80 Exchanges. 
rub down the work carefully, and then coat with bleached shellac 
in alcohol. This prevents the grain of the wood from being 
raised. Then proceed with two zinc coats in turpentine, and 
finally with zinc in dammar varnish. There is an absolute neces- 
sity for using the shellac, as without it the natural sap will in time 
discolour the white surface. 
Polished Floors.—A remarkable innovation has been made— 
that of the application of soluble glass to floors, the water-glass 
being previously coloured if desired. It gives a polished, smooth, 
and handsome surface. The seams are first filled with a cement 
of water-glass and gypsum ; successive coats of water-glass, of the 
consistence of syrup, are applied with a stiff brush. A higher 
finish is given by pumicing off the last layer, and then putting on 
a coating of oil. 
Exchanges. 
d 
“Cambridge Antiquarian Proceedings,” 1879 to date, cost price, 44s. 6d. ; 
also, occasional publications. Exchange for Text-books on the Microscope, 
Entomological or Botanical Books, or Standard Works on Higher Mathematics 
or Natural Philosophy.—G. H. Bryan, Thornlea, Chaucer Road, Cambridge. 
DRAGON FLirs.—Mr. W. Harcourt Bath, Ladywood, Birmingham, desires 
to correspond with students of the Odona/a in all parts of the globe, as he is 
specially working up this group of insects. Specimens for figuring in his 
forthcoming ‘‘ Monograph of British Dragon Flies” will be very acceptable. 
There is probably no class of insects so neglected as Dragon flies, and Mr. W. 
Harcourt Bath will be very pleased to assist anyone desirous of commencing 
their study. 
The following well-mounted and neatly finished Micro Slides for exchange: 
—Cystolitus of Cactus ; Cuticle of Cactus, in C.B.3; Cuticle of Axasassa 
sativa, showing large stomata, in C.B.; Scale of the Szdak, a Russian fish ; 
Pollen of Salvia patens, in C.B.; Section of Dammar Wood, in C.B. ; Skin 
of Sterxgeon, with bony plates 27 sztz. Approval to be mutual.—Rev. H. W. 
Lett, M.A., Aghaderg Glebe, Loughbrickland, Co. Down. 
British Medical Journal, June, 1883—Dec., 1885, 5 vols., complete, 
unbound. What offers in microscopic, botanic, entomologic, or other books, 
periodicals, apparatus, or cash ?—G, H. Bryan, Thornlea, Trumpington Road, 
Cambridge. 
_ To our Readers.—The Editor will be glad if correspondents 
will send him marked newspapers or periodicals containing notices 
of Scientific Meetings and other items of interest. 
