142 
THE ART OF REARING 
not in the grate ; and however grateful the odour 
may be, it will consume a part of the respirable or 
vital air contained in the room, and consequently 
must injure the air. 
2d. The vegetable substance in burning will 
consume vital air, and in return exhales a mephitic 
gas, most noxious to respiration, and which may 
kill the silk-worms very soon. 
3d. Vinegar even, when poured upon hot sur- 
faces, is decomposed, and emits a mephitic gas, 
which augments that which previously existed. 
These evils which I have been relating may be 
mitigated perhaps by a concourse of three circum- 
stances. 
1st. The vegetable substances are sometimes 
burnt in the grate, or fire-place, instead of the 
centre of the room : in which case the effect will 
be like that produced when we make a blaze. 
2d. At other times, when, the vegetable sub- 
stances are set on fire, the apertures of the apart- 
ments are all well set open, and the motion of the 
exterior and interior air expels some parts of the 
vitiated air, and diminishes the evil that might 
have injured the silk-worms, had the rooms been 
shut up. 
3d. The surfaces upon which the vinegar is pour- 
ed are sometimes only warmed, and not red-hot, 
which prevents the decomposition of the vinegar. 
