14 Chemical Composition and Commercial Value of 



50 per cent, of their weight of sea-salt, and to expose this mix- 

 ture to a current of steam placed in a furnace or cylinder at a 

 temperature a little below red heat. 



If, as is sometimes the case, the nodules do not contain a 

 sufficiency of silica, the deficiency must be made up previous to 

 the operation. 



M. Roblique remarks : " The reaction of silica on chloride 

 of sodium (salt) in contact with the vapour of water is well 

 known, resulting in the formation of silicate of soda and hydro- 

 chloric acid. In this special case the latter acts on the phosphate 

 of lime, from which it takes two equivalents of lime, and gives 

 rise to chloride of calcium and biphosphate of lime. All the 

 phosphoric acid does not, however, combine with the lime; it 

 sometimes forms a considerable quantity of phosphate of soda. 

 The same process thus furnishes in the dry state, without excess 

 of acid, both silicates and phosphates, which readily yield to 

 plants not only silica and phosphoric acid, but also a considerable 

 quantity of alkali." 



I have not been able to learn if this plan has been tried on a 

 large scale and been found practicable. If, by any cheap 

 method not necessitating the use of sulphuric acid, coprolites 

 could be brought into a state in which the phosphates they con- 

 tain can be readily taken up by plants, a great saving would be 

 effected. I question, however, very much whether this new plan 

 can be successfully carried out on a large scale, but think it well 

 worth a trial. 



5. MARACAIBO OR MONK'S ISLAND GUANO (AMERICAN 

 PHOSPHATE). 



This singular phosphatic mineral was originally introduced 

 into commerce under the name of Maracaibo Guano. It is also 

 known as Columbian Guano, also as Monk's Island Guano, and 

 is sometimes simply described as American Phosphate. 



It occurs in large lumps, in which are frequently pieces of quartz- 

 rock imbedded. These lumps are hard, and have a compact 

 interior of a chocolate-brown colour, and a grayish-white mam- 

 millated exterior, resembling an enamel. Between this enamel- 

 looking portion and the compact interior is a lighter brown 

 porous structure. 



It is reduced under a millstone with some difficulty into a 

 brownish-gray powder. Burned in an open platinum capsule, it 

 turns beautifully white, showing that it contains organic matter, 

 which imparts a chocolate-brown colour to the lumps in their 

 natural state. 



A fair average sample, prepared by reducing to powder por- 



