468 Capt. W. A. Ross on Pyrology, or Fire Analysis. [June 20, 



twisted into a loop, which must be perfectly circular, and of a diameter 

 corresponding to the size of glass required. It is a pair of common cage- 

 maker's pliers with round but tapering legs ; only the right (or left) leg 

 should be graduated and figured, say, in tenths of an inch, to show the 

 diameter of the loop made on the other one. Neither of these instruments, 

 however, is to be understood as at all dispensing with the use of the assay 

 balance, of which a beautifully portable description is now made cheaply 

 at Freiberg ; it indeed is indispensable, and to be referred to when any 

 doubt is entertained. 



Roasting through Vlatinum foil. 



80. The cautions and directions against using the platinum which is sup- 

 plied as part of all pyrological apparatus, to be found in most chemical 

 works, are manifold and almost amusing. It would be better, if these 

 directions are to be followed, to have no platinum foil at all than to have it 

 and not use it; but in practice it will be found that there are comparatively 

 few substances which injure platinum foil when heated through it, to such an 

 extent that it cannot be advantageously used for months. The ore called 

 " stibnite " is one of these, but with care even galena may be thus inno- 

 cuously roasted. 



81. The foil, which should be thicker than the usual English kind, can 



be conveniently made into a small tray about 1*5 X 1 inch, and held, as in 

 fig. 7, with a pair of brass pliers having steel legs, the subject of examina- 

 tion being deposited as a paste (made on a slab with distilled water) on its^ 

 lower lip. The point of the pyrocone must then be applied to the back of 

 the tray opposite the substance, and on no account is it to be directed 

 upon its surface. 



