IV. CONDENSATION, ETC. 141 



The eye is kept level with the air chamber. Equality of pressure with the 

 atmosphere is readily obtained by means of the stopper closing the lower 

 bent tube or air chamber. 



638. Compression Pump and Receiver. An apparatus 

 to liquefy and solidify gases. 



H. Lloyd, Trinity College, Dublin. 



640. Apparatus employed in the researches of Dr. Andrews 

 on the continuity of the gaseous and liquid states of matter, and 

 on the properties of matter at high pressure and varied tempera- 

 tures. Dr. Andrews, F.R.S. 



This apparatus consists of two cold- drawn copper tubes of great strength, 

 communicating by horizontal passage, and having massive end-pieces above 

 and below, firmly bolted on with interposed leather washers, so as to be able 

 to resist any pressure. The upper end-pieces are traversed by fine glass tubes, 

 the junction between the glass and metal being made tight by a peculiar 

 system of conical packing. The exposed parts of the glass tubes have a 

 capillary bore, and, if sufficiently fine, will bear a pressure of 500 atmospheres 

 or more without bursting. One of the tubes contains air or hydrogen, and 

 serves as a manometer, the other contains the gas or liquid to be examined. 

 The lower end-pieces carry well hacked steel screws, which produce the pres- 

 sure by compressing the water with which the apparatus is filled. The tem- 

 perature of the air or hydrogen in the manometer, and that of the gas or 

 liquid under examination, can be varied at pleasure by enclosing the glass 

 tubes in outer cylinders of glass, or, where accurate readings are required, in 

 rectangular vessels with plate-glass sides. With this apparatus, accurate 

 measurements can be made to 500 atmospheres, or even higher pressure, and 

 with a slight modification, at any temperature which glass will bear without 

 softening. 



641. Single Apparatus, adapted to exhibit the properties of 

 gases and liquids under different conditions of pressure and tempe- 

 rature, but without measuring the pressures employed. 



Dr. Andrews, F.R.S. 



This apparatus is similar in construction to the compound form last 

 described. 



641a. Original Apparatus, by Desprey, by the help of 

 which he proved the difference, shown by gases, in relation to the 

 law of Mariotte. The Faculty of Sciences, Paris. 



641b. Original Apparatus, by Gay Lnssac, for ascer- 

 taining the elastic force of gases and vapours. 



Polytechnic School, Paris. 



641 c. Apparatus, by M. Dumas, for illustrating the density 

 of vapours. Conservatoire des Arts et Metiers, Paris. 



642. Sulphurous Acid Tube, to exhibit the flickering striaB 

 which occur from slight changes of pressure near the critical point 

 of temperature. Dr. Andrews, F.R.S. 



