Page:Outlines of Physical Chemistry - 1899.djvu/162

 144 OUTLINES OF PHYSICAL CHEMISTRY

that immediately after t 20 the descent of the mercury has become regular.

In the third period (after the reaction), the temperatures £ 21, t 2 2 ho arG re& d off, and from this we find that

radiation produces a fall of 20 ~ 30 degrees per interval of

twenty seconds.

The real maximum temperature is calculated as follows :

Mean temperature of the first period : t b.

Mean loss by radiation for each interval of twenty seconds of this period :

Mean temperature of the third period : £ 2 5« Mean loss by radiation during this period :


 * " io—

We can admit that the losses by radiation which corre- spond to successive intervals (20") are proportional (approxi- mately) to the initial temperatures of these intervals. We shall then have

A n : Ag = * n : £ 5 and A 26 : A 5 = t 2b : t 5f from which we get

^n-A.5 _ t n - t h ftnd A 26 — A 6 _ * 25 - h

Consequently,

(A n - Aft) : (A 26 _ Aft) = (t n - * 8 ) : (* 26 - t b ) and

a. = (*„ - * 6 ) *;* ~ f « + a s.

This equation gives us the cooling corresponding to the successive intervals of the principal period. For the

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