108 CHEMICAL MANURES. 



done that perfect solution is realized, and that a superphosphate 

 that will behave well on subsequent manipulations is obtained. Of 

 recent years attempts have been made to use hot sulphuric acid and 

 inject hot air into the chamber, so as to render the phosphate 

 perfectly soluble and to start the drying of the superphosphate, so 

 as to simplify the final operations. But the results obtained were 

 not satisfactory. The opinion of certain specialists may be endorsed. 

 Such experiments will never be successful, because it is irrational to 

 •exceed a temperature of 100° C. (212° F.) in the "den " except in 

 the case of phosphates of very good quality of which there is no need 

 to fear retrogradation. It is better to leave the substance to itself dur- 

 ing its chemical transformation and let it be settled by insensible 

 gradations. Experience shows, moreover, that the injection of hot 

 air into the mass gives it the consistency of mastic, and that the 

 manure manufacturer always tries to avoid, knowing full well that 

 the porosity of the superphosphate is the best condition to realize for 

 subsequent operations. The construction of the decomposition house 

 or "den " is not very complicated. The Vv^alls are two-brick thick ; 

 they are covered inside with a coating which resists acid. To con- 

 solidate them and prevent them yielding under the pressure of the 

 mixing, they are fortified by iron T pieces, fixed to the base by 

 masonry, and joined to the roof by cramping irons. The roof 

 consists of iron T pieces, three feet apart, laid on the vralls and con- 

 nected together by iron rods or arches of masonry, the whole being 

 covered by a coat of cement. All the ironwork is covered by paint 

 to resist acid fumes. The house is fitted with a solid oak or pitch 

 pine door consolidated inside by planks placed crosswise in the 

 gutters. The chinks of the planks and the door are luted with a 

 paste of clay so as to prevent air penetrating.^ 



In the early days of manure manufacture only one " house " 

 was used, and the mixer was installed in the centre of the ceiling of 

 the house ; then two houses were installed with the mixer stride-legs 

 hetween them ; finally, later on, four houses have been built and 

 the mixer placed at the crossing of the party walls. This plan gives 

 excellent results. The mixer in that case is fitted with 1 discharge 



1 The great difficulty with the doors is that the acid eats away the bolts of 

 any opening handle ; the men must then perforce lever it open by the pick. The 

 result is that where the pick is applied a chink is formed which gradually 

 enlarges. But it is not a case of &>\x penetrating into the Jionse, but of fumes from 

 the mixer or house esccvping into the air through chinks. Both the district 

 authority and the Local Government Board in Great Britain would at once 

 proceed against any manufacturer letting the fumes escape into the air. If 

 means be taken to prevent the escape of fumes, then it follows, ^9^7- contra, that 

 no air can gain access, because the pressure from within outwards is far gi'eater 

 than from without inwards. The air cannot penetrate until the gaseous fumes 

 have condensed, and th'^n the quality of the manure from that batch is fixed and 

 determined. It is not advisable, however, to open the door too soon, unless in the 

 ■case of hurried mixing specially. The doors are best of pitch pine.— Tr. 



