ON MANGANESE BRONZE. 383 
brings up the total cost of the steel blades, on an average, to two or three 
times that of the manganese bronze. 
That the manganese bronze propellers are incorrodible, and in every 
other respect efficient, has now been proved by experience, as some have 
been at work approaching three years, and are as perfect in every respect 
as when first applied. Some time after the introduction of the No. 3 
quality for propellers, the No. 2 was employed for some propeller blades, 
as fears were entertained as to the No. 3 setting up galvanic action and 
corroding the stern frames. Most of these propellers stood well, but 
some of the blades failed, and it was found on examination that the 
castings were unsound, owing to the metal having become deteriorated 
by melting in a reverberatory furnace. In consequence, it has now been 
determined to adhere solely to the No. 3, as this quality has always 
given the greatest satisfaction, both as to its facility in casting and 
efficiency under trial; and further experience proves the supposed 
galvanic action to be only a myth, or if there should be a tendency to it, 
it is effectually prevented by lining the inside of the stern frame with 
zine strips. 
A proof of the soundness and tenacity of the manganese bronze was 
shown in an accident, which occurred to one of the blades of the ‘ Garth 
Castle,’ at its launch from the yard of Messrs. John Elder & Co., in 1880, 
when one of the blades came in contact with the jetty, and was bent 
round, without even a crack, to nearly a right-angle, and was afterwards 
hammered back cold to its original form without detriment. The photo- 
graph exhibited shows the blade from two points of view bent, and the 
other view as hammered back; another photograph shows one of the 
blades of the North German Lloyd’s steamship ‘ Mosel’ (kindly lent by 
Messrs. John Elder & Co.), recovered from the ship after she was 
wrecked, in which the metal was subjected to a still more severe punish- 
ment without breaking than even in the case of the ‘ Garth Castle.’ 
The other qualities, Nos. 4 and 5 of the manganese bronze, have no 
particular claims to strength, but are most effective for the purpose of 
bearings, slide valves, slide blocks, piston rings, &c., and in all situations 
where friction occurs, and are much more durable than ordinary gun-metal. 
Before concluding I may add a few words on the art of brassfounding 
generally, and I cannot help saying that, as at present practised, it 
appears to me to be very far behind what might be expected in these 
days of progress. 
In the manufacture of iron and steel an amount of scientific know- 
ledge has been brought to bear which elevates these industries into 
scientific processes, but I can discover nothing of the kind in bronze and 
brassfounding as ordinarily practised; everything is done by the rule of 
thumb, and that in a most clumsy manner. The idea of combining the 
various metals to form the alloys required in atomic proportions does 
not seem to have been ever entertained, and even the books written for 
the practical guidance of brassfounders, ignore this important principle 
altogether. 
I must not be understood as applying this remark to Dr. Percy and 
Mr. Mallet, and other scientific metallurgists who have drawn attention 
to the subject, and made valuable suggestions respecting it in their well- 
known works ; but I allude to that class of books generally termed hand- 
books, and the like, which contain instructions of the most clumsy and 
unscientific character for making different alloys. Thus for gun-metal, 
