174 Mr. Nixon on the Curvature of Spirit'Levels. 



i. Some small drops of fused ore, which very much resem- 

 bled the imperfectly reduced ore of a in the first experiment, 

 occupied the bottom of the tube immediately at the end of the 

 lime ; but there was not a particle of pure lead formed in any 

 part of the tube. 



k. Four hundred grains of the gray-coloured lumps de- 

 scribed in paragraph J] were assayed with borax and tartar ; 

 and a button of lead weighing 138 grains was obtained. From 

 this lead a small globule of silver weighing j§5_Jth grains 

 was extracted by cupellation, which is after the rate of 13 oz. 

 3 dwts. 10 grs. per 21 cwt. avoidupois of lead, and is not 

 more than might be expected from the sample of galena sub- 

 mitted to experiment. 



From these experiments it appears, 1st, that the vapour 

 of water is decomposed by transmission over heated galena, its 

 hydrogen uniting with a portion of the sulphur to form sul- 

 phuretted hydrogen gas, and its oxygen combining with the 

 equivalent quantity of galena to foi'm sulphate of lead, to which 

 the milkiness of the water in the two experiments is to be at- 

 tributed. The galena, which gives up a portion of its sulphur 

 to form sulphuretted hydrogen gas, is probably reduced to the 

 state of sub-sulphuret of lead. 2ndly, Quick-lime is used in the 

 large way to reduce the slags or scoriae from lead ore into a pasty 

 state, so that they can be more easily removed from the hearth 

 or furnace ; but it appears to have a very inconsiderable ef- 

 fect in promoting the reduction of galena ; and hence the quan- 

 tity used should be no more than may be sufficient to effect the 

 purpose for which it is applied. 3rdly, The deposition of galena 

 from its vapour in contact with steam in a highly crystalline 

 form is an interesting circumstance. The crystals exactly 

 resembled in appearance many specimens from the numerous 

 lead-ore veins traversing the mountain limestone of this di- 

 strict, and might warrant at least the conjecture, that galena 

 in these veins has been in some instances supplied by subli- 

 mation from below. I am. Gentlemen, yours, &c. 



Lowleyer-Alston, Jan. 13, 1829. H. L. PatTINSON. 



XXVI. On the Curvature ofSpirit-Levels. By J. Nixon, Esq. 

 To the Editors of the Philosophical Magazine and A?inals. 

 Gentlemen, 



SOME years ago I received from Mr. DoUond four ground 

 spirit-levels (unmounted), of which two served to replace 

 the much less sensible original levels of the horizon-sector al- 

 luded to in Phil. Mag. and Aaiiali, vol. iii. page J 90. The 



lubes 



