Download Page 45a of James Watt`s Laboratory Notebook

Reverse of page 44 of James Watt’s Laboratory Notebook
Distillation in vacuo
I suppose to be = to 2 ounces of  (that is to 2/3) of its bulk of water) An error
was committed on the other page in computing the quantity of heat given by
the tin cone by its weight instead of it Bulk The calculations should stand as
follows:
130oz 6dr of water =
28oz tinned Iron =
to [-] ------the 2 oz water
132.6
which is = to grains
63620
x by degrees gained
9o
572580
subtract heat given by cone
143 x 72 = 10296 ÷ by 2/3
= 7000
÷ by the weight of
565580
condensed  in cone -----534
gives 1059 Latent heat + 62 heat retained = 1121 sum of sensible and latent
heat
NB no allowance is made for water adhering to Cone because it was equally
wet at the beginning of experiment and I even suspect that there was some
water condensed in it before put into refrigeratory.
Page 45a of James Watt’s Laboratory Notebook
April 1814 Observations on the experiments on Latent heat p.38 to 42.
These experiments were made with great care, but two material errors
were committed in the mode of calculating them. The first was the assuming
the avoir dupois ounce at 432 grains; whereas it contains 437½
This was perceived in the course of the experiments & the 9th 10th &
11th were calculated properly in that respect, but the others remained
uncorrected, till this time
The second error consisted in adding the condensed Steam to the
weight of the cold water and after multiplying that sum by the heat gained,
adding & dividing by the weight of the condensed Steam, adding the degrees
of heat of the cold water, in order to find the total sensible and Latent heats.
Whereas the weight of the cold water alone should be x by the heat
gained and divided by the weight of the condensed steam, to which should be
added the heat of the hot water, to give the total Sensible and Latent heat,
from which if the sensible heat of boiling water = 212 be deducted the
remainder is the latent heat, as is directed in p.38. As it happened however
these errors nearly balanced one another so that the results did not differ
materially.
On looking over these experiments this year on the occasion of
correcting Dr Robison’s article on Steam & Steam Engines
[continued on reverse of page 45a]