463 
Nutrition oj Vegetables . 
length determined on for each stretch, and then give it the re- 
quired twist. Previous to your returning the swing for winding 
up the yam, gently turn the wheel, a very small distance back- 
ward, to unwind the yarn a little way from the spindle, then tread 
on the foot piece which will cause the traverse rod to distribute 
the yarn down the spindle so as to form your (torn) you are 
returning the swing with one hand, and the spindle with the other, 
to wind up the stretch that had been spun. When the foot is 
raised from the foot-piece, the pea, or small balance weight from 
the roller D, will return the traverse rod to its place.— Should a 
strand break in pushing out the swing, do not stop to mend it un- 
til you have returned the swing, and then tye it— A little prac- 
tice will render the use of the machine familiar and easv— A 
child may be employed to piece the rolls. 
NUTRITION OF VEGETABLES. 
( Concluded from fiage 303 . ) 
These experiments show the extreme facility, with which thfc 
oxydes of lead are reduced, and the obstacle that carbonic acid 
opposes to this reduction. 
As these first attempts did not afford me the result I sought, 
I availed myself of an old experiment of Huyghens, who, in 1672, 
put some earth into a bottle, corked it up, and found it produce 
such a quantity of plants, as almost to fill the bottle, without hav- 
ing had any fresh air admitted to it. Accordingly I procured six 
large flint bottles, most of which were square t: filled them in part 
with very fine white sand, which I deprived of all calcareous earth 
by washing with weak muriatic acid ; and moistened this with dis- 
tilled water. The remainder of the bottle was filled with atmos- 
pheric air freed from carbonic acid. 
In these bottles having sowed 460 seeds of white mustard, I 
closed them very accurately, and placed them a few inches deep 
in a moist soil. Vegetation soon commenced, and considerable 
verdure was produced.* After six weeks growth my plants were 
* It may be supposed, that these seeds did not germinate with as much 
vigour, as if in the open air. This however 1 do not think must be asc^bee! 
to the want of oxygen ; for by trial of the air with a sulphuret before and 
