HYDRAULIC LIMESTONE. 
75 
It should be observed that a great improvement has been introduced into the process of 
burning lime, which consists in the use of refuse screenings or dust of anthracite for fuel, 
instead of wood, and the employment of the perpetual kiln. The coal dust is said to have 
cost $1.75 per ton in the city of.New-York, while from fifty to seventy-five cents per ton 
were paid for its transportation to Thomason. 
Here, then, we have the singular fact that fuel is transported from the city of New-York 
to Thomason, and the lime procured by its agency again brought to New-York. Now the 
lime thus obtained must be greatly superior to that which is produced from our limestones, 
or else our citizens have been strangely neglectful of their interests in this respect. I have 
reason to believe that the counties of Westchester, Putnam, Orange and Dutchess, contain 
limestones which would yield lime equal to any elsewhere manufactured. And with the im¬ 
provements already introduced into our lime-kilns, as well as into those of Maine, one would 
suppose that our lime could be afforded at a much cheaper rate in the city of New-York, than 
that which is transported from a distant part of the United States. This subject commends 
itself to the enterprize of our fellow citizens.* 
HYDRAULIC OR WATER LIMESTONE. 
It is well known that the lime obtained by the calcination or burning of the different kinds 
of limestone differs greatly in its properties. When the limestone is pure, the resulting lime 
is also of uniform purity. Upon the addition of water to such lime, a high degree of heat is 
produced, its bulk is greatly increased, and it at length falls to powder. This powder, when 
mixed with water and a due proportion of sand, and afterwards exposed to the air, gradually 
acquires a stony hardness; but this result is not produced when the mixture is submitted to 
the action of water. Now these are designated by the name of air limes; and their relative 
value depends in some measure upon the kind of limestone, and the particular mode of cal¬ 
cination. 
But certain impure limestones, when subjected to calcination, afford limes which, while 
they do not undergo much change by simple exposure to the air, do not slake when moistened 
with water, but when reduced to powder, absorb this liquid without producing much increase 
in volume, and without the evolution of much heat; and they moreover form with it a paste 
possessing little tenacity, and which, when placed under water, hardens after the lapse of a 
few days. These are now known by the name of Hydraulic or Water Limes. They differ 
much in the rapidity with which they harden under water, and in the degree of solidity which 
they ultimately attain. 
There are still other limestones, which afford limes possessing the remarkable and very 
useful property of becoming hard almost instantly, like plaster of Paris, whether exposed to 
the air or in contact with water. These are sometimes called Roman cements. It should be 
* According to the last census returns, the value of bricks and lime manufactured in the State was $1,213,326. 
