121 A. L. Day and B. B. Sosman — 



arrange and manipulate, provided the furnace is well insulated 

 so that the temperature can be reached without difficulty. 

 Palladium strains the platinum resistance furnace near to its 

 limit of endurance on account of the high temperature, but 

 has the great convenience of not requiring a reducing atmos- 

 phere. Special pains need to be taken, however, in this case, 

 to protect the thermoelement from contamination. 



Nickel and cobalt were melted in an atmosphere of hydro- 

 gen which was made by electrolysis in a large glass and earthen- 

 ware generator, and purified by passage through potassium 

 pyrogallate and sulphuric acid. Just before the thermoele- 

 ment was introduced, the hydrogen was displaced by pure 

 nitrogen drawn from a steel tank in which it was stored under 

 pressure. The supply contained a trace of hydrogen and was, 

 therefore, purified by passing over hot copper oxide and 

 through calcium chloride and sulphuric acid. The extreme 

 lightness of this gas compared with the outside air (especially 

 when it is heated to 1450°) makes necessary special precau- 

 tions in order to keep out any trace of air. Furthermore, 

 hydrogen always caused contamination in the thermoelement, 

 wmich was not prevented even when the hydrogen was replaced 

 for a short time during the melting by pure nitrogen. Nickel 

 and cobalt are, therefore, not recommended for frequent use 

 in the calibration of thermoelements, if the two points, diop- 

 side and palladium (or diopside and anorthite), give a sufficient 

 calibration for the purpose in hand. 



The apparatus used for the melting points of nickel and 

 cobalt is shown in section in fig. 6. The top of the large 

 porcelain tube (Marquardt, glazed outside only) was closed by 

 a sliding cup of brass in which the thermoelement tube and 

 two others for introducing hydrogen were fastened by heat- 

 ing the cup and pouring in molten solder. The porcelain tube, 

 extended far enough out of the furnace to keep the brass cup 

 cool. A groove near the base of the cup carried a piece of 

 asbestos cord which made a gas-tight joint with the porcelain 

 tube and permitted the whole to be raised and lowered with- 

 out moving the crucible or opening the top of the tube. Two 

 diaframs of Marquardt porcelain above the crucible also pre- 

 vented any considerable radiation upward to the brass cup. 



In zinc, antimony, silver, gold, and copper, the thermoele- 

 ment was protected by a glazed Marquardt tube of 5 mm inside 

 and 8 mm outside diameter. In the case of antimony, the tube 

 was further protected by a thin tube of graphite which fitted 

 into the cover of the crucible. With diopside and anorthite, 

 some contamination from iridium in the furnace may take place, 

 but can be largely prevented by surrounding the tube with 

 pure platinum. A glazed Marquardt tube cannot be used in 



