Nitrogen Thermometer from Zinc to Palladium. 127 



between the melting points. No freezing point can be obtained 

 as the mineral undercook considerably. The charge used was 

 3 grams. 



Nickel. — A sample of specially purified electrolytic nickel 

 was obtained from Kahlbanm. The analysis showed less than 

 0'2 per cent total impurities. Care must be taken in the case 

 of nickel that no oxide forms, as a fairly sharp break can be 

 observed about 10° below the melting point, which may repre- 

 sent the eutectic of nickel and nickel oxide. This break disap- 

 peared when the nitrogen was replaced for a few minutes by 

 hydrogen. This lower point may easily be mistaken for the 

 melting point of the metal, and this mistake seems to have 

 occurred in several of the published determinations of the 

 melting point of nickel. Nickel absorbs hydrogen aud possibly 

 also nitrogen, and after cooling frequently showed excrescences 

 and signs of "spitting" such as occur with silver in air. 



Cobalt. — Kahlbaum's purest cobalt was used, containing less 

 than 0*05 per cent total impurity. It was in the form of fine 

 black powder, which was compressed into blocks for conveni- 

 ence in handling. The results obtained were not quite as satis- 

 factory as with nickel on account of the higher temperature 

 and more rapid contamination of the thermoelement. The ab- 

 sorption of gases seemed to be less than was the case with nickel. 



Samples of Eimer and Amend's "98 to 99 per cent pure" 

 nickel and cobalt were also tried. The difference between the 

 two samples of nickel was not greater than the uncertainty 

 in the melting point caused by contamination of the ther- 

 moelement. The "98-99 per cent pure" cobalt melted about 

 3*5° lower than the pure sample. Since the impurities in 

 nickel are usually chiefly iron and cobalt, and those of cobalt 

 are chiefly iron and nickel, and since the melting points of all 

 three are close together, the melting points of the slightly 

 impure metals can not be expected to lie far from those of the 

 pure metals. 



Anorthite. — Only one preparation of anorthite was used, 

 made by G. A. Rankin 1909. The charge was about 3 grams. 

 The melting point is not quite as sharp as that of diopside. 

 Only the melting point can be obtained, as the mineral under- 

 cook considerably ; it may even cool to glass without crystal- 

 lization, in which case of course no melting point will be 

 obtained on the following heating. 



Palladium. — About 350 grams of pure palladium, in the 

 form of sheet, was loaned to us by Dr. Heraeus. It melts and 

 freezes quite sharply, making an excellent substance for a fixed 

 thermometric point. The greatest uncertainty is caused by the 

 vaporization of the metal and consequent contamination of the 

 thermoelement wire. The charge used weighed 128-210 grams 



