ORGANIC NITROGEN FERTILIZERS in 



generally only obtained in small quantities, and is for the most 

 part converted into poultry food ; the herring refuse and 

 the special products obtained from livers are retained for 

 fertilizing material. Under modern conditions of work, the 

 materials are generally first cooked in jacketed vessels, with 

 stirrers resembling paddles. At the same time, a strong 

 draught of air is carried through these cookers by means of a 

 fan. Thus, not merely is the odour, which is extremely 

 objectionable, carried away, but the steam is carried away 

 at the same time, consequently the fish refuse becomes dry. 

 Winter whitefish needs practically no other process than 

 cooking, and 30 cwts. of whitefish produce 6-7 cwts. of 

 poultry food, but with other materials more elaborate 

 systems of manufacture are carried out. When livers are 

 available, these are boiled with steam and water, and the 

 oil skimmed off the surface as far as possible ; the remainder 

 is then half-cooked, or partly dried by the steam paddle 

 described above. 



The semi-dried fish is then sent to an extracting plant, 

 which most conveniently consists of a horizontal boiler 

 enclosed and fitted with stirrers, so as to maintain the 

 contents of the boiler in constant agitation ; the boiler 

 is " lagged " with the usual heat-preserving materials. A 

 second plant preserves a partial vacuum, so that the tempera- 

 ture at which water is given off is lowered ; at this stage 

 of the process a further drying may take place if considered 

 advisable. One of the great objects in heating at the early 

 stages of the process is to coagulate the albuminoids, other- 

 wise the material would be in such a colloidal condition that 

 it would be difficult to obtain any separation between solid 

 and solvent. Benzine, or crude petroleum naphtha, or the 

 lighter fractions from the shale oil industry, are added at 

 the rate of about 600 gallons to a 5-ton lot of dried fish 

 refuse. The materials are slowly and steadily mixed up by 

 the internal revolving paddle, and, should it be necessary 

 that the contents be dried before proceeding any further, 

 the space around the apparatus is heated with steam, and 

 the vacuum somewhat increased, so that the benzine vapour 



