262 REPORT—1840. 
the Chemical Section of the British Association at Birmingham, 
passes summary judgment upon, by affirming that ‘the con- 
dition, sine gud non, for efficaciously protecting readily oxidable 
metals against the action of free oxygen, being dissolved in fluids, 
is to arrange a closed voltaic circle, made up on one side of the 
metal to be protected, and another metallic body more readily 
oxidable than the former, and on the other side, of an electrolyte 
containing hydrogen—for instance, water.’’ Whatever opinion 
may be formed as to the necessity of a closed circle, it is un- 
doubtedly not proved that the evolution of hydrogen is the con- 
dition of protection, sine qua non; the experiments adduced do 
not show it, while many others might be quoted directly show- 
ing it not to be a necessary condition. This is not, however, the 
place for discussing Professor Schonbein’s views at length, which 
involve the whole guestio vexata of the chemical and contact 
theories of galvanism. 
252. I proceed, therefore, to notice the seventh column of 
this Table, in which is given the loss of weight sustained by the 
alloys of copper and zinc while in presence of cast iron and the 
solvent. On inspecting this column it will be apparent that 
the losses have not taken place in accordance ‘with the law 
of volta-equivalents: there can be little doubt that they are 
strictly in accordance with that law, and that the results are ir- 
resoluble from the involvement of two or more series in column 
seven, arising probably frem some of the alloys being simple 
binary compounds, and others either double binary alloys, or a 
mixture of a binary alloy with one or other of its components in 
excess. 
253. It will be further observed, that whereas zinc alone in 
protecting cast iron suffered a loss of = 2°95 grains, being 
nearly the equivalent, the alloy (23 Zn + 8 Cu), which as fully 
protected the iron from all action or corrosion, sustained a loss 
but of =0°51 grain; in other words, the protecting metal was 
scarcely itself acted on at all. 
This, then, makes a by no means unimportant step towards 
obtaining the much-wished-for electro-chemical protector before 
spoken of; and henceforth the engineer will have it in his 
power, whenever the alloy (23 Zn +8 Cu) can be used or applied 
in contact with cast iron, to protect the latter as fully as by 
zine itself; yet with a protector which shall suffer scarcely 
any loss, and whose protective energy I have reason to suppose 
will be, from this very cause, much more permanent and inva- | 
riable than I have already proved that of pure zinc to be. 
254. With respect to the alloys themselves found in this 
Ninth and following Table, I believe so large and complete a 
