the cylindrical furnace in a condition resembling in appearance coarse gunpowder, with occasional agglutinations of small friable particles readily reduced to fine powder in an ordinary mill, requiring but small power to work, and producing but little wear and tear upon the millstones.  The operation is continuous.  The revolver or furnace, once started, works on night and day, receiving the adjusted quantity of powdered material at the upper or feed end, and delivering its equivalent in properly burnt cement at the opposite end, thus effecting a great saving of time, and preventing the enormous waste of heat and serious injury to the brickwork, etc., incidental to the cooling down, withdrawing the charge, and reloading the ordinary kiln.

Cement, when taken from the furnace, weighed 110 lb. per bushel.  Cement, when ground, leaving 10 percent. on sieve with 2,500 holes to the inch, weighed 121 lb. per bushel, and when cold 118 lb. per bushel.  When made into briquettes, the tensile breaking strain upon the square inch: 

At  4 days was       410 lb. per square inch. 
At  6 days  "        610  "   "     "     "
At 14 days  "        810  "   "     "     "
At 49 days  "        900  "   "     "     "
At 76 days  "      1,040  "   "     "     "

A cylindrical furnace, such as the author has described, is capable of turning out at least 20 tons of good cement per day of twenty-four hours, with a consumption of about 3 tons of slack coal.  It will be readily understood that these furnaces can be worked more economically in pairs than singly, as they can be so arranged that one producer may furnish a sufficient quantity of gas for the supply of two cylinders, and the same labor will suffice; but in order to provide for possible contingencies the author advises that a spare gas producer and an extra furnace should be in readiness, so that by a simple arrangement of valves, etc., two cylinders may always be in operation, while from any cause one may be undergoing temporary repairs, and by this means any diminution in the output may be avoided.

The author considers it unnecessary here to discuss either the advantages or the economy of fuel effected by the employment of gas producers for such a purpose.  These have been abundantly proved in steel and glass making industries, where a saving of from 50 to 70 per cent. of the fuel formerly employed has been made.  Their cost is small, they occupy little room, they can be placed at any reasonable distance from the place where the gas is to be burnt; any laborer can shovel the slack into them, and they do not require constant skilled supervision.  It is claimed by the author of this paper that the following are among the many advantages derivable from the adoption of this method of manufacturing Portland cement, as compared with the old system: 

(1) Economy of space—­the furnaces, with their appurtenances, requiring only about one-fourth the space of what would be occupied by the ordinary kilns for producing the same quantity of finished cement.

    (2) Continuous working, and consequent economy of fuel lost by
    cooling and subsequent reheating of the kiln walls.