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Proceedings of the British Association. 67 
before formed a powerful fire, was found to be completely extin- 
guished. 'Thisexperiment was twice repeated, with equal success. 
- On the application of Native Alloy for Compass pivots, by 
Capt. E. J. Johnson, R. N. 
Among those portions of a ship’s compass which most affect 
its working, are the pivots and caps on which the needle and card 
traverse, and which like the balance of a chronometer (but of far 
more importance to the practical navigator) should not only be 
fitted with the most scrupulous attention to accuracy, but be 
made of materials capable of maintaining a given form under the 
trials to which such instruments are necessarily exposed. Hav- 
ing examined a great variety of compasses which had been used 
at sea, wherein Capt. J. noticed that the pivots were generally 
injured, and often by rust, he searched numerous records of ex- 
periments for its prevention, and for improving the quality of steel 
in other respects, by means of alloys of platinum, palladium, sil- 
ver, &c., (alluding particularly to the experiments of Dr. Fara- 
day and Mr. Stoddart,) and Mr. Pepys having obligingly sup- 
plied Capt. J. with specimens of similar kinds of steel to those 
used by them, these examples, together with pivots made of the 
ordinary kind of steel, and hardened and tempered in the manner 
recommended by eminent instrament makers, were placed ina 
frame for experiment; and to these again Capt J. added certain 
contrivances of his own, such as rubbing a steel pivot with sal- 
ammoniac, then dipping it into zinc in a state of fusion, and af- 
terwards changing the extreme point. Some specimens he coated 
with a mixture of powdered zine, oil of tar, and turpentine; and 
others again were set in zinc pillars having small zine caps, through 
which the extreme point of the pivot protruded, after the man- 
ner of black lead through pencil tubes. ‘The whole of the spe- 
cimens were then placed in a cellar, occasionally exposed to the 
open air, examined from time to time during more than half a 
year, and their several states, as respected oxidation, duly regis- 
tered. The general result was, that not any of the kinds of steel 
pivots used in this trial, except such as were coated with zinc, re- 
mained free from rust, while the pivot made of the native alloy 
which is found with platinum, completely retained its brilliancy. 
Capt. J. then applied to this singular substance a more severe test, 
first by placing sulphuric acid, and then nitro-muriatic acid upon 
it; but even under this trial he could not observe that any change 
had been effected, although the blade of a penknife subjected to 
a 
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