Mr. Dancer considers the transparent spheres to be silicates of 

 soda or potash ; the opaque white are most likely silicate of soda or 

 potash, combined with lime and alumina; the yellow and brown 

 are silicates coloured by iron in different proportions. The black 

 globes are not all alike in composition ; some of them are silicates 

 coloured by carbon, others are iron balls coated externally with a sili- 

 cate. Many of these rusty cannon balls are probably ferrous oxide, 

 formed by the action of heat on the iron pyrites in the coal. There 

 are also balls of black magnetic oxide ; the perforated shells are pro- 

 bably ferrous sulphides. The globular form of these bodies suggests 

 that they have been thrown off in scintillations, such as are seen 

 during the combustion of iron in oxygen gas, and whilst in a fluid 

 state they assume a spheroidal form. They are carried by the 

 draught into the flue, and being of greater specific gravity than the 

 carbonaceous matter forming the smoke, they fall before the current 

 of air has reached the chimney. Some of the dust has been a con- 

 siderable time in the flue, exposed to the intensely heated circulating 

 flame ; the reducing action of this would probably convert some of 

 the oxide into metallic iron. Many of these balls have the appear- 

 ance of reduced oxides. The movements of these objects, caused by 

 the approach of a magnet under the stage of the microscope, are 

 somewhat amusing, and it is at times startling to see the crystalline 

 objects, both spherical and irregular, exhibit magnetic attraction. 



That indefatigable experimentalist, M. Schonbein, has just made 

 a further discovery respecting ozone. He finds that ordinary 

 oxygen is without action upon the protoxide of thallium, while 

 ozonized oxygen combines rapidly with this oxide, so as to form the 

 peroxide of thallium, which is brown. Paper steeped in a solution 

 of oxide of thallium and exposed to free ah, would be an excellent 

 ozonometric paper, if the carbonic acid of the air did not transform 

 the oxide into carbonate, which passes more slowly to the state of 

 peroxide, and blackens with difficulty under circumstances where 

 strips of paper, iodized and starched, become coloured at the end of 

 a few minutes in an atmosphere which contains a l-2,000,000th 

 part of ozone. The comparison between the two papers has at least 

 the advantage of proving that the coloration of the iodized paper is 

 really produced by the atmospheric ozone, and not altogether -by 

 nitrogen compounds, as believed by many. 



