672 SEC. 13. - CHEMISTRY. 



2575. Filtering Apparatus, provided with a glass receiver 

 and 2 india-rubber rings and supports. 



F. A. Wolff $ Sons, Heilbronn and Vienna. 

 This filtering apparatus is intended for the use of schools. 



2456h. Cavendish's Eudiometer. E. Cctti Co. 



2575a. Model and Section of Spongy Iron Filter, 



filtering materials employed. Gustav Bischof. 



Spongy iron is metallic iron in a spongy or porous state, obtained by the 

 reduction of an oxide without fusion. The powerful property of metallic iron 

 to purify water has been known for a long time, but its application in the 

 spongy state only renders the purification sufficiently rapid to be of practical 

 iise. The water in passing through the spongy iron dissolves a minute 

 quantity of iron, which is completely retained by a mixture of sand and 

 pyrolusite underneath. 



Pyrolusite has the property of converting protosalts of iron into persists. 

 The latter are again decomposed, probably by the agency of calcic carbonate 

 in water, and the ferric hydrate formed is mechanically retained by the sand. 

 Ammonia and other substances are likewise oxidised by pyrolusite. 



The hardness of water is very considerably reduced, and every trace of 

 lead removed by filtration through the spongy iron filter. (See VI. Report 

 of the Royal Commission on Rivers Pollution, 1875, pp. 220, 221 ; Repr-rt of 

 the Registrar General, 8th January 187G ; Journal of the Royal Agricultural 

 Society of England, Vol. XI., part I., 1875, p. 158.) 



A small lateral opening in the regulator tube forms the only communi- 

 cation between the upper part of the filter and the reservoir for filtered water. 

 The flow of the water is thus completely controlled by the size of such 

 opening to ensure a sufficient contact between the purifying medium and 

 the water. 



2455a. Apparatus for showing the Decomposition of 

 Steam by the Heat of Electric Sparks. 



Prof. Frankland, F.I?.$. 



