For the diameter of the feed-pump ram, the square of the diameter of the cylinder in inches x 011 the diameter in inches.

For the cubical content of the steam-room, the square of the diameter of the cylinder in inches × 9÷40=content in cubic feet.

For the cubical content of inside fire-box above fire-bars, the square of the diameter of the cylinder in inches÷4=content in cubic feet. For the inside diameter of the steam-pipe, the square of the diameter of the cylinder in inches x 03 the diameter in inches. For the diameter of the branch steam-pipe, the square of the diameter of the cylinder in inches × 021 the diameter in inches. For the diameter of the top of the blast-pipe, the square of the diameter of the cylinder in inches × 017 the diameter in inches.

For the diameter of the feed-pipes, the diameter of the cylinder in inches x 141 = the diameter in inches.

For the diameter of the piston-rod, the diameter of the cylinder in inches 7 the diameter in inches.

For the thickness of the piston, the diameter of the cylinder in inches x 2÷7 the thickness in inches.

For the diameter of the connecting-rod at the middle, the diameter of the cylinder in inches x 21 = the diameter in inches.

For the diameter of the plain part and inside bearing of the crankaxle, the cube root of the square of the diameter of the cylinder in inches x 96 = the diameter in inches.

For the diameter of the outside bearings of the crank for axle, the cube root of the product of the square of the diameter of the cylinders in inches x 396 the diameter in inches.

For the diameter of the crank-bearing, the diameter of the cylinder in inches x 404 the diameter in inches.

For the length of the crank-bearing, the diameter of the cylinder in inches × 233 = the length in inches.

Remarks on Steam-Engine Boilers and their Proportions.

For engines designed to give a gross indicator horse power of at least twice the nominal horse power, the grate surface should be 66 or 69 square feet per nominal horse power, but may be increased to 75 square feet, and should never be diminished to less than 60 square feet as a minimum.

The area of opening over the bridges or through the tubes, should be 125 square feet, or 18 square inches per horse power, and inay be increased to 143 square feet, or 20 square inches with advantage, particularly in tubular boilers, and should never be diminished to less than 15 square inches, or 109 square feet per horse power.

The area of chimney should be 076 square feet, or 11 square inches, but may be increased to 13 square inches, and should never be diminished to less than 10 square inches per horse power.

The heating surface in fire-places and flues should be 14 square feet per horse power, exclusive of all bottom surface, but may be increased to 15 square feet, and should never be diminished to less than 12 square feet per horse power.

In calculating tubular boilers the whole surface of the tubes should be taken, and there should be a total of 17 square feet per horse power in the fire-places and tubes.

In engines designed to work to a gross power in the cylinder by the indicator greater than twice the nominal horse power, these proportions must be increased; or, if the reverse be intended, they may be diminished in proportion.

Of the Pressure of Steam, in Inches of Mercury, at Different

Temperatures.

Of the Temperature of Steam at different Pressures in Atmospheres.

To PREVENT SPONTANEOUS COMBUSTION.-It is a fact better ascertained than accounted for, that fixed oils, when mixed with any light kind of charcoal, or substances containing carbon, such as cotton, flax, or even wool, which is not of itself inflammable, heat by the process of decomposition, and after remaining in contact some time, at length burst into flame. This spontaneous combustion takes place in waste cotton which has been employed to wipe. machines, and then thrown away and allowed to accumulate into a heap. We have known an instance of the kind in a manufactory for spinning worsteds, where the waste wool, or "slubbings," as it is termed in Yorkshire, was thrown into a corner and neglected. It then heated, and was on the point of bursting into flame, when the attention of the workmen was directed to the heap by the smoke and smell. In cotton mills the danger exists in a still greater degree, and it is believed that the destruction of many cotton factories has been occasioned by this means. The cause of this peculiar property of fixed oils deserves more attention than has hitherto been paid to it.

TABLE.

Of the Elastic Force of Steam, and Corresponding Temperature of the Water with which it is in Contact.

Of the Force and Temperature of Steam in Atmospheres.

TO WRITE ON SILVER WITH A BLACK WHICH WILL never go off.— Take burnt lead and pulverize it. Incorporate it next with sulphur and vinegar, to the consistency of a painting color, and write with it on any silver plate. Let it dry, then present it to the fire. so as to heat the work a little, and it is finished.

of Water.