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Infusorial Earth and its Uses . [July, 
times added to the silica to assist in binding the material 
together. Such bricks, we are told, were made in ancient 
times, and were described by Posidonius and Strabo, and 
particularly commended by Vitruvius, Pollio, and Pliny. In 
1791 they were again brought into notice by Giovanni 
Fabroni, in Tuscar.y, who, after many trials, succeeded in 
making bricks which would float upon water. Their strength 
was but little inferior to that of ordinary bricks ; they are 
remarkable not only for extreme lightness, but also for their 
infusibility, and for being very poor conductors of heat ; 
they may be held at one end while the other is red-hot. As 
an experiment, Fabroni constructed the powder-magazine 
of a wooden ship with these bricks ; the vessel being set on 
fire, sank without explosion of the powder. In 1832 Count 
de Nantes, and Fournet, a mining engineer, used them in 
constructing powder-magazines and other parts of ships, 
thus lessening danger from fire. From an earlier source 
(“ Encyclopaedia Americana,” ii., 266) we are informed that 
these floating bricks, made of agaric mineral or fossil farina, 
—infusorial earth, — has been found, on account of its in- 
fusibility at the highest temperatures, to be extremely useful 
in constructing reverberatory furnaces, pyrometers, and 
magazines of combustible materials, while their lightness 
and non-conduCting qualities render them particularly useful 
for the construction of powder-magazines on board of ships. 
In agriculture, the use of the infusorial earth has been 
suggested as a manure for lands poor in silica, which substance 
enters importantly into the constitution of the stalks and 
outer coverings of cereals. Quite an animated controversy, 
indeed, has of late sprung up as to the merits of infusorial 
silica as a component of fertilisers, an idea which forms the 
essential feature of a patent lately issued to Messrs. N. and 
G. Popplein, Jun., of Baltimore. It would be foreign to the 
purpose of this sketch to enter into a discussion of the 
merits of this controversy, involving as it does the introduc- 
tion of certain debatable questions in agricultural chemistry ; 
but the ideas of the Messrs. Popplein have aroused on the 
one hand such warm championship, and on the other such 
opposition, that a concise statement of the points in dispute 
may not be amiss. 
The manufacturers before named, proceeding from the 
well-known faCt that the relative quantity of silica in the ash 
of the cereals is greatly in excess of what is required for the 
normal combination with the bases (potash, soda, &c.) found 
therein, claim that in the ordinary course of things it is 
impossible for Nature to furnish to cultivated lands for 
