242 PROCEEDINGS OF THE AMERICAN ACADEMY. 



in general agree. With too rapid rates of heating or cooling, they 

 are likely to show an erroneous disagreement. Under favorable con- 

 ditions, namely, with the galvanometer in a place free from jarring, 

 and with a steady air-blast of quite sufficient capacity, this method 

 yields perfectly good results, although the inexperienced observer will 

 generally miss the reading on the first one or two trials. But in 

 most places, notably in connection with industrial plants, it is not in- 

 frequently difficult or impossible to secure the necessary steadiness of 

 support or of blast. Failing these, the stopping point sought is very 

 likely to be so masked by irregularities in the motion of the spot as 

 to introduce much uncertainty into readings, if not entirely to prevent 

 satisfactory calibration by this method. 



Another way is to have the two thermal wires held together at 

 the ends merely by the wrapping of gold, etc., and under slight ten- 

 sion, so that as soon as the metal melts the wires will draw apart and 

 open the circuit. The spot will then reach a highest point correspond- 

 ing to the melting point, and then suddenly drop to zero. In prac- 

 tice this method, although convenient in some cases, has been found 

 not to yield satisfactory results on the whole. 



With some metals, particularly those melting below gold, the author 

 has found the following arrangement to work well, being more rapid 

 and under better control. A small crucible of fire-clay, lA or 2 inches 

 long, and ^ to j^- inch inside diameter, with straight sides and a flat 

 bottom, is employed.* Into this is inserted the clay tube carrying the 

 wires, a packing of asbestos being used around it, if it does not pretty 

 well fit the crucible. The junction remains free about half an inch 

 from the bottom and not touching the sides. The crucible is then 

 gradually heated in the flame of the blast lamp, and the stopping 

 point observed as before. 



Platinum. — For this we depend on the direct fusion of the plat- 

 inum wire of the couple just at the junction. f A convenient way is to 

 fuse the ends together, then to bend the wires so that the two lie 

 closely side by side, and are nearly straight, but not touching. Then 

 lay the end on a smooth surface of quicklime. A small flame from 

 the oxyhydrogen blowpipe is then directed upon the junction. The 

 globule at the end will fuse, and may gradually work up along the 



* Made to order by Hall and Sons, Tonawonda St., Buffalo, N. Y. 



t It may be of interest to others, as it was to the writer, to learn that the firm 

 of Heraeus of Hannover, Germany, whicli has made platinum of exceptional 

 purity for the Reiclisanstalt, has an agency in New York, Charles Englehard, 41 

 Cortland St., N. Y. 



