122 Scientific Proceedings, Royal Dublin Society. 
of greater capacity, with the same coating. In practice we found 
it somewhat troublesome to coat the vessels properly, as a rather 
thick layer of the wax is necessary, or it becomes detached from 
the glass in course of time. This difficulty is avoided by proceed- - 
ing as follows :— 
Ordinary (white) paraffin wax is melted and allowed to cool 
until near its solidifying point. It is ther poured into the cold 
vessel, and the latter rolled round until a uniform and sufficiently 
thick coating is obtained over all parts. A little practice is neces- 
sary to effect this properly, but the operation is not difficult.* 
In our earlier determinations the titration of the excess of 
absorbent was performed, as we have said, within the receiving 
vessels, which were closed during the period of absorption by 
vaselined stoppers or india-rubber corks; but later, when the 
absorbent was drawn off into a vacuous vessel and there titrated, 
the receiving vessels were fitted as shown in the subjoined 
diagram. 
Two glass tubes pass through either an india- 
rubber cork, or an ordinary cork well soaked in 
hot paraffin wax. These were closed when neces- 
sary by plugs, consisting of short glass rods 
attached to pieces of india-rubber tubing. 
To fill one of these receivers with a sample of 
air, the method of exhaustion was employed, the 
operator being at a sufficient distance from the 
collecting area to avoid the possibility of breath 
contamination. For this purpose an air-pump, or 
rather exhausting syringe, was attached to one 
end of an india-rubber tube, about 12 feet long, 
while the other end of this tube was connected 
with I. or II. of the receiver. The pump removed 
about 200 cc. of air at each stroke, and, as a rule, we gave 100 
strokes in each filling, so that 20 litres of air passed through the 
recelver—a quantity we deemed more than sufficient to ensure 
complete displacement of that which was originally present by the 
Eirg. 1. 
Paraffined Receiving 
Vessel. 
1The receivers thus coated should be left for some time before their capacity is 
ascertained, otherwise, on filling with water for that purpose, the paraffin is liable to 
crack. 
