Proceedings of the British Association. 67 



before formed a powerful fire, was found to be completely extin- 

 guished. This experiment 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 eX])osed. 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 instrument makers, were placed in a 

 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 zinc, oil of tar, and turpentine ; and 

 others again were set in zinc pillars having small zinc 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 ruM, 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 



