1882.] • COMMERCIAL FERTILIZERS. 79 



trogen but extremly poisonous to plants. Certainly no one should 

 risk an application of such low grade stuff without submitting it 

 first to chemical examination at the experiment station. 



Our other nitrogenous manures are chiefly of animal origin, and 

 have been made available by the progress of our manufactures. 

 One of the most important is fish-scrap, the refuse left after ex- 

 tracting the oil as far as practicable from porgies or menhaden. 

 This industry is not more than thirty years old. Previous to that 

 time the fresh fish had been used on land in considerable quantity, 

 but it is said that the oil of this fish damaged the land and made 

 it unfit for cultivation. The first succcessful attempt to make a 

 profitable manure out of fish is credited to a Mr. Lewis of New 

 Haven, who operated in 1849. His work was suspended after a 

 while, but others no doubt independently soon prepared fish in the 

 same way. The fish were steamed or boiled until disintegrated, 

 then pressed to remove oil, and the cake v/as dried and ground. 

 This is essentially the process employed at present by most manu- 

 facturers. 



The fish are thrown into large vats partly filled, with water and 

 boiled by steam. In from fifteen minutes to an hour the steam is 

 shut off, the oil and water drawn off into settling tanks, and the 

 remaining scrap is put into hydraulic presses and submitted to pow- 

 erful pressure. Considerable gelatine is lost in the soup and con- 

 siderable oil remains in the scrap, together with from 40 to 50 per 

 cent, of water in spite of the pressing. This is removed by solar 

 or steam heat, so that " dry fish-scrap " as we buy it averages about 

 Y^ to 8 per cent, of nitrogen, 6 to 8 per cent, of phosphoric acid, 6 

 to 11 per cent of oil, with from 12 to 20 or more per cent, of 

 water. 



The oil left in the scrap is a loss to the manufacturer and also a 

 damage to the goods, for it hinders decay and makes the scrap less 

 prompt in its action. Two patent processes are or have been in 

 use to obviate this difficulty. Goodale's patent consists in washing 

 the fresh scrap with a sufficient quantity of hot water, which re- 

 moves the gelatine and so releases the oil, for it is claimed that it 

 is this gelatine which retains the oil, and with it and water gives 

 the scrap its slimy consistence and makes the drying such a tedi- 

 ous process. It can then be re-pressed and dried much more easily, 

 and the percentage of oil in the fresh scrap is reduced from say 15 

 to 2 per cent. 



Another process, Adamson's, consists in extracting the oil with 



