18 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 

 Y§ inch in diameter, that of the remainder of it is ^. 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 3G . 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 b} r 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 eacli 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. 



