EEVIEW OF SUPEEPHOSPHATE MANUFACTURE. 69 



This machine did not at first alwa^^s and everywhere give the 

 result expected ; the superphosphates unless suitably dissolved were 

 converted into paste. Such was the state of affairs about 1880. 

 But to follow^ up the treatment of the phosphates : At the outset 

 of the manufacture of superphosphate, the manufacturer was him- 

 self his own chemist ; he submitted his raw phosphates to a series 

 of dissolving experiments, varying the quantity of acid each time. 

 He then sent samples to an analyst of the superphosphates which 

 appeared to have succeeded best, then he applied to the stock of 

 phosphates the treatment established by groping in the dark. 

 Each new raw material required fresh experiments. It is hardly 

 necessary to remark that such a method of working was fertile in 

 disagreeable surprises for the manufacturer. ^ 



1880 to 1894. — In spite of the good quality of the raw phos- 

 phates, and their low percentage of oxide of iron and alumina, 

 hitches in manufacture were frequent, and gradually the need was 

 felt for a permanent control. Thus since 1880, factories of any 

 importance have each a chemist whose duty it is to follow the 

 material throughout all the phases of its treatment.'-^ This control 

 became more urgent when it was observed in certain mixed 

 manures, that a certain amount of the phosphoric acid had retro- 

 graded, that is to say, it had returned to the condition insoluble 

 in water. At the same time the use of Canadian and Norwegian 

 apatite, and Florida and other mineral phosphates, gave off chlorine 

 and fluorine compounds highly injurious to the health of the work- 

 men, and annoying to the neighbourhood. The machine for mixing 

 the acid with the phosphate was then substituted for the treatment 

 in the open den. The first machine of this nature was an inclined 

 cylinder, in which a shaft fitted with blades arranged in a helicoid 

 manner revolved ; it was charged w4th acid and phosphate at the 

 top end, and the mixture w^as run out at the low^er end. Afterw^ards 

 this apparatus w^as replaced by a flat mixer of cast-iron, likewise 

 furnished wdth an agitator, and in which the acid and phosphate 

 were agitated two to three minutes, then run out into a truck under- 

 neath, whilst the gas given off by the phosphate was led out on to 

 the roof through a wooden chimney. These machines answered 

 all requirements so long as only guano or other phosphates rapidly 

 attacked by sulphuric acid were being treated ; however, the pro- 

 ducts were generally awanting in porosity because the greater part 



1 It would be possible to'name several British manure manufactories the work 

 of which was controlled by chemists 15 to 20 years prior to 1871, and flat stone 

 mills were also in use prior thereto. The writer has handled works, laboratory 

 journals of the early fifties, which show the manufacture was even then under 

 strict chemical control by qualified men on the spot. British manure patent 

 literature of the earlier days speaks for itself. — Tr. 



'" See above note. 



