702 Proceedings of the Royal Society 
because in certain circumstances, which led them to anticipate 
no action, they nevertheless found lead in water, but only in 
extremely minute and unimportant proportion. The test for lead, 
the hydrosulphuric acid, when employed in the way now usually 
practised, is so delicate as to detect that metal dissolved in ten 
million parts of water, and even more. But facts warrant the con¬ 
clusion that the impregnation must amount to at least ten times 
as much before water can act injuriously on man, however long 
it may be used. 
2. On the Preservation of Iron Ships. By 
James Young, Esq., of Kellie. 
My attention was called in January last year to the rusting of 
iron vessels by observing that the bilge water of my yacht (the 
“Myanza,” 214 tons) was much discoloured by red oxide. Knowing 
that bilge water is apt to become acid, and thus to attack iron, the 
result was easily accounted for. Even when the water does not 
become acid, we may expect some action on the iron to take place 
when sulphuretted hydrogen exists, as it frequently does there, in 
which case, first a sulphide, then an oxide, and some sulphate, are 
formed. The remedy seemed to be easy, because the acid can be 
neutralised by lime. This earth would also prevent the formation 
of sulphuretted hydrogen. 
I put this immediately into practice, adding lime until the bilge 
water was alkaline; and samples were taken every fourteen days, 
which showed the amount of rust to be rapidly diminishing. After 
six months the liquid became perfectly clear, so that the cure is 
complete. The yacht is a composite one, and the action is there¬ 
fore greater than in iron vessels generally, because of the copper 
or cupreous bolts which are used. These bolts cause galvanic 
currents with the iron, and greatly assist in its oxidation and 
solution. 
As a very little lime will last a long period, the plan causes 
neither trouble nor expense. Seeing in the newspapers that the 
destruction of the “ Maegara ” was attributed to the action of bilge 
water, I thought that my experience might be of some value. 
