Chap. 2.] Electrical Machines. 321 



conductor, and thefe points fhould be placed within its 

 atmofphere. 



Sometimes the filk will adhere fo ftrongly to the 

 cylinder, when zinc amalgam is ufed, as to render ic 

 very difficult to turn j this may be obviated by rub- 

 bing a fmall quantity of aurum mufivum, or a little 

 whiting, over the filk, when it is wiped clean *. 



There are now in ufe two kinds of amalgam : One 

 is made of quickfilver five parts, zinc one part, which 

 are melted together with a fmall quantity of bee's - 

 wax; the other is the aurum mufivum of the fhops. 

 Before either of thefe will adhere clofely to the filk it 

 is neceflary to greafe it, to wipe off the fuperfluous 

 greafe, and then fpread the amalgam. 



One property of the electric fluid it will be neceflary 



The following direftions of Mr. Adams, relative to exciting 

 the machine, will be ufeful to the experimentalift : 



' To excite your machine, clean the cylinder, and wipe the 

 filk. 



' Greafe the cylinder by turning it againft a greafy leather, till 

 it is uniformly obfcured. The tallow of a candle may be ufed. 



' Turn the cylinder till the filk flap has wiped off fo much of 

 the greafe, as to render it femi-tranfparent. 



' Put fome amalgam on a piece of leather, and fpread it well, 

 fo that it may be uniformly bright; apply this againfl the turning 

 cylinder, the friclion will immediately increafe, and the leather 

 muft not be removed until it ceafes to become greater. 



' Remove the leather, and the aftion of the machine will be 

 very llrong. 



The preffure of the cufhion cannot be too fmall, when the ex- 

 citation is properly made. 



' The amalgam is that of Dr. Higgins, compofed of zinc and 

 mercury ; if a little mercury be added to melted zinc, it renders it 

 eafily pulverable, and more mercury may be added to the powder, 

 to make a very foft amalgam. It is apt to cryftallize by jepofe, 

 which fccms in fome meafure to be prevented by triturating it 

 with a fmall proportion of greafe : and it i.s always of advantage 

 to triturate it before ufing.' 



VOL. I. Y to 



