MEASUREMENT OF TEMPERATURE. 
201 
Comparison of Platinum and Iron. 
The comparison of platinum and iron is interesting because iron behaves so 
peculiarly. A considerable number of comparisons were made by different methods ; 
the most accurate is the last series, "VI., for which the same apparatus was used as in 
the comparison of two platinum wires. All the series, however, agree with each 
other as nearly as can be expected, considering the different modes of treatment, and 
that ordinary commercial soft iron wire was used. 
The first experiments were made at the beginning of November, 1885, with unan¬ 
nealed iron wire wound side by side with platinum on a strip of asbestos board, and 
heated in an air bath up to 200° C., a mercury thermometer being used to show when 
the temperature was steady. 
The following simultaneous values of the resistances were observed :— 
Iron . 2-254 1-890 1-449 1-075 
Platinum. 1-700 1-536 1-294 1-055 
Temperature, pt .. .„ 202'0 01547 857 16'0 
Afterwards the wire was partially annealed, and the same coil was heated in 
paraffin in the same air bath, with the following results :— 
Iron . 2-250 1-941 1-278 1743 1-000 0 
Platinum. 1-701 1-561 1-194 P105 1 000 lSeries II. 
Temperature, pt .. .. 202'2 161*8 56‘0 307 In ice J 
In order to command higher temperatures, a new comparison coil was made and 
enclosed in an exhausted tube, to prevent oxidation of the iron, which was first 
carbonised by annealing in coal gas ; the whole was heated in an iron tube by a 
regulated gas furnace. The following observations were taken 
Iron observed .. .. 6-015 3704 1-5170 2-3840 3'2414'j 
Platinum. 2‘8264 2’225 P3388 17713 2-0807 V Series III. 
Temperature, pt .. .. 528-0 354-1 98’0 223-2 312-1 J 
To investigate more particularly the effect of annealing, another comparison coil 
was wound with the iron wire unannealed, and observations were taken with it up to 
100° C., with the following results :— 
Order of observation .. 2 3 4 5 1 
Resistance of iron .. 1-5330 1-4114 1-2486 1-0704 P0688"] 
Resistance of platinum . . 1-3463 1 2732 1-1721 1-0507 1-0495 l Series IV. 
Temperature, pt .. .. 100"09 79"0 49’6 15'0 14"6 J 
Before annealing, the resistances at 0° C. were:—Resistance of iron, 5'001 ohms; 
resistance of platinum, 9'887. After annealing, resistance of iron, 5'557 ohms; 
MDCCCLXXXVII.-A. 2 D 
^Series I. 
