VOL. LXIX.] PHILOSOPHICAL TRANSACTIONS. SBQ 



ture for the escape of vapour, but not so as to admit air for the inflammation 

 of the sulphur. These being put into the fire, as soon as they were heated red- 

 hot, the sulphur in part escaped through the small hole, and as it passed through 

 burnt with a blue flame. The fire was increased to a suflicient degree to melt 

 the mass within; in the mean time the blue flame disappeared, which showed 

 that no more sulphur escaped. 



After having applied heat enough, as was supposed, to melt tlie mass, the 

 crucibles were removed from the fire, and being separated when cold, a regular 

 button-like mass was found in the crucible, of a dark lead colour both without 

 and within, brittle, and streaked on the inside, bearing to be cut with a knife, 

 exactly like the vitreous ore, which it in every way resembled. The whole mass 

 gained 20 grs. or -J^ in weight, which may be considered as the true weight of 

 the sulphur in this compound, as silver combines with sulphur in its metallic 

 form, without losing its inflammable air. Fifty troy grains of this compound 

 was powdered with difficulty, from its toughness, and boiled in nitrous acid 

 diluted with water; it dissolved with difficulty, leaving a very small quantity of a 

 light blackish powder, certainly not nearly a grain in weight. It appeared there- 

 fore, that the small portion of sulphur contained in the vitreous ore might have 

 been decomposed by the nitrous acid, and the alkali, or the heat, in the former 

 processes; and they concluded, that vitreous silver ore is a compound of silver 

 and sulphur, and when pure, that it contains between Q2 or 93 grs. of silver in 

 100. 



XXXIV. On some neiv Methods of suspending Magnetical Needles. By John 



Ingenhousz, Body Physician to their Imperial Majesties, and F. R. S. 



p. 537. 



The great utility which navigation derives from the use of compasses, has 

 been the principal reason, that so much labour has been bestowed by many 

 ingenious men in searching the best method of suspending magnetic needles, 

 and that some Academies of Sciences have proposed considerable premiums to 

 be given to the person who should succeed the best in this important object. It 

 has been, and is still, a general complaint, that such needles as were by their 

 size and figure susceptible of the greatest magnetic power, and which were 

 executed with the greatest exactness, and perfectly balanced, were, for this very 

 reason of their superior accuracy, so easily put in motion, that the slightest shaking 

 of the floor, occasioned by the observers walking in the room, communicates to 

 them such a great quivering motion as to drag them outof their direction, and to 

 render a considerable time requisite before they are again fixed in the true mag. 

 netical meridian. 



Since the late Dr. Knight has improved so greatly the method of communi- 



