128 
DR. P. F. FKANKLAND ON THE QUANTITATIVE ESTIMATION OF 
In order to secure this relationship between the plugs (a) and (b), the former is 
constructed of a small quantity either of ordinary glass-wool or of glass-wool which 
has been previously coated, with cane-sugar by soaking it in a saturated solution of 
the latter and then drying. The plug (6), on the other hand, is constructed of fine 
sugar or glass-powder (passed through sieve of 40 meshes to the linear inch), supported 
in front and behind by a layer of glass-wool, either plain, or coated with sugar as above. 
Each of these plugs is about the size of a pea, and with a little practice the packing- 
can be easily arranged to give the requisite degree of imperviousness. 
Plug (c) is simply a piece of'cotton wool, loosely packed, and serves to protect the 
back of plug (b) from any chance contamination. 
The control tubes, which are exposed during an experiment, but through w T hich no 
air is aspirated, are similarly constructed, with the exception that they have no plug (6). 
The tubes thus fitted are sterilised by being heated on 3-4 successive days, for 
several hours each day, to a temperature of 110°C. in the case of those containing 
sugar, to 160° C. in the case of those which only contain glass plugs. 
A number of tubes may conveniently be sterilised at one time in a tin box, or in a 
piece of wide glass tubing, sealed at one end, and fitted with a plug or cork at the 
other. In this manner the tubes can be transported without fear of contamination 
to the place where the experiment is to be performed. 
Fig. 2. 
2. Collection of the Sample of Air .—The sterilised tube, prepared as above 
described, is carefully taken from the sterile case, and is only handled by its 
extremity (B). The latter is now attached by means of a piece of stout indiarubber 
tubing to a piece of lead tubing about 10 feet in length, which is clamped at this end 
to a retort-stand or other convenient vertical support, whilst the other extremity of 
the lead tube is attached to a T~pi ece by which it is connected, on the one hand, 
with an exhausting syringe, and on the other with a mercury pressure gauge, both 
syringe and gauge being mounted on a rigid support placed upon the ground. 
