191 
covered) showed much more ; the back of a chair showed 
ammonia, when rubbed with a common duster, very little. 
It seemed clear that ammonia stuck to everything. 
If, then, ammonia were everywhere, the conclusion seemed 
to be that it was not at all necessary to do as I had been 
doing, namely, wash the air so laboriously; it would be 
quite sufficient to suspend a piece of glass and allow the 
ammonia to settle upon it. For this purpose small flasks 
were hung in various parts of the laboratory, and they were 
examined daily. The flasks would hold about 6 ounces of 
liquid, but they were empty, and the outer surface was 
washed with pure water by means of a spray bottle ; it was 
done rapidly, and not above 20 cc., two-thirds of an ounce, of 
water was used. This was tested for ammonia at once with 
the Nessler solution. The second washing produced no 
appearance of ammonia, done immediately. Ammonia could 
be observed after an hour and a half’s exposure at any 
rate, but I do not know the shortest period. The results 
of the washings were as follows. They are the average of 
34 experiments for some, and 17 for others, in all 238 
experiments. 
Height Ammonia. Height Ammonia, 
from floor. from floor. 
Ft. In. Mgms. Ft. In. Mgms. 
Front laboratory 7 3 ... ‘013 ... 4 2 ... "019 
2nd landing 6 0 ... ’032 
Balance room 5 1 . . *015 ... 0 8 ... '009 
1st landing 4 10 ... ’007 
Back laboratory 4 5 ... *010 ... 0 6 ... ’010 
Entrance lobby 6 5 ... *007 
Office 4 7 ... *003 
Back yard 4 8 ... *036 ... 0 7 ... ‘042 
Back closet 2 3 ... ’105 
Midden ’572 
The first three belonging to the working laboratory are 
not very regular, as we might suppose, but they never rise 
very high, nor do they sink to the lowest. The rest, except 
the second, keep a remarkable similarity, and the differences 
are very great. In the second there is a disturbance caused 
