AQUATIC PRODUCTS AS FERTILIZERS. 267 



the cylinder is filled with steam, which heats the scrap, thereby 

 evai^orating most of the moisture. 



Labor-saving devices make tlie handling of the scrai) almost auto- 

 matic. From the presses it is transferred to the drier by means of 

 screw conveyors and bucket elevators, and is fed intermittently^ in 

 quantities of 200 pounds at intervals of 45 to GO seconds. The capac- 

 ity of a drier is 2^ to 3 tons i^er hour, and the largest factories usually 

 have 2 drying machines. From these the scrap is conveyed to the 

 storage room. 



Although the term "dried" is popularly applied to all scraj) from 

 which a large iDortion of the moisture has been removed by evaporation, 

 its use in a technical sense refers to scrap containing not to exceed 

 12 per cent of moisture. In modern factories, green scrap fresh from 

 the presses contains from 45 to 50 per cent of water. When desic- 

 cated so that only 10 per cent of its weight is water, each ton of chum 

 or green scrap yields about 1,156 pounds of " dried scrap." It is not 

 always that so large a quantity of water is eliminated, and sometimes 

 the finished scrap contains 25 and even 35 per cent of moisture. 

 Owing to its tendency to lose nitrogen in the form of ammonia and 

 its unsuitability for storage or transportation, the scrap containing a 

 high percentage of moisture is for use principally in the vicinity of 

 the factories. 



Not all the scrap, however, is dried, a large percentage being treated 

 with sulphuric acid for the purpose of "fixing" the ammonia, pre- 

 venting fermentation, and dissolving the bones. To every ton of 

 scrap, from 80 to 200 pounds of sulphuric acid of about 50° strength 

 is added and thoroughly commingled, the quantit}^ of acid used deftend- 

 ing to some extent on the state of the weather and the extent of 

 decomposition of the fish. This is conveniently done by depositing 

 the green scrap in handcarts of 1,000 pounds capacity, wheeling 

 these to an elevated i3latform and dumping the contents beneath, 

 when the heap is immediately sprinkled with about 60 pounds of sul- 

 phuric acid contained in a leaden pot. After a short while the bones 

 dissolve and the mass becomes homogeneous and of a rich brown color, 

 instead of the former grayish color. The ammonia is fixed by the 

 acid and the tendency to decomposition overcome. The scrap is then 

 conveyed to the storage room and shipped in bulk as required. 



Instead of sulphuric acid, the solid granular sodium sulphate has 

 been used to mix with the scrap, about 90 pounds being thoroughly 

 combined with each ton. While this method is somewhat cheaper 

 than applying sulphuric acid, it is not so satisfactory-, and sodium sul- 

 phate is now little used for this purpose. 



Owing to the difficulty in drying the scrap, most of that prepared 

 at the Northern factories is acidulated, while the bulk of the South- 

 ern product is dried. In the last year for which data are available, 

 the product of the entire coast was 48,853 tons acidulated and 36,077 



