653719-1891-Report-Whitish-Appearance-Taitam---Pokfulam-Waters — Page 3

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THE HONGKONG GOVERNMENT GAZETTE, 26TH SEPTEMBER, 1891. $837

solution, but in the decomposition of the Silicates. The porosity of rocks which such a penetration presupposes is of a very general character, even as regards the most compact rocks. Calcium Silicate is readily decomposed by a solution of Carbonic Acid, Alkaline Carbonates, but Magnesium Silicate is unaffected by either. Of the substances present in spring water, some such as the Earthy Carbonates are no doubt derived from direct solution of the rocks, but there are others such as the Alkaline Car- bonates which do not exist in any rocks. Such substances can only be supposed to originate from the decomposition of the minerals contained within the rocks. It is such a decomposition of minerals contained in rocks that in my opinion causes the whitish appearance of the Taitam and Pokfulam waters. This is not peculiar to Hongkong, but is known in a few other localities, one of which is Worcester, England. The action may be shortly described as consisting in the abstraction of the whole of the Alkali, two thirds of the Silica, and the assumption of water as shewn in the following simple chemical equation :-

Soda felspar.

Nag Al Ole Sis

Water.

Carbon dioxide.

+

H2O

4 Si O,

Silica.

+

8

H, Al, Os Sig

Kaolin. ***

Co Na Co2 ----—

Sodium Carbonate.

An ultimate product being a hydrated silicate of aluminium, existing as a soft white unctuous powder known as Kaolin. This on account of its low specific gravity and extremely fine state of division remains suspended in the water for an indefinite period, and practically defies simple filtration, even in small quantities except through its own sediment.

13. The following is an extract from a report on the Worcester Water Supply, by the Citys Analyst, Mr. H. SWETE:—

"The water is taken from the Severn one mile above the city, passed through filter beds of sand and gravel, (which are cleansed weekly) then pumped up to a reservoir on a hill, "and supplied by gravitation to dwelling houses; 1,600,000 gallons are pumped daily. The "water contains peat and kaolin (white-water) from the decomposition of the Felspathic "rocks in Montgomeryshire......White-water cannot be clarified by filtration.”

Below are the results of an analysis of the Worcester Water, and for the sake of comparison I attach a copy of a recent analysis of the supplies here. I refrain from making any further comment beyond pointing out that if the Carbonate of Lime in the Worcester Water Supply was removed, the figures for practical purposes would be identical. The amount of Carbonate of Lime in the Worcester Water is indicated by the degree of hardness :---

Results expressed in grains per imperial gallon.

Appearance in a 2 feet tube, .......

Worcester.

..brown and opaque.

Taitam.

Pokfulam.

slightly opalescent. clear and colourless."

Smell when heated to 100° F. Total solid matter dried at 212° F..

slight

none

none

15.54

2.57

...

4.4

Chlorine,

1.83

.63

.84

Hardness,

10.4

.1.20

1.2

Ammonia,

none

none

none

Albumenoid Ammonia, .......................

.0084

none

trace

Phosphoric Acid,..

trace

none

none

Nitrogen in Nitrates,

.029

trace

trace

Oxygen absorbed at 80° F. in 4 hours,...

.1680

.002.

.0025

14. ANALYSIS OF THE MINERAL CONSTITUENTS:-So far as I am aware a complete mineral analysis of the Hongkong water supply has never been published. This being the case, and feeling that an exact knowledge of the mineral constituents of the water would be of value, I have made a careful analysis of the Pokfulam filtered water, and state the results below in grains per gallon.

Actual total solids.....

5.01.

Loss on heating,.

Sodium Oxide,

Potassium

"

Alumina, Ferric Oxide,

Silica,

Calcium Oxide,

.300

.659

.132

.224

.917

.721

Magnesium

Carbon Dioxide,

Chlorine,

.035

.932

.800

Sulphuric Anhydride,

.224

Nitric,

trace

Phosphoric

none

27

Total solids by determination,

..4.944