164 Ransome’s Patent Concrete Stone. [ April, 
Works have now been erected at East Greenwich, having a 
frontage on the river, and although not yet to the extent con- 
templated, they even now cover a large area, and will repay a 
journey from town in order to inspect them. The process of the 
manufacture of this artificial stone is exceedingly simple; the sand, 
chalk, or other mineral substance, is mixed with its proper pro- 
portion of a solution of silicate of soda in an ordinary pug-mill, 
and the mixture, which very much resembles in substance fresh 
putty rolled in sand, and is of a very plastic consistence, is either 
pressed into blocks or moulds, or can be rolled into slabs or forms 
as may be desired, and is afterwards either saturated with, or im- 
mersed in, a solution of chloride of calcium, when a double decom- 
position of the two solutions employed immediately takes place. 
The silica combines with the calcium, and at once forms an in- 
soluble silicate of lime, firmly binding together all the particles of 
which the stone is composed, whilst at the same time the chlorine 
combines with the soda and forms chloride of sodium, or common 
salt, which is easily removed, as has been already explained. The 
materials used by the Patent Concrete Stone Company at their 
works at Hast Greenwich are principally sand, gravel, flints, chalk, 
limestone, caustic soda, chloride of calcium, and water. Any quantity 
of the finest sand is obtainable from the neighbourhood of Maid- 
stone ; gravel is to be had at a nominal price from the bed of the 
Thames; chalk and flints are abundant in the numerous pits near 
by; the chemicals are brought by water carriage from the North 
of England, and a plentiful supply of water is furnished by a large 
well which has been sunk in the yard, this supply being supple- 
mented, as required, by the North Kent Water Company. 
The digesters, in which the silicate of soda is produced, are 
suppled with steam from a high-pressure boiler. In the lower 
part of each digester is a coil of steam-pipe, and above this is an 
iron grating upon which the flints are placed. The digester is 
then nearly filled with a solution of caustic soda, of a specific gravity 
of about 1°120, and the steam is admitted into the coil pipe raising 
the liquid to boiling pomt. When this operation has been con- 
tinued long enough the liquid solution is sent into a reservoir, 
whence it is drawn off, from time to time, into pans, in which it is 
evaporated down to a specific gravity of about 1°700; this gives the 
necessary degree of viscidity for the use to which it is to be applied. 
The best stones are made from finely sifted dry sand. A small 
quantity of pulverized stone, or carbonate of lime, is added to the 
sand to give the silicate of lime, produced in the manufacture, the 
necessary closeness of surface for its cementing action. To each 
bushel of this mixture, one gallon of the silicate of soda, prepared in 
the manner stated above, is added; they are then thoroughly in- 
corporated together in a mill, which operation takes only about 
