These are formed by adding to ordinary fat lime or feebly hydraulic mortars such a proportion of pozzuolana (see p. 196) as will make good their deficiency in clay. This proportion depends upon the composition of the lime in the mortar to be improved.

The success of pozzuolana mortar depends upon the intimate mixture of the ingredients, which should be reduced to a fine powder, and ground in a mill for 20 to 30 minutes.

Good pozzuolana mortar behaves like that made from eminently hydraulic lime.

Alkaline Silicates, produced by boiling flints in an alkali, may be added to mortar in the form of a thin syrup.

They are found to greatly quicken the setting of fat lime mortars, makingthem to resemble hydraulic limes and cements in this respect, according to the quantity used, but they do not materially increase their strength.

Table Showing The Force Necessary To Tear Apart Common Stock Bricks

TABLE showing the Force necessary to tear apart common Stock Bricks, bedded one across the other, with various qualities of Cement and Lime, the Joint in each case having a Sectional Area of about Twenty Square Inches.

Nature of Lime or Cement.

Composition.

Age 14 days.

Age 21 days.

Age 28 days.

Age 35 days.

Lbs per sq. inch in

28 days.

Remarks.

Portland Cement

1 cemt

,6

sand

166

lbs.

206

lbs.

313

lbs.

309 lbs.

151/2

lbs.

Portland with less than four parts of sand would be out of the question in point of price.

,, ,, • •

1 ,,

5

,,

304

,,

336

,,

325

,,

433 „

161/4

,,

,, ,, • •

1 ,,

4

,,

217

,,

367

,,

463

,,

520 „

23

,,

Blue Lias lime .

1 lime

3

sand

63

,,

,,

,,

Blue Lias lime (Selenitic) .

1 ,,

6

,,

172

,,

237

,,

249

,,

286 „

12 1/2

,,

,, ,,

1 ,,

5

,,

161

,,

268

,,

233

,,

267 „

11 3/4

,,

,, ,,

1 ,,

4

,,

144

,,

268

,,

253

,,

283 „

121/2

,,

,, ,, ,,

1 ,,

3

,,

259

,,

235

,,

252

,,

308 „

12 1/2

,,

Barrow Lias lime

1 ,,

4

,,

110

,,

141

,,

137

,,

• • •

6 3/4

,,

,, ,,

1 ,,

3

,,

143

,,

137

,,

183

,,

...

9

,,

Barrow Lias lime (Selenitic)

1 ,,,

6

,,

270

,,

409

,,

399

,,

430 „

20

,,

One of the best English limes.

,, ,,

1 ,,

5

,,

177

,,

572

,,

399

,,

438 „

20

,,

,, ,,

1 ,,

4

,,

233

,,

292

,,

418

,,

539 „

21

,,

,, ,,

1 ,,

3

,,

255

,,

388

,,

541

,,

435 „

27

,,

White chalk lime

1 ,,

3

,,

66

,,

97

,,

93

,,

..

4 3/4

,,

White chalk lime (Selenitic)

1 ,,,

6

,,

207

,,

221

,

218

,,

..

10 3/4

,,

,, ,,,

1 ,,

5

,,

215

,,

243

,,

243

,,

...

12 1/4

,,

,, ,,

1 ,,

4

,,

179

,,

197

,,

197

,,

..

9 3/4

,,

,, ,,

1 "

3

,,

160

,,

199

,,

209

,,

..

10 1/2

,,

Burham lime (Selenitic)

1 ,,

6

,,

203

,,

343

,,

408

,,

556 „

20 1/2

,,,,

,, ,,

1 ,,

5

,,

291

,,

424

,,

368

,

490 „

181/2

,,

A first-class, clayey Medway lime, selected for Selenitic mortar, and now supplied by Messrs. Lee for the purpose.

,, ,,

1,,

4

,,

336

,,

385

,,

454

,,

430 „

22 3/4

,,

,, ,,

1 ,,

3

,,

325

,,

454

,,

484

,,

424 „

24 1/4

,,