262 CHEMICAL MANURES. 



comes from the vats, is more or less dark, according to the im- 

 purities contained in the raw material. Three classes are dis- 

 tinguished, white tallow, yellow tallow, and green tallow. The 

 paler it is, the more it is valued by candle-makers and soap-makers. 

 It is again boiled so as to skim it, and eliminate the impurities which , 

 accompany it. It is afterwards run into casks ready for delivery. 

 After removing the tallow, what remains in the boiler (disintegrated 

 flesh, bones completely detached, the largest of which are removed) 

 is put into a press which removes 15 per cent of water and dried. 

 The Butchers Union of Paris, in its Aubervilliers factor}^ uses two 

 systems of driers, one naked fire, the other steam. In the steam 

 drier, Donard's system (Fig. 51), drying lasts seven hours at the most. 

 The naked fire drier resembles an enormous coffee roaster, fitted with 

 an agitator ; it is driven by the central shaft ; its furnace is arranged 

 like that of a boiler ; dr^dng lasts at least ten hours ; the amount of 

 coal consumed is enormous. Donard's dryer is much more economi- 

 cal and has the great advantage of yielding an absolutely inodorous 

 powder. The drying operation is complicated by the comparatively 

 large quantity of fat which the meat and bones retain after boiling, 

 and which has not risen to the surface with the tallow. This fat 

 renders the substance to be dried tacky ; it is inflammable, especially 

 when air is blown over it at a high temperature. The products 

 coming from the dryer are brought on to a sorting sieve which 

 throws the bones on one side, and delivers the finely powdered 

 meat on the other side ; the latter is bagged up for delivery. By the 

 use of Donard's dryer all this work can be done in less than twenty- 

 four hours, from the time the meat entered the factory until it is 

 bagged up in the state of powder ; 100 kg. of pressed material yield 

 33 kg. of dried matter ; 100 kg. of pressed material correspond to 

 140 kg. of original material. Meat meal is sold according to its 

 percentage of nitrogen. The following is its average analysis : — 



TABLE LXXIV.— COMPOSITION OF MEAT MEAL. 



Pel' cent. 



Water « 



Tallow • . . . . B 



Nitrogen ......... 4-tt 



Phosphoric acid ........ lo 



The liquors from the boiling are collected into two cisterns, where 

 they are left to deposit for several days. Their muddy deposit, 

 somewhat rich in organic matters, is taken ujd by a montejus and 

 poured over a very vast area with raised edges, to let it drain better, 

 then mixed with meat from the boilers or put directly into Donard's 

 dryer. At the Aubervilliers factory they treat 805 tons of meat, etc., 

 per month, which yield 15'8 per cent of tallow, 150 tons of dried 

 meat, and 50 tons of bones. 



