Finally, the manure is weighed into gunny bags, holding 2 cwt. each ; the mouths of these are sewn up with coarse twine ; and, in this condition, the manure is conveyed to the land where it is to be used. The bags are seldom fit for re-use, and are more commonly charged for in the price of the manure, remaining the farmer's property. The destruction of the bags by the action of the free sulphuric acid in the manure, and the consequent occasional waste of their con tents, may be much reduced by passing the bags through a mixture composed of 15 per cent. chloride of barium, 10 per cent. chalk, 5 per cent. glue, 5 per cent. glycerine, and 65 per ceut. water, squeezing them between wooden rollers, and drying them. For transport abroad, manures are generally packed in barrels.
Paudrette.—The French word " poudrette " is applied to a preparation of sewage, or rather night soil, with sulphuric acid. The acid is generally added to the excrement in the pails used to trans port it to the works, and the whole is then tipped into a Milhurn'e desiccator, from which, when it has suffered sufficient evaporation, it is removed to a drying-floor heated by flues beneath. It is subsequently passed through a disintegrator, preparatory to being packed for sale. Sometimes a much more complicated system is pursued. The pails are first emptied upon a strainer, constructed to allow all liquid and fine suspended matter to flow through, while retaining the solid faeces, &c. The filtrate is pumped into an elevated tank, for the supply of a boiler capable of dealing with 550 gal. of liquid matter at a charge, and provided with a stirrer, to prevent incrustation. The boiler being charged, 80 lb. of dolomite (magnesian limestone) is added, and the whole is distilled by a Sre below. The ammonia distilled off is conducted into an ordinary saturator, such as is used in making sulphate of ammonia (see Alkalies—Ammonia), containing brown sulphuric acid. The foetid vapours evolved in the saturator are carried through a worm-pipe in the supply tank, partly for condensation, and partly to warm the contents of the tank before running them into the boiler. The condensed vapour is run off into the drains. The sulphate of ammonia thus made is evaporated in a shallow, open, leaden vessel, on the top of the saturator, and as it crystallizes, is drawn out and set to drain. Only I of the ammonia is boiled off. The residue in the boiler, when this proportion has been collected, is run off by a valve at the bottom, and is stirred up with superphosphate in large wooden vats. The product is then dried, either by ordinary means or by pressure. The solid
matters originally separated by the straining are mixed in a mortar-mill with the superphosphate and soot or waste charcoal.
To prevent nuisance arising from this manufacture, the whole process must be conducted within a olosed building. The interior of the desiccator should communicate with a blower, creating an in-draught, sufficient to prevent the escape of effluvia through the crevices of the cover, or while charging the machine. Flues must be provided, so that the blower shall drive the vapours through the fires used for heating the drying-floor, before they escape into the chimney of the works.
Prevention of Nuisance.—In the process of manufacturing artificial manures, such as super phosphate, nitrophosphate, bone-manure, Sre., very offensive and injurious vapours are abundantly evolved ; consequently, a knowledge of how to prevent these vapours from becoming a nuisance to the neighbourhood is of vital importance to those engaged in the industry, particularly iu a densely populated country like England. Only a few of the largest firms have hitherto given much attention to the subject ; but future legislation on the noxious vapours question will probably enforce upon all the precautions willingly adopted by a few.
The objectionable odours are generated chiefly in the kpartments where the manure is mixed, and where it is received after mixing to set and eool—in other words, in the " mixer " and the "den." It is therefore essential that these should be made practically airtight, so that the gases may be kept under control. The first point is to prevent the vapours generated within the mixer from escaping through the hopper by which the solid materials are fed into the mixer. This is most efficiently accomplished by substituting the arrangement shown in Fig. 951 for the ordinary feed-hopper. It consists of a horizontal wooden box, kept completely and constantly full of materials, which are carried into the mixer by means of the archimedean screw working within the box. It car.
only be used when the mixing is continuous.
The manure, on flowing from the mixer, falls into the den, which is a close chamber, constructed of brickwork walls (best lined with cement plaster), and with a paved floor. In the walls of the den, are suitable wide openings for removing the manure when set ; these are firmly closed by stout wooden doors during the mixing. The den is also securely roofed over, either permanently or temporarily, in such e way as to include the outlet from the mixer.