﻿26 BULLETIN 2, U. S. DEPARTMENT OF AGRICULTURE. 



facilitate the discharge of this cake; the curb being larger at the 

 bottom than at the top, the cake falls out readily. At this stage, the 

 scrap contains about 50 per cent water, by weight, and about 6 or 

 9 per cent of oil. In its warm and moist condition it makes an ideal 

 breeding place for various flies and for the growth of decay-produc- 

 ing bacteria. Unless it is to be immediately dried, it is treated with 

 crude sulphuric acid (" about a dipper full (3 quarts) to a cart- 

 load ") in small but sufficient amount to discourage the development 

 of insect and other life therein. The acid, besides acting as a pre- 

 servative, brings about a disintegration of the flesh and bones of 

 the scrap. It is claimed to " dissolve " the bone and to " fix the 

 ammonia." It does render a larger proportion of the phosphoric acid 

 of the bones " available " and may possibly convert some of the 

 nitrogen of the complex organic bodies in the flesh into ammonia, 

 to form ammonium sulphate. What is meant by this fixation prob- 

 ably is that the decay of the fish, leading to the loss of nitrogen or 

 possibly to the actual liberation of ammonia, is prevented. This 

 so-called " acidulated " or crude scrap may be sold as such, or, as 

 opportunity presents, finally may be dried. 



DRYING (OLD METHOD). 



The old platform dryer has been supplanted in almost every 

 factory on the Atlantic coast by the modern and more rapid hot-air 

 dryer. As must be inferred from the name, the platform method 

 consists merely in spreading the scrap on a platform, where it is ex- 

 posed to the air and sun. The platform in some cases is built of 

 boards raised a few inches from the ground and in some cases is 

 made of concrete. The scrap is frequently stirred either by hand 

 rakes or hoes or by scrapers drawn by horses. At night, or when 

 rain is threatened, the scrap is raked into heaps and covered with 

 canvas. Under favorable conditions, three days drying is required. 

 The product obtained by this method of treatment is a much lighter 

 brown in color than that dried by hot air. Its odor is also less 

 marked. It is said that considerable ammonia is lost by thus expos- 

 ing the scrap so thoroughly and for such a long time to the air. 

 Whether fish scrap loses nitrogen on exposure to air when in a 

 nearly dry condition and when no recognizable decay is taking place 

 is a mooted question. Experiments bearing on this point are under 

 contemplation in this laboratory. 



COOKING (NEW METHOD). 



The new method of cooking fish has largely supplemented the old 

 because of its speed and efficiency and the saving in labor which it 

 effects. The apparatus employed is essentially a long, narrow, iron 

 cylinder (PL III), of varying length, but frequently about 40 feet, 



