r,
and washed with distilled water; 1 ounce of calcined borax is now
added to every 12 ounces of the mixture, the whole rubbed together in
a porcelain mortar, melted in a clean crucible, and poured out into
pure cold water. This melting and pouring into water must be done
three times, using a clean, new crucible each time. The third frit is
pulverized, five drachms of niter added, and then melted for the last
time, when a clean, beautiful white crystal mass results.

C. M. S., of Wis.--There are no precise proportions observed in
making the coal-tar and gravel walks of which you speak. The aim is to
saturate the gravel with the hot tar without surplus. The interstices
of the gravel are simply to be filled, and the amount required to
do this depends wholly upon the coarseness or fineness of the gravel
employed.

W. P. T., of Ohio.--Two teams of horses, of equal strength, pulling
against each other, by means of a rope, would create the same tension
in the rope, as one of the teams drawing against an immovable object.

W. H. B., of Va.--Ice can be made by compressing air, and, after it
has radiated its heat, allowing it to extract the heat of water with
which it is brought into contact. The temperature of air at 59 deg. Fah.,
would be raised, by compressing the air to one fourth its original
volume, to 317 deg. Fah; and the air would radiate and absorb again, in
expanding, about 190 units of heat.

E. T. H., of Ga.--The friable sandstone, a specimen of which you send
us, may, we think, be rendered firmer by soaking it in a solution of
silicate of soda, and allowing it to stand till dry.

J. A. V., of Ohio.--The use of steam expansively, by means of cut-off
appliances, enables the expansive force of the steam to be utilized,
which cannot be done when the pressure is maintained at one standard,
and steam admitted through the fall stroke. It takes no more power
to do a given amount of work in one case than in the other, but more
boiler capacity, and more fuel, as the working power of the steam is
more economically applied when the cut-off is used.

Geo. F. R., of Ohio.--Type metal is composed of 3 parts lead and 1
part antimony for smallest, hardest, and most brittle types; 4 of
lead and 1 of antimony for next grade; 5 of lead and 1 of antimony for
medium sizes; 6 of lead and 1 of antimony for larger types; and 7 of
lead and 1 of antimony for the largest.

E. J. M., of Texas.--The term "power of a boiler