263 CHEMICAL MANUEES. 



value ; they contain 7 to 11 per cent of nitrogen, deducting moisture. 

 Chemical manure manufacturers often treat them in the same way 

 as horn, roasting or steaming in a closed vessel, and grinding. 

 The roasting of tanned leather renders it friable without perceptibly 

 modifying its chemical properties. Steaming under pressure 

 dissolves it to a great extent. The leather liquor is sometimes so 

 concentrated that it takes the form of gelatine, and the amount of 

 ground leather finally obtained scarcely renders the half of that 

 fed into the digester. This method, therefore, is not economical. 

 Moreover, steamed leather has onlv a low value as a manure, for 

 the tannin in the tanned leather prevents the decomposition of 

 the animal matter in the soil, and is only partially destroyed by the 

 heat. The powder obtained from roasted leather is even vrorse. It 

 is true that the manufacturer again finds in it the greater part of 

 the nitrogsn contained in the raw material, and which varies from 

 5 to 9 per cent. There has already been described, in discussing 

 the preparation of bone dust, a process of preparing leather which 

 is more advantageous both for the manufacturer and the farmer. 

 Another method of treating woollen rags, leather waste, etc., was 

 the subject of British patent No. 26,780 of 22 December, 1905. 

 Kaw materials, such as woollen rags, leather waste, previously 

 moistened, if need be, are fed into a horizontal cvlindrical receiver 

 and treated by sulphuric acid which falls on them drop by drop, 

 by means of a pipe running the length of the cylinder. At the 

 same time a rotary motion is imparted to the cylinder whilst inject- 

 ing hot gases from a furnace, then the materials are drenched with 

 salt water, well mixing the whole, and continuing the heat. If 

 leather waste be principally used, it is well to add finely ground 

 phosphate of lime to the acid w^ater. The vapours disengaged by 

 the material are propelled by a pump into a condensation tower 

 lined with bricks, washed by a jet of finely divided water. The 

 non-condensed gases are directed into a filter bed of moss litter, 

 and from there it escapes into the atmosphere ; the final product is- 

 discharged into a pit and reduced to a fine powder.^ 



Comparative Value ofDijferent Nitrogenous Manures. — Peruvian 

 guano is the most active of nitrogenized organic manures. Popp 

 has examined the action, of the nitrogen of organic manures com- 

 pared with that of nitric nitrogen. In his experiments he used all 

 sorts of organic manures, dried blood, horn dust, castor meal, ground 

 raw bones, fish guano, meal, meat meal, Bremen poudrette, wool 

 dust. According to the agricultural experiments which he exe- 

 cuted, he indicates the ratio which exists between the action of the 

 different manures. Under the cover of this remark, the following are 



1 But usin» 120' T\v. acid heated to 140° F., 4 cwt. of raw leather or 2 

 cwt. leather and 2 cwt. shoddy can be got into each ton of compound manure 

 and so well dissolved as not to be seen when the den is opened. So why all this- 

 unnecessary labour and expense ': — Tr. 



