High, Temperatures. 187 



Attention should perhaps be called to the fact that in the 

 comparisons between these elements and the normal element, 

 different sections of the same curve are separated in particular 

 cases by considerable intervals of time so that the distribution 

 of temperature from junction to junction was not always the 

 same even through the observations of a single series. Small 

 consistent differences between " Obs." and " Calcul." may be 

 fairly attributed to this cause, though for the temperature 

 range 300° to 1150° when the gas thermometer was used, the 

 differences rarely exceed 1° ; above 1150° where the figures 

 are based upon an exterpolation of the formula for T a they are 

 sometimes larger, though nowhere exceeding 5°. 



5. Melting Points of Metals. 



To render the calibration of thermo elements independent of 

 the gas thermometer we have determined the melting points 

 of various metals lying between 300° and 1100°. Two 

 methods were used : According to the first, a short wire 

 (about l cm long) of the metal to be melted was introduced into 

 the hot junction of the thermo-element itself, and the thermo- 

 electric force at the moment of the melting and consequent 

 interruption of the circuit, observed. This method is simple 

 but leads easily to doubtful results if the melting point is at 

 all affected by the surrounding atmosphere, as is the case with 

 most of the metals which oxidize in air. The element also 

 becomes considerably shortened by the continual cutting off 

 of the drop of melted metal after the observations and renew- 

 ing the junction. 



By the second method a larger quantity of metal is melted 

 in a crucible and the thermo-element, protected by light porce- 

 lain tubes, inserted. When the heating is properly regulated 

 the beginning of the melting or freezing point is readily recog- 

 nizable as the temperature remains stationary for a considerable 

 length of time. In the following, the words " wire method " 

 and "crucible method " may serve to distinguish the two proc- 

 esses. 



For the latter method the apparatus was arranged as indi- 

 cated in fig. 3. A porcelain or graphite crucible is contained 

 within a short fire-clay tube carrying a coil of bare nickel wire 

 whose separate turns were insulated by smearing with clay. 

 The whole is protected against loss of heat by a layer of loose 

 asbestos A and a thick protecting tube also of fire-clay. The 

 wires of the thermo element are insulated from each other by 

 means of thin porcelain tubes and from the molten metal by a 

 somewhat thicker tube of the same material, 5 mm in inside 

 diameter and l-o 111 ™ in thickness, which dipped at least 4 cm into 



Am. Jour. Sci. — Fourth Series, Vol. X, No. 57.— September, 1900. 

 13 



