PROPERTIES OP IRON AT A HIGH TEMPERATURE. 
4G5 
distance between the two straight parts of the curve is 810 seconds. It follows that 
the heat liberated in recalescence of this sample is 173 times the heat liberated when 
the iron falls in temperature 1° C. With the same sample, I have also observed 
an ascending curve of temperature. There is, in this case, no reduction of temperature 
at tlie point of recalescence, but there is a very substantial reduction in the rate at 
which the temperature rises.'" 
A similar experiment was made with a sample of wrought iron substantially 
the same as the wrought iron ring first experimented upon. The result is shown in 
Curve XXXIX. It will be seen that there is a great pause in the descent of this 
curve at a temperatui-e of 820° C., but that the curve does not sensibly rise. This 
shows why soft iron apparently does not recalesce. Determining the heat liberated in 
the same way as befoi e, we find the temperature falling after the bend in the curve at 
the rate of 0°'217 C. per second. The distance between the two straight parts is 960 
seconds. Hence, heat liberated in recalescence is 208 times the heat liberated when 
the iron falls 1° C. in temperature. The temperature at which a sample ordered a.t the 
same time and place ceased to be magnetic was 780° C. Comparing this result with 
that for hard steel, we see that the quantity of heat liberated is substantially the saiue, 
but that in the case of the soft iron there is no material rise of temperature.t 
[* Note added 2nd July, 1889.—Some remarks of Mr. Tomlinson’s suggested that it might be 
possible that there would be no recalescence if the iron were heated but little above the critical point. 
To test this, I repeated the experiment, beating the sample to 765° C., very little above the critical 
jioint. Curve XXXVIIIa. shows the result. From this it will be seen that the phenomenon is sub¬ 
stantially the same whether the sample is heated to 988° C. or to 765° C.] 
[t Note added 2nd July, 1889.—In order to complete the proof of the connexion of recalescence and 
the disappearance of magnetism, a block of manganese steel was tried in exactly the same way as the 
blocks of hard steel and of iron. The result is shown in Curve XL., from which it will he seen there is 
no more bend in the curve than would he accounted for by the presence of a small quantity of magnetic 
iron, such a quantity as one would expect from the magnetic results, supposing the true alloy of man¬ 
ganese and iron to be absolutely non-magnetic.] 
3 o 
MDCCCLXXXIX.-A. 
