HEAT OF EVAPORATION OF WATER. 293 
investigation on this point, and I am confident that the values of Q, given in the 
following table are correct to better than 1 in 50, at temperatures 30° and 40°, although 
T am less certain about the values at 20° and 50° C.* The latter, however, are not 
required for the purposes of this paper, except in so far as they affect the specific heats 
of the oil in Table ITI. 
Taste VI.—Thermal grams per sec. (Q,) at rate (7) 5°300 revolutions per sec. 


| 6. Q.. e —Hies 
50 ‘00235 298 x 1078 
40 -00466 590 x 10-8 
30 ‘00665 843 x 10-8 
20 -00834 1056 x 10-8 



Let Q’, be the thermal grams per second due to a rate 7. 
Then 
Qifrt = Qfrt = b, 
therefore 
Y.-—Q, =k(rt— ry, 
therefore 
OF SOT (Gr Sine aie te alt ek Gs) 
Hence 
Temperature 40°, then Q’, = ‘00466 + (7, — 789) x ‘0000059. 
ee 30m as Q’, = 00665 + (ae! — 789) x 0000084. 
I do not, of course, suppose that Q, = fr* is the exact relation. I have already 
indicated that 7* was too small at high, and too great at low temperatures. It must 
be remembered, however, that the variations in 7 were small, and thus the relation is 
sufficiently close for the correction of such variations as occurred during these 
experiments. 
If we assume that the work done (for a given value of r) is proportional to the 
viscosity, the values of Q, denote how great a change in viscosity is produced by 
raising the temperature from 20° to 50°. I repeat, however, that the values at 20° 
and 50° must be regarded with suspicion. 
* I have no corroborative experiment (by the former method) at 20°, and only one at 50° (see 
Appendix IT.). 
