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POPULAR SCIENCE REVIEW. 
as low a price as fourpence per pair, and hooks and eyes at one penny per 
pound. They manage these things better in France, where electro-plating is 
regulated by law, the manufacturer being required to weigh each article 
when ready for plating, in the presence of a comptroller appointed by the 
Government, aDd to report the same article for weighing again when the 
plating has been done. Electro-gilding does not appear to be a costly process ; 
a silver thimble may be handsomely coated, so as to have the appearance of 
being all gold, for threepence. Among the recipes for cleaning silver we find 
no mention of an excellent method in use for freshening the surface of filigree 
work. A plan which is recommended here is somewhat curiously worded : 
u Silver may be cleaned in water in which potatoes have been boiled, and a 
superior polish is thus imparted to them.” Under copper we find some 
interesting particulars regarding the copying of wood engravings in that 
metal. Successful deposits of large wood blocks of the Illustrated London 
Neics have been formed and taken off in eight hours ; and electrotype blocks 
used in printing The Times are stated to have furnished twenty million im- 
pressions before the surface was unfit for further use. As regards the 
deposition of nickel, to which attention has recently been drawn, we learn 
that although the metal is much less expensive than silver, the cost of nickel- 
plating is not proportionately less. In the Special Technical Section of the 
art of electro-metallurgy, the author describes the various forms of batteries 
in use ; figures of the forms devised by Wollaston, Smee, and Daniell are 
provided, the batteries of Bunsen and Grove, however, are only illustrated by 
the coke bar used in the one, and the porous cell employed in the other. 
The use of batteries has in some cases been superseded by the introduction of 
magneto-electric machines and thermo-electric piles. A gramme machine, 
such as is employed by the firm of Chris tophle of Paris, when worked with 
one horse power at a speed of 300 revolutions per minute, will deposit 600 
grammes of silver per hour. Clamond’s pile, of the kind used in Birming- 
ham, London, Sheffield, and other places, when burning 150 litres of gas 
per hour, will deposit one kilogramme of copper. 
FERNS.* 
T HE study and cultivation of those interesting and often exquisitely 
beautiful plants, the Ferns, are now so very general that it need be no 
matter of surprise to find that the literature relating to them is constantly 
on the increase. We have now before us two excellent works on ferns. 
One of them is a new edition of Mr. John Smith’s handbook of ferns, in 
which that gentleman, whose experience in this department of botany, and 
especially in the cultivation of the plants during his long service as Assistant 
Curator of the Botanic Gardens, at Kew, rendered him one of the first 
* “Ferns: British and Foreign. The History, Organography, Classifi- 
cation, and Enumeration of the. Species of Garden Ferns. With a Treatise 
on their Cultivation, &c., &c.” By John Smith, A.L.S. New and Enlarged 
Edition. 8vo. London : Hardwicke & Bogue. 1877. 
“ The Fern World.” By Francis George Heath. 8vo. London : 
Sampson Low & Co. 1877. 
