ic8 Sir Benjamin Thompson's Experiments 
Surfaces. It appears likewife, from the two laft experiments, 
that the air which is furnifhed in the beginning of the experi- 
ment, or when the water is firft expofed to the action of the 
fun’s rays, is neither fo good, nor in lo great abundance, as 
afterwards, at a more advanced period ; and that it totally ceafes 
to be produced after a certain time. 
To afcertain, with greater precition, the qualities of the air 
furnifhed at different periods of the experiment, or rather the 
period when the water begins to give good air p, and alfo to- 
determine the relative quantities and qualities of the airs pro- 
duced in the experiments with raw filk, and in tbofe with, 
poplar cotton, I made the following experiments. 
Experiment N° 17. 
A globe, about 44 inches in diameter, containing juft 46 
cubic inches, being filled in the evening with frefh fpring wa- 
ter, and 30 grains of raw lilk which had been previoufly 
wafhed thoroughly to free it of air and the remains of former : 
experiments, and being expofed the next day in- my window, 
the weather being cold and cloudy, with not more than 1 hour 
of funfhine, | of a cubic inch of air was produced, which, 
proved with nitrous air, gave in -p 2«= 1,86, or 114. 
The two following days, the weather being clear and mode- 
rately warm, 3-3 cubic inches of air were produced, which, 
proved with nitrous air, gave 1*74-372= 1,14, or 296. 
Experiment N° 1 8 . 
The globe having been again filled with frefh fpring 
water, and the fame filk which had ferved in the laft experi- 
ment, after 2 nights, and 1 day of about 4 hours fun, it had 
furniftied 1^ cubic inch of air, whofe quality was ia+2nzz 
or J 97* 
The 
