have been satisfactory, as the number of bricks which have shown. condensation is small.

POROUS HOLLOW-TILE LINING OF 3-INCH BATTERY.

This battery has been lined with book tile, medium light in color, smooth on the exposed face. The tiles were placed next the concrete forms and the concrete rammed in back of them.

The lining has not been very satisfactory for two reasons; first, the tile is too hard and the surface too smooth and impervious. As a lining it is much less efficient than the cheaper red hollow partition brick used in a number of other emplacements.

The shape and dimensions of the tile used and the manner in which it was placed are illustrated in the drawing.

LINING USED IN ALL THE ROOMS OF 12-INCH BATTERY.

The lining is illustrated in the drawing herewith. The walls are lined with 2-inch hollow porous brick. The bricks were placed against the forms and the concrete rammed in back of them. The vertical joints are filled with cement mortar, and the bricks were placed in position just ahead of the concrete gang, so that the mortar of the concrete should join with the mortar in the joint and form a tongue of cement which would hold the bricks firmly in place. No other means of holding them against the concrete wall was used. There has been no report received of any bricks similarly supported being loosened in this or in other batteries by target practice.

As shown, the ceiling is a metal lath supported on the lower flanges of the I beams, with a plastering of very porous mortar. The mortar was made in the porportions of 1 barrel of cement to 2 barrels of slaked lime. The surface of the plastering was left as rough and porous as possible. A smooth finish was carefully avoided.

Both the hollow bricks in the walls and the coarse plastering overhead have so far been entirely effective in preventing condensation. One 12-inch gun emplacement has been similarily lined and has shown no condensation, and a similar lining in one emplacement of a 6-inch battery has been equally satisfactory. Porous hollow tile similar to the above were used both on the walls and ceilings of the rooms in one traverse of one mortar battery, but there has been some condensation at times, though not by any means as much as would have taken place on a less porous surface. Why there should be condensation here and not in other rooms similarly lined is not clear unless the tile used should be too hard burned and not sufficiently porous.

As the age of the battery exercises an influence upon the amount of condensation that may take place, it should be stated that the 12-inch gun emplacements have undergone their second season's test, the 6-inch battery and the mortar battery their third year's test.

COPPER AND WOOD LININGS OF MAGAZINES IN OLD GUN EMPLACEMENTS.

The rooms were habitually wet by leakage. A waterproof lining next the concrete was therefore necessary to collect this leakage. This lining was made of 16-ounce copper, soldered together in the shop into as large sheets as could be conveniently handled, the remain

ing joints being soldered after the sheets had been placed in position against the concrete walls and arched ceilings.

To prevent condensation a lining of magnesia lumber in one room and of wood in the others was used, the inner lining being supported on strips, the latter being secured to the walls by screw bolts. The details of the lining are shown on thedeg. In designing the lining the idea was to take up as little as possible, as the rooms

were already too small to store the desire amount of ammunition. Wherever a bolt passed through the copper lining, a washer of felt saturated in melted vaseline was placed next the copper to prevent leakage.

A hair-felt inner lining shown on one of the sketches has not been tried.

The leakage through the concrete has been effectively excluded, but the wood and magnesia lumber do not prevent condensation. As a precaution against condensation this lining is a failure.

Very respectfully, your obedient servant,

Brig. Gen. G. L. GILLESPIE,

S. W. ROESSLER, Major, Corps of Engineers.

Chief of Engineers, U. S. Army.

B B B 2.

DEFENSES OF PORTSMOUTH, NEW HAMPSHIRE, AND BOSTON, MASSA

During the winter of 1902-3 the magazines in two 8-inch emplacements, thirteen 10-inch emplacements, five 12-inch emplacements, and one mortar battery were lined for the purpose of endeavoring to prevent percolation and condensation. The general method which was followed in this work was to put in a waterproof lining held in place with wood. In the magazines where there was the greatest percolation the waterproof lining was of copper. In others the waterproof lining was of Paroid" roofing paper, and in others a combination of the two was tried, using copper on the ceiling and "Paroid" on the sides.

66

In placing the lining in the magazine the general method where copper was used was to place the planks which were to hold the copper ceiling in place on trestles at a convenient height above the floor of the magazine say, about 4 feet. This formed a platform upon which the copper could be spread and the sheets soldered together, making a perfectly waterproof layer. The copper was also extended down over the sides of the planking about 1 foot. After the soldering was completed the ceiling was jacked up into place by the aid of jacks placed under the wooden planking. It was held in place temporarily by studding, the copper for the sides of the room placed and soldered, the side sheathing planks placed and joists nailed lengthwise of the room to the upper part of the side planking to hold the ceiling in place.

The temporary studding could then be removed, buying the room clear, only about 2 inches from each side of the room being taken p with the waterproofing. Where "Paroid" was wood men wubspot layer the lining was held in place by mwana of bolte at in the walle and ceiling. Hoses were dried in woont 6 inches, bulke sak wod grouted in place. Woot

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ing joints being soldered after the sheets had been placed in position against the concrete walls and arched ceilings.

To prevent condensation a lining of magnesia lumber in one room and of wood in the others was used, the inner lining being supported on strips, the latter being secured to the walls by screw bolts. The details of the lining are shown on theg. In designing the lining the idea was to take up as little as possible, as the rooms were already too small to store the desire amount of ammunition.

Wherever a bolt passed through the copper lining, a washer of felt saturated in melted vaseline was placed next the copper to prevent leakage.

A hair-felt inner lining shown on one of the sketches has not been tried.

The leakage through the concrete has been effectively excluded, but the wood and magnesia lumber do not prevent condensation. As a precaution against condensation this lining is a failure.

Very respectfully, your obedient servant,

Brig. Gen. G. L. GILLESPIE,

S. W. ROESSLER, Major, Corps of Engineers.

Chief of Engineers, U. S. Army.

B B B 2.

DEFENSES OF PORTSMOUTH, NEW HAMPSHIRE, AND BOSTON, MASSA

During the winter of 1902-3 the magazines in two 8-inch emplacements, thirteen 10-inch emplacements, five 12-inch emplacements, and one mortar battery were lined for the purpose of endeavoring to prevent percolation and condensation. The general method which was followed in this work was to put in a waterproof lining held in place with wood. In the magazines where there was the greatest percolation the waterproof lining was of copper. In others the waterproof lining was of "Paroid" roofing paper, and in others a combination of the two was tried, using copper on the ceiling and "Paroid" on the sides.

In placing the lining in the magazine the general method where copper was used was to place the planks which were to hold the copper ceiling in place on trestles at a convenient height above the floor of the magazine-say, about 4 feet. This formed a platform upon which the copper could be spread and the sheets soldered together, making a perfectly waterproof layer. The copper was also extended down over the sides of the planking about 1 foot. After the soldering was completed the ceiling was jacked up into place by the aid of jacks placed under the wooden planking. It It was held in place temporarily by studding, the copper for the sides of the room placed and soldered, the side sheathing planks placed and joists nailed lengthwise of the room to the upper part of the side planking to hold the ceiling in place.