IX.--NITRATE OF SODA.

Amount of exports 332
Date of discovery of nitrate deposits 333
The origin of nitrate deposits 334
Forbes and Darwin on the theory of their origin 335
Source of nitric acid in nitrate of soda 337
Guano theory of origin of nitrate of soda 337
Nitric acid in nitrate of soda probably derived from sea-weed 339
Appearance of nitrate-fields 340
The method of mining the nitrate of soda 341
Composition of _caliche_ 342
Extent of the nitrate deposits 342
Composition and properties of nitrate of soda 343
Nitrate applied as a top-dressing 344
Nitrate of soda encourages deep roots 344
Is nitrate of soda an exhausting manure? 345
Crops for which nitrate of soda is suited 346
Method of application of nitrate of soda 347
Importance of having a sufficiency of other fertilising
constituents 348
Conclusions drawn 349

APPENDIX TO CHAPTER IX.

Total shipments from South America, 1830-1893 351
Total imports into Europe and United Kingdom, 1873-1892 351

CHAPTER X.--SULPHATE OF AMMONIA.

Value of ammonia as a manure 352
Sources of sulphate of ammonia 353
Ammonia from gas-works 353
Other sources 354
Composition, &c., of sulphate of ammonia 355
Application of sulphate of ammonia 356

APPENDIX TO CHAPTER X.

Production of sulphate of ammonia in United Kingdom, 1870-1892 358

CHAPTER XI.--BONES.

Early use of bones 359
Different forms