EEVIEW OF SUPEEPHOSPHATE MANUFACTURE. 71 



\eyoYS (with a useful effect of 85 per cent) inaugurated a new era 

 in the manufacture of superphosphates. It is closely connected 

 with electricity, the ingenious applications of which allow the use 

 of mechanicar equipment in all parts of the factory where it would 

 be impossible to erect shafting. Electricity and aerial conveyors 

 form a sort of connecting link between the different appliances in 

 the factory, and contribute greatly to their increased output. 

 Electric light spreads cheerfulness in all directions; the electric 

 motors driven from a central station work silently in the most 

 distant parts of the factory, the different organs of which thus work 

 in perfect harmony. A "vexed question is that of knowing the 

 treatment to which' superphosphates should be subjected from the 

 moment it is shifted from the den, so as to obtain in the most 

 simple and the most rapid manner a good product which will 

 keep well. To solve it, numerous processes have been elaborated, 

 all converging to the same end, which is to secure a dry pulverulent 

 phosphate easily distributed by the drill sowing machine. The 

 point of departure of these researches was Florida phosphate, which 

 from 1880 [? 1890] was and still is one of the most important raw 

 materials of superphosphate factories, afterwards the phosphates of 

 Tennessee, Algeria, and Tunis. Superphosphates made from Florida 

 phosphate are distinguished by a high percentage of free phos- 

 phoric acid which gives them a damp feeling when touched. The 

 rhost simple means of remedying this inconvenience consists m 

 drving them, and thus quite a series of driers have been constructed 

 for the purpose. At the present time all superphosphates, and 

 especially those intended for export, are dried. But it was soon 

 observed that if drying diminished the percentage of moisture m 

 the superphosphate, it increased their percentage of free phosphoric 

 acid, and of hvdrofiuosilicic acid, and in such conditions, whilst 

 appearing dry, they possessed the property of attracting moisture 

 and attacking the canvas of the bags.^ In 1896, it was found that 

 degelatinized bones, and more recently Gafsa phosphate, afforded 

 simple means of drying superphosphates and rendering them pulveru- 

 lent without exposing them to retrogradation. This point will be 

 reverted to in the sequel. At the same time several specialists m 

 this kind of work, independently of each other, have tried to find 

 methods of obtaining good superphosphates whilst imparting great 

 rapidity to the working process. In this way the grating machine 

 was invented (Heymann and Nitsch's process). But experience 

 proved that perfect"^ results could only be obtained by finely dividing 

 the superphosphates from the mixing den and by diminishing then- 

 free acidity. This result has been fully obtained. Owing to im- 

 proved equipment, means are available of producing from all raw 



1 Steeping in gum kino extract is found in Australia to render manure bags 

 rot proof. — Tc. 



