154 The N.Z. Journal of Science and Technology. [May 
rock-particles appeared to be free from mercury sulphide, but loose cinnabar 
was noticeable in some quantity. A further quantity of solution (4T2-per¬ 
cent. Na 2 S) was added, bringing the proportion up to 1 of ore to 4-5 of 
solution. Agitation was continued at intervals for two hours, and the 
charge left standing overnight. Next morning all the cinnabar was dis¬ 
solved, and the solution was filtered. The charge was given a water wash 
with 1 gallon of water, which analysed 0-3 per cent. Na 2 S. The precipita¬ 
tion was performed in two stages—the first to recover the metallic mercury, 
the second the slime precipitate. The amount of aluminium used was 2 oz. 
for 1 lb. of mercury. In the first stage metallic mercury was recovered 
representing 37-5 per cent, extraction, and the slimes retorted with manganese 
dioxide and lime to take care of the volatile hydrocarbon. The result of 
the retorting was equal to 47 per cent, extraction. The total amount of 
-mercury recovered was equivalent to 84-5 per cent, extraction. The slimes 
contained an unknown but appreciable amount of metallic mercury in very 
minute globules which would not coalesce, due no doubt to the presence 
of the greasy hydrocarbon. With a “ clean ” ore the whole of the mercury 
would fall in the metallic state. The regenerated solution analysed 2-97 
per cent. Na 2 S. The aluminium shavings were made by turning up a bar 
in a lathe ; they were made 1 in. wide, and were thin enough to see day¬ 
light through pin-holes. Precipitation was carried out in an extractor-box 
built after the plan of zinc extractors in cyanide plants. The determination 
of the Na 2 S solutions was made by titrating with a standard alkaline zinc 
solution, using a freshly prepared sodium nitro-prusside solution as an 
indicator. 
The result of this series of tests enabled a satisfactory conclusion to be 
arrived at in regard to the successful treatment of Puhipuhi ore, and 
suggests that the ore should be crushed in solution first by stamps to about 
16-mesh, then through a tube mill reducing the whole to a slime, from which 
the solution could be separated by means of a filter-press or a vacuum- 
filter. 
SURFACE FRICTION OF FLUIDS. 
By E. Parry, B.Sc., Public Works Department, N.Z. 
Of all the branches of engineering, that concerned with the flow of water 
through pipes and channels is the one which suffers most from ambiguity 
and uncertainty. A large number of conflicting formulae are in existence, 
all empirical and evidently based on a very narrow range of experience. 
This state of affairs is due to the lack of a theory which would enable the 
apparently conflicting results to be harmonized, and the position may be 
likened to a hypothetical state of affairs which would exist in the practice 
of designing columns in the absence of Euler’s theory. The latter provides 
a sort of physical parameter—viz., l/nk —in terms of which the limiting stress 
on any column may be expressed, where l is the length of the column, n a 
number, and k the least radius of gyration of the section. Strange to say, 
