434 Dr. J. A. Harker on the Specific 



furnace to the calorimeter. Since in these experiments 

 the specimen was permitted to fall freely under gravity, 

 and the vertical distance from the normal position of the 

 specimen in the furnace to the surface of the calorimeter 

 water was only about 20 cm., it is obvious that the un- 

 certainty from this source is not great, even at the highest 

 temperatures. 



In the later series of , experiments, where it was found 

 possible to push the temperatures up above the safe working 

 limit for accurate platinum thermometry, thermocouples were 

 substituted for the thermometers. In the later experiments 

 with the couples, to ensure accuracy the end of the thin 

 steel tube enclosing the couple was inserted into a block of 

 iron of similar shape and size to the sample. 



Above 1000° C, however, prolonged exposure of the 

 couple to contact with iron direct is not permissible in the 

 oxidizing atmosphere of a furnace arranged vertically as in 

 this case. The thin steel tube is therefore to be replaced by 

 one of porcelain. 



Above about 800° C. it was found that the oxidation of 

 the specimen of iron in the furnace, and its disintegration 

 when dropped suddenly into the calorimeter water, was so 

 rapid as to introduce appreciable uncertainty into the experi- 

 ments, and, indeed, at temperatures not much higher it was 

 possible by prolonged exposure to transform the whole of a 

 small piece of the same iron into oxide. A number of 

 experiments were tried employing various means to prevent, 

 or at least retard, this action, among others gilding the 

 specimen by several different processes. Although by some 

 of these it appeared possible to considerably moderate the 

 oxidation, yet it was found that the sudden cooling always 

 detached the surface layer with its protecting covering, when 

 the whole was plunged directly into water. For work at the 

 higher ranges it was obvious therefore that a sheath of some 

 kind such as that used by Pionchon was necessary. A 

 thin tube of fused quartz will stand plunging suddenly into 

 water when at a fair red heat, but experiments showed that 

 when enclosing a cylinder of iron, even when this is separated 

 from it by a thin layer of inert material, the tube almost 

 invariably breaks up, when dropped directly into cold 

 water. 



The following modification of the process was then tried : — 

 Instead of allowing the iron to fall directly into the water, it 

 was caught in a vertical funnel-shaped tube of the form shown 

 in fig. 2. A pad of asbestos- wool on the bottom of the 

 tube was arranged to break the fall. The whole of the 



