336 



Scientific Proceedings, Royal Dublin Society. 



Hence the pressure in the air spaces after resetting tlie manometer will 

 be less than that existing at the start by a 

 quantity dependent on the ratio of the 

 volume of gas absorbed to the combined 

 volume of the two air spaces. By making 

 the latter large this quantity can be made 

 very small at will. 



III. — Description of Apparatus. 



The apparatus which was devised on 

 this principle is shown diagramniatically in 



fig- 2. 



It consists of two cylindrical glass ves- 

 sels about 30 mm. in diameter, which are 

 connected to two branches of a three-way 

 tap. The lower vessel is of such a size as to 

 contain a suitable volume (say 100 c.c.) of 

 the liquid to be tested, and still leave room 

 for an air space of about 50 c.c. ; the upper 

 vessel has also a capacity of about 50 c.c. 

 The three-way tap allows of the two air 

 spaces being connected through the mano- 

 meter, or directly, according to its position. 

 Hence, when an absorption has taken place, 

 the manometer can be reset to zero by suit- 

 ably turning the tap. 



The whole apparatus, including the 

 manometer, is enclosed in a cylindrical 

 water-jacket, through which water is cir- 

 culated from a thermostat. The handle of 

 the three-way tap projects through a hole 

 blown in this water-jacket, the joint being 

 kept water-tight by means of a rubber 

 diaphragm. The water-jacket is closed at 

 each end by flanges, which may be made of 

 brass, tin, or ebonite, according to the pur- 

 pose for which the apparatus is to be used. 



The stirrer passes through a long sleeve 

 in the lower flange, and is provided with 

 two conical surfaces, one of which can be 



Fig. 2. 



