P38) 
V. 
THE KIESELGUHR OF COUNTY ANTRIM. By JAMES 
HOLMS POLLOK, B. Sc. 
[Read, January 18; Received for Publication, January 21 : 
Published, Marcu 13, 1899.] 
Some considerable time ago I received from Mrs. Hartley a sample 
of Kieselguhr from county Antrim to exhibit at the Conversazione 
of the Royal Dublin Society. Afterwards I noticed, in Pliny’s 
“Natural History,” the remarkable statement that the Romans 
were acquainted with a brick that floated. The passage says :— 
“‘ At Pitane, in Asia, and in the cities of Maxilua and Calentum, 
in Farther Spain, there are bricks made which float in water when 
dry, the material being a sort of pumice earth, extremely good for 
the purpose when it can be made to unite”; and in the Bohn 
edition there is a footnote saying these bricks have been imitated 
by Fabrioni with a light argillaceous earth found in the territory of 
Sienna. 
It occurred to me that the floating bricks of ancient Rome 
could probably be reproduced from the county Antrim Kieseleuhr, 
and on trial it made a brick that floated exceedingly well when 
first placed in the water, but soon absorbed water and sank, exactly 
in accordance with Pliny’s statement. By coating the bricks over 
with a thin skin of paraffin wax to prevent absorption of water 
they are rendered permanently buoyant. 
An analysis was then made of the specimen I had received, 
and its composition found to be:— 
Per cent. 
Silica, . ‘ ‘ ; Hey) 
Alumina, é : 3 9°8 
Ferric Oxide, : ; 5:4 
inte sae : e ; 1:5 
Magnesia, . : 0-1 
Water and Organic Matter, 12-0 
Sr 
SCIEN. PROC. R.D.S., VOL. IX., PART I D 
