134 .Mr. cavendish’s Account of 
Where the impurities mixed with the air have any con fidfera- 
ble fmell, our fienfe of imelling may be able to difcover them, 
though the quantity is vaftly too fmall to phlogifticate the air 
in fuch a degree as to be perceived by the nitrous teft, even 
though thole impurities impart their phlogifton to the air very 
freely. For instance, the great and inftantaneous power of 
nitrous an* in phlogifticating common air is well known ; and 
vet ten ounce meafures of nitrous air, mixed with the air of a 
room upwards of twelve feet each way, is fufficient tq commu- 
nicate a h:rong fmell to it, though its efFedt in phlogifticating 
the air muft be utterly inlenfible to the niceft Eudiometer ; for 
that quantity of nitrous air is not more than the 140000th part 
of the air of the room, and therefore can hardly alter its teft 
by more than , ro ! . 6 ^ or __-4_ 0 th part. Liver of fulphur alfo 
phiogifticates the air very freely, and yet the air of a room 
will acquire a very ftrong fmell from a quantity of it vaftly 
too fmall to phlogifticate it in any fenfible degree. In like 
manner it is certain, that putrifying animal and vegetable fub- 
ftances, paint mixed with oil, and flower's, have a great tendency 
to phlogifticate the air ; and yet it has been found, that the 
air of an houfe of office, of a frefh painted room, and of a 
room in which fuch a number of flow r ers were kept as to be 
very difagreeable to many perfons, was not fenfibly more phlo- 
gifticated than common air. There is no reafon to fuppofe 
from thefe inftances, either that thefe fubftances have not 
much 'tendency to phlogifticate the air, or that nitrous air is 
not a true teft of its phlogiftication, as both thefe points have 
been fufficientlv proved by experiment ; it only ffiews, that 
our fenfe of fmelling can, in many cafes, perceive infinitely 
fmaller alterations in the purity of the air than can be per- 
3 ceived 
