AQUATIC PRODUCTS AS FEKTILIZEKS. 271 



acconliiig- to llio species and the season. Even wlien llie nioisl iiie is 

 largely removed the quantity of fertilizing substances in tlie dried 

 material is small. However, if the quantity of oil in the waste is 

 sufficient to pay the cost of its extraction, it is usually profitable to 

 perform the sliglit additional labor necessary to make the material 

 suitable for fertilizer. The manurial content of fish heads is rela- 

 tively large, and whenever they are accumulated in large quantities 

 their conversion into fertilizer is profitable. 



A convenient process of converting a small quantity of refuse from 

 dressing fish into fertilizer is to store it in a receptacle made in the 

 ground. This should be about 5 or 6 feet deep, with the area depend- 

 ing on the amount of refuse, but usually about G feet square. It 

 should be dry and if the soil is sandy some clay should be spread at 

 the bottom. First is placed a layer of wood ashes a few inches deep 

 and then an equal layer of fish refuse covered by a sprinkling of lime. 

 Then follow another layer of ashes, one of fish refuse sprinkled with 

 lime, and so on until the hole is full. It should be covered with earth 

 or sod and these covered with weighted boards and permitted to so 

 remain for several months. The fish refuse quickly disintegrates 

 and becomes mixed with the ashes, forming an excellent fertilizer. 



Since 1875 the skins and bones resulting from the preparation of 

 boneless codfish have been used for fertilizing purposes. After 

 desalting them and extracting the glue, the remaining material is 

 dried and sold for 115 or $20 per ton. The annual product amounts 

 to about 3,000 tons. Most of this is produced at Gloucester, Mass., 

 with smaller quantities at Boston, Provincetown, Portland, and Vinal 

 Haven. According to analyses, this fertilizer contains about 10 or 

 12 per cent of phosphoric acid, 8 or 9 per cent of nitrogen, and 5 or 

 6 per cent of moisture. 



The refuse in preparing oil from livers of cod, sharks, and related 

 species, from heads of halibut, sturgeon, and sword-fish, and from 

 other materials is also dried and sold for fertilizer. The liver scrap 

 formerly sold at $8 or 110 per ton, but at present its market value is 

 onlj^ about half of that amount. Fertilizer made from fish heads 

 is especially rich in phosphoric acid. A sample of guano made in 

 Boston from fresh cod heads showed 20 per cent of phosphoric acid, 

 6| per cent of nitrogen, and 3| per cent of moisture, and a sample of 

 that made from fresh halibut heads contained 13 per cent of phosphoric 

 acid, 5^ per cent of nitrogen, and 5 j)er cent of moisture. 



An important fish fertilizer in Norway is made from the refuse in 

 dressing cod for drying, consisting principally of heads and back- 

 bones. These are merely dried by spreading them on the rocks and 

 are then broken and ground to the condition of coarse bone-meal. 

 In some localities the refuse is first steamed, to facilitate the drying 

 and grinding. The utilization of these materials for fertilizer was 

 begun about 1855, and the industry is centered at the Lofoden Islands, 

 the location of the principal cod fishery of Europe. The present 



