1s PROFESSOR CONNELL ON A 
This, during three months’ observations, I have found to be sufficient for general 
use; but an extreme case occurring, when, after reducing the temperature be- 
low 20°, no dew occurred, I thought of a method of increasing the effect without 
having recourse to any augmentation of the size of the syringe. This was to have 
a collar of ivory introduced between the little bottle and the syringe, so as to cut 
off entirely metallic communication between them. The passage into the bottle 
of the heat generated during the motion of the piston, would thus be pre- 
vented, and the cold produced by the evaporation of the ether would be enabled 
to take full effect. This idea was carried into execution, by constructing of ivory 
the extremity N of the syringe carrying the terminal valve. The aperture 
in the portion of this ivory piece to which the valve is attached is at least 
7; inch in diameter, that of the remainder of it is 4. This ivory piece screws into 
the brass passage which conducts into the neck of the bottle. Since this change 
was effected, I have experienced little difficulty in producing the necessary 
cold, even in a very dry atmosphere, and have obtained it even as low as 8 F., 
with the external air at 36°. There is one point, however, which requires atten- 
tion in the use of this ivory valve-piece,—to avoid any considerable force either in 
screwing or in unscrewing it, as its fracture is risked. Hence we ought to be 
particularly on our guard against this screw getting fixed, either by being over- 
screwed, or by remaining too long unmoved. Indeed the safer way is, always 
after using the instrument, to loosen this screw lightly, and leave it so till next 
observation, and then tighten it again; and if it should happen to get fixed, to 
wrap it round with cotton, moisten the cotton well with olive-oil, and leave it in 
this state for a couple of days, when it will admit of being unscrewed without 
injury. If necessary, a projecting screw of brass might be attached to the lateral 
passage into the bottle, and fit into the ivory valve-piece. 
At a much earlier period of the trial, a difficulty occurred as to the valves of 
the syringe. These were at first constructed of the usual oiled silk. But it was 
soon found that the ethereal vapour acted on them, and impaired their energy. 
Vulcanized Indian-rubber was then tried, but, as might have been foreseen, from 
the solvent action of ether on caoutchouc, this material, although it stood better 
than the oiled silk, was also affected. I then thought that it would have been ne- 
cessary to have had recourse to metallic valves, when Mr ALEXANDER Kemp sug- 
gested the employment of goldbeaters’ leaf. This suggestion, contrary perhaps to 
what might at first have been expected, has hitherto proved quite successful ; and 
I have now been daily using, for three months, two syringes, the valves of which 
are made of this substance, without any material diminution of their action.* 
I had at first thought of holding the apparatus simply in the hand during its 
* In constructing each valve, four folds of the leaf are employed. Should the valves become 
impaired by use, they may easily be renewed, and the leather of the piston may also in time require 
renewal also, 
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