PYttOMETER OF PLATINA. 



89 



VII. 



Account of the Pyrometer of Platina. By Citiaen Guyton.* 



t^ITIZEN GUYTON prefented an inftrument to the fit- Pyrometer for 

 ting of the French National Inftitute of the 26th Floreal laft, fiftj^g'^ akver 

 intended to meafure the higheft degrees of heat of our furnaces, of platina moved 



It confifts of a rod or plate of platina placed horizontally in ^y f^arTttr 

 a groove formed in a cake of hardened white clay. This plate fame metal; the 

 is fupported at one of its extremities on the part of the mafs whole Ijeing fupr 



1- 1 1 rr • /I ported on a mals 



which termmates the groove; the other end preiies agamlt a of baked clay. 



bended lever, whofe longeft arm forms an index to a graduated -^^ isgo-vemediy 



arc ; fo that the change of poiition of this index indicates ^^^ the expanfiom of 



expanfion produced on the plate of metal by the heat. pttery gndpla- 



The cake of clay having been highly baked, leaves no caufe [)gfci.jp(^on. 

 to apprehend any contradtion ; and the expanfion vv'hich may 

 take place during the ignition will only affedl the very fmall 

 diftance between the axis of motion of the index and the point 

 of conta6l of the plate, that is to fay, in fuch a manner as ra- 

 ther to diminifli theefFed than to increafe it. 



All the parts of this inftrument being of platina, neither fu- 

 fion nor oxidation are to be apprehended. 



With refped to its dimenfions, the author conceives that in Dlmen/ions. 

 order to render the ufe of it commodious and accurate, they 

 (hould be reduced to fuch as may be necefTary to obtain fenfible 

 variations ; it will then be rendered commodious by the facility 

 with which it may be placed under a muffle or an inverted 

 crucible, &c. and accurate, becaufe the probabilities of any 

 accidental inequalities of the heat will be diminiflied, which it 

 is impoffible to avoid to a certain extent, even in the midft qi 

 2l large mafs of fire. 



The variations will be fufficiently perceptible, if we can not Degree of accu- 

 only eftimate, but corredly determine expanfions of the 200th ^^^f' 

 part of a millimetre (about the 5000th part of an inch,) thefe 

 the author obtains by the proportions of the inftrument which 

 he has hinifelf adopted. 



The rod or plate of expanfion is 45 millimetres (one inch Dimenfions of 

 and three quarters) in length, 5 in width (one fifth of an inch)^^^ P""' 

 and 2 in thicknefs (one thirteenth of an inch.) 



* Annates dgCh'miey No. 138. XLVJ. 276. 



The 



