40 The N.Z. Journal of Science and Technology. [Jan. 
Both the Potter and, Delprat processes depend upon the generation of C0 2 , 
generated through the action of acid on certain constituents of the ore. 
Potter used acid, agitation, and heat; and Delprat a hot solution of salt 
cake. In 1902 Froment came along with his process, in which he used 
oil to attract the bubbles of C0 2 generated by the action of acid on calcite, 
adding the latter if suitable carbonates were not present. He recommended 
a much less quantity of oil than was formerly used. In 1902 Cattermole 
patented a process wherein oil selection is made to sink the mineral 
particles. To an acidified pulp he added from 10 lb. to 15 lb. of oil per ton 
in the presence of an emulsifying agent, such as soap. This mixture was 
first agitated violently, then stirred slowly in order to coagulate the metallic 
particles into masses, which sank while the gangue was floated in an upward 
current of water. In 1904 De Bavay patented a process which contains 
no new features, but rather mechanical alterations. His process can only 
work on sand free from slime. In 1905 the Sulman-Picard patents were 
taken out. The chief point of interest in their patents is that air takes 
the place of chemically generated gas. These patents, as well as those of 
Froment and Cattermole, were secured by the Minerals Separation Company, 
and form the basic principles of their patents. 
Norris, in 1907, was the first to use air without the addition of acid or 
oil as the chief flotation agent. He uses air in solution in water to bring 
about flotation. 
In 1886 Bradford invented a machine in which flotation depended upon 
surface tension. The dry ore is made to meet the surface of a still body 
of water, so that the metallic particles are not wetted, and float, while the 
gangue-particles are wetted and sink. This was the first attempt at flota¬ 
tion without oil. 
In 1904 Macquisten invented a tube machine in which surface tension 
plays the most important part. At a later date acid was added, which 
generated C0 2 from lime in the ore. Still later coal-tar was used in 
conjunction with acid. 
In 1912 Wood patented a surface-tension process. In his process the 
crushed ore (dry) is fed from a vibrating diskin a fine stream into a current 
of water. By retarding the current the gangue is made to sink, while the 
sulphides float on the surface. Surface-tension processes as well as bulk- 
oil processes have now been entirely discarded in favour of flotation by oil 
and gas. 
Description of Main Types of Processes. 
According to the various flotation patents, flotation can be divided 
into •— (a) Froth flotation, Minerals Separation (Callow) ; ( b ) acid flota¬ 
tion (Potter, Delprat) ; (c) surface-tension flotation (Bradford, Macquisten, 
Wood). 
Acid flotation is at present in use at Broken Hill, where the ores 
contain a high percentage of carbonates. These in the presence of acid 
generate C0 2 , which serves as the main flotation agent. An acid process, 
more especially where hot solutions are used, is not a very pleasant one to 
work, for not only have special precautions to be taken to protect all parts 
of appliances used from the corrosive action of the acid, but there is also 
a grave danger in handling acid in bulk. In using the acid process at 
Broken Hill advantage is taken of making use of a by-product in the ore 
to generate C0 2 and so bring about flotation—a result that could only 
otherwise be obtained by installing expensive agitation machinery. 
In froth flotation it is necessary that there should be a selective action 
between the froth-bubbles and the minerals to be floated, and also that 
