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POPULAR SCIENCE REVIEW. 
phenomena ; also absorption certainly increases with conductivity. Hence, 
although, if a method of experimenting were employed in which a water- 
condenser of great internal resistance were discharged through wires of less 
resistance for shorter and shorter periods of time, the measured specific 
inductive capacity might get less and less, and gradually approach a value 
equal to the square of the index of refraction of water for infinitely long 
laminous waves (the index of refraction for air being called unity) ; still, 
practically, the measured specific inductive capacity can never be even 
approximately equal to the refractive index of water, since the absorbed 
charge is immeasurably greater than the surface-charge.” We therefore 
need not expect to find the specific inductive capacity of water in its varia- 
tions with temperature consistent with Dr. Gladstone’s results for index of 
refraction. 
Neio Form of Battery. — M. P. Jablockkoff describes to the Academie des 
Sciences a pile in which the attackable electrode is of coke. This substance 
not being attacked by any liquid at ordinary temperatures, heat was needed, 
and a substance which would only become liquid at a sufficiently elevated 
temperature, and be converted into vapour only at a still higher. 
He fused nitrate of potass or of soda, and immersed in it as the attack- 
able electrode ordinary coke, with platinum as the unattackable. For the 
latter, however, iron answers equally well. The electromotive force of this 
battery varies between two and three units. It is, therefore, superior to that 
of Bunsen or Grenet, the former of which gives 1*8 unit, the latter 2*0, or 
at best 2T units. 
Previous fusion of the nitrate is not necessary. It is sufficient to ignite a 
piece of coke, and place it in contact with the powdered salt. The heat 
produced fuses the salt, and action begins. The action is not at all rapid. 
Much carbonic acid and other gas is liberated, and is stored up to act as a 
motive power. 
Inc?'U8tation in Boilers . — The value of zinc in this capacity is now fairly 
•established ; and is probably due to galvanic action. Facts have been col- 
lected by M. Brossard de Oorbigny; and M. Lesueur has stated the 
case of a steamer repaired in 1861 at Havre. It had three boilers, one of 
which, fed direct from the sea, was almost wholly oxidized and useless, 
while the others, which were fed with water from the condenser, were in 
perfect preservation. The condenser showed that the brass partitions were 
reduced to a comparatively pure spongy copper, the zinc having disappeared 
entirely. It was concluded that zinc could be made to act as a scale-pre- 
venter. In 1876 M. de Oorbigny was requested to examine closely all 
the evidence, and to report to the Ministry of Public Works. The applica- 
tion of the zinc was generally in the simplest form, it being placed in a part 
of the boiler removed from the furnace. It was found that, with fair water, 
containing but little calcareous matter, the deposits, instead of forming 
adherent scale, were in the state of fluid mud, and easily removed by wash- 
ing. If, however, the feed-water was strongly calcareous, the deposits were 
coherent and strong, but did not adhere to the iron, being easily removed by 
the hand, assisted by a scraper. The zinc was in time found to be reduced 
to a white earthy-looking oxide, consisting of 87*30 per cent, of this sub- 
stance, with 3*80 of oxide of iron and aluminium, and 6*20 of lime carbonate. 
