NA TURE 



91 



THURSDAY, JULY 22, 1909. 



THE DRESSING OF MINERALS. 



The Dressing of Minerals. By Prof. Henry Louis. 

 Pp. x + 544. (London: Edward Arnold, 1909.) 

 Price 30s. net. 



THE author says, in his preface : — 

 " The object of the present work is to give an 

 account of the theory and practice of the dressing- of 

 minerals, which will, I hope, prove useful to the 

 miner or metallurgist who desires to understand the 

 principles upon which this art is based, as alsoto the 

 manufacturer who supplies the necessary appliances, 

 and above all to the student who is preparing for 

 either of the above professions." . . . " I_ have dis- 

 regarded the time-honoured division which would 

 make separate branches of the dressing of ores, and 

 the cleaning of coals." 



The first impression produced on reading this state- 

 ment it that the new departure is warranted ; that 

 there are many points in common in the two branches, 

 and that the comparison of practice under the different 

 conditions would be of an illuminating character. 

 The further perusal of the book, however, seems 

 hardly to "bear out this promise, and the joint treat- 

 ment of the two branches rather tends to confusion, 

 for the cleaning of coal involves the use of so many 

 methods that are inapplicable to ores and vice versa 

 that, if the two branches are to be treated in the same 

 book, they should at least be dealt with under different 

 sections. 



Difficulties, inherent to the method adopted of 

 dealing with the subject, are found throughout the 

 book, and it is practically only in the chapter on 

 general construction of dressing works that any clear 

 differentiation between coal and ore dressing appears. 

 It may be that the manufacturer should be acquainted 

 with the machines used in both classes of work, and 

 even that the student should acquire a knowledge of, 

 and be able to draw comparisons between them, but 

 that coal-miners should be called upon to study the 

 various forms of rock-breakers, stamps, and other 

 crushing mills and fine grinders seems unnecessary. 



The book is well written and interesting, more 

 especially, perhaps, in those parts that deal with 

 theoretical considerations which relate to the con- 

 struction of the machines. The designs of various 

 machines are illustrated by excellent plates, and 

 leading dimensions are often given, as well as the 

 cost of the machines and manufacturers' figures re- 

 garding capacity. The latter are sometimes apt to 

 be high ; for instance, it is stated on p. 140 that a 

 pair of Krom rolls 26 inches diameter by 15 inches face 

 will crush about two tons of average ore per hour to 

 about 30 mesh. 



Relatively little information, however, is given as to 

 setting up machines, their adjustments or running, 

 the general conditions that have to be fulfilled or the 

 general care of a dressing plant. Early forms of 

 machines and historical references have received a 

 good deal of attention, possibly more than they 

 deserve, while in many cases modern forms have been 

 NO. 2073, VOL. 81] 



passed over with brief mention, and a statement that 

 they have not been long enough in use to enable an 

 opinion to be formed regarding their value. 



The treatment of the subject is divided into general 

 considerations; volumetric sizing; sorting and wash- 

 ing; comminution; separation by specific gravity; 

 appliances depending essentially on vertical fall; jigs; 

 horizontal current separators; shaking tables; pneu- 

 matic, magnetic, and electrostatic separation; separa- 

 tion by surface tension; accessory appliances and 

 general construction of dressing works. 



It is, perhaps, in the chapter on volumetric sizing 

 that the treatment of coal and ores together is most 

 objectionable. It is sometimes difficult to gather 

 whether the machine spoken of is used for coal or 

 ores, and although, of course, many of them could be 

 used for both, there is a more or less clear line of 

 distinction between the two. To find a Wilfley impact 

 screen described between the Klein screen and 

 Zimmer conveyor screen seems curious. Trommels 

 are said to be satisfactory to ,V'"ch mesh. ^ In the 

 chapter on comminution such varying machines^ as 

 rock breakers, rolls, Huntingdon mills, ball mills, 

 tube mills, and disintegrators have been dealt with all 

 too shortly. The Griffin mill is passed over in one 

 paragraph, in which it is described as " like the 

 Huntingdon mill with a single large roller which is 

 caused to revolve on its spindle by means of gearing," 

 but the construction, mode of action, and causes of 

 crushing are so different in the two machines that the 

 Griffin certainly merits a fuller description. 



It seems questionable whether vanners should be in- 

 cluded under the title of shaking tables, and no 

 distinction is made between the condition of a pulp 

 adapted for a vanner and that for a shaking table. 

 The number of discussions that have taken place, and 

 tests that have been made to prove whether it is better 

 to classify the pulp or not before treatment on 

 vanners, do not appear to be mentioned, while an 

 authoritative pronouncement on the subject would 

 have been of interest. 



The subject of pneumatic separation has been 

 treated more fully than it appears to deserve, and 

 machines described which have certainly not war- 

 ranted their existence. Magnetic separation has also 

 received a good deal of attention, and many machines 

 are figured which are used both for strongly and 

 feebly magnetic substances. 



In dealing with separation by surface tension, the 

 author says it is impossible to offer correct or saris- 

 factory explanations of the observed phenomena. He, 

 however, presents an historical account of the de- 

 velopment of the processes which depend upon this 

 property, and briefly refers to several of the flotation 

 processes. He has, however, only described the 

 Elmore oil process and the Elmore vacuum process m 

 any detail, from which it would seem that, in his 

 opinion, they only are worthy of consideration.^ The 

 chapter on accessory appliances passes from tipplers 

 to various ore bin gates, then comes back to creepers, 

 and returns to various conveyors of the belt, bucket, 

 scraper, and screw types. Car and bucket elevators 

 and tailings-wheels are dealt with, as well as ore 



