( 639 ) 



through which water at constant temperature flows from the tliermo- 

 stat described in Comm. n\ 70 III May '01 (see ^«^ «n PI. II. fig. 1). 

 Uniformity of temperature is also assisted by the movement of the 

 stirrer on to which tiie thermometer Th is fixed. 



The ring Eqo together with the bottom plate is soldered to the case 

 Eao Ji-nd is large enough for the measuring vessel to be put (liroiigh 

 it. The closing plate J^c is made fast to the measuring vessel and is 

 so arranged, that it can easily be made watertight and that it can 

 bear the weight of the Avhole mass of mercury when the tube is 

 full without any danger to the glass as long at least as it is not 

 displaced from its vertical position. The closing plate with flange and 

 packing is pressed against the ring /^g at the bottom of Ua by 

 the screw L,.^. The different parts Avill be seen by an inspection 

 of PI. II fig. 1. iva the ring and })acking, made large enough to 

 be brought over the measuring ^^essel, J:^C4 a,nd A\ round copper 

 plates provided with a thread and cut out at Ec^ and Ec^ enough 

 to pass over the tube Ei,^, so that they can be put on from the side 

 and made fast together b}" the screws Ec^ ; together they form the 

 closing plate which is screwed into E^^ ; E/^ and Ef., the halves from 

 a round vulcanite plate ^vhicli rest on the ring E,.^ with bottom Ec^ 

 and support the enlargement E^^^. Ef, and E/^ the two halves of a 

 rubber plate which are united hy rul)ber solution and pressed into 

 the ring Ec.^ to make the whole watertight. 



When tlie closing plate has been made fast perpendicularly to 

 the measuring glass and has been screwed against the lower rim of 

 Ea, the two parts of the conical top E,n are brought together into 

 place and the measuring glass centered and held fast by the cork E^. 

 The whole waterbath is then brought into as vertical a position 

 as possible. 



There are windows in the case Ea which enable the tube to be 

 lighted and read. These are formed by thin pieces of plate glass held 

 between stout brass frames Eh, and Eh^ one of which is soldered 

 to the wall of Ea . The screws Eh, enable the plate to be equally pressed 

 against the rubber packing Eh.^ and the glass. It is quite necessary to 

 have the case completely tight, Avliich was here obtained, to prevent 

 the felt in whicli Ea is packed from becoming wet, and hence from 

 an irregular loss of temperature. 



In spite of the verticality of the entire case the glasses require to 

 be tested with a contact spirit level, in order that the necessary 

 correction to the cathetometer reading may be made. 



To determine the volume of an enck)sed quantity of gas the position 

 of the meniscus is not read with reference to the marks on the glass 



43 



Proceedings Royal Acad. Amsterdam. Vol. V. 



