and Water used for General Purjposcs. 
137 
tanks and its conveyance through iron pipes are frequently 
attended with inconvenience, lor the hydrated oxide of iron, pro- 
<luced by the action of the water upon iron, gives a reddish-brown 
colour to the water, and renders it muddy to an extent which 
entirelv prevents its use for household purposes. With a view- 
to preventing the corrosive action of soft water upon iron, it has 
been recommended to substitute galvanized iron for plain cast- 
or sheet-iron. I find, however, that galvanized iron is not an 
efficient protection against the corrosive action of water ; and 
instances have been brought under my notice in which tanks 
made of galvanized iron were attacked more rapidly than plain 
cast-iron tanks. In galvanizing iron it is difficult, if not prac- 
ticably impossible, to cover the surface of the iron with metallic 
zinc so completely as not to leave here and there small particles 
of iron of a rough surface unprotected by zinc ; and it appears 
to me that a true galvanic action is set up by the water in contact 
with the tw'o metals — iron and zinc forming a galvanic pair — in 
virtue of which action the iron is more rapidly corroded than in 
the case of ungalvanized-iron tanks. 
As an example of the inconvenience of the storage of soft 
water in galvanized-iron tanks, and its distribution through iron 
pipes, I may mention a case which has lately been submitted to 
me. A gentleman residing in the country wrote to me : — 
" I am in a great difficulty as regards the worlcing of a boiler at the back 
of my kitchen grate. This boiler is connected with a cistern in the upper 
part of the house, and this cistern is supplied with our lake water by means of 
A ball-cock. 
The boiler and hot-water cistern are connected together by two 2-inch 
iron pipes, the whole was mounted by one of the first makers in London. 
The cistern supplies hot water to two baths and to some housemaids' closets. 
After being at work some eighteen months a very slow delivery of hot water 
was gi-adually observed, and finally, on examination, one of the pijies at least 
(»he downward floor) was found to be nearly choked with the material, a 
sample of which I hand you for examination. This material seems to line 
the whole of the pipe, even that part which is placed vertically. I should 
observe that the lower end of the supply-pipe dipping 15 inches into the 
boiler appears to be corroded and the zinc eaten away from the iron. 
" You analysed the water some two or three years ago and pronounced it 
to be very good. In fact, filtered, we 'use it now as drinking-water. Nearly 
the whole of it is drainage water. Will you kindly examine the substance 
and give me your opinion as to its origin." 
On examining the dark-brown material which nearly choked 
up the supply-pipe, I found the bulk to consist mainly of 
hydrated oxide of iron, with small quantities of carbonate of 
lime, silica, and magnesia, some carbonic acid, and traces of 
sulphuric acid, manganese, and zinc. 
The following is its composition, when dried at 212° Fahr. : — 
