SCIENCE- GOSSIP. 



NEW PHYSICAL APPARATUS. 



By James Quick. 



rjl comply with the continually increasing de- 

 -'- mancl, chiefly from Secondary and Organised 

 Science Schools, for simple pieces of apparatus to 

 illustrate the fundamental laws of physics, various 

 useful forms have been constructed. 



Fig. 1. — Boyle's Law Apparatus. 



The following, designed by Mr. W. Kheam, B.Sc, 

 Senior Physics Master, Liverpool Institute, have 

 been found very serviceable in elementary practi- 

 cal work in physics. Although they are of simple 

 construction, they nevertheless are capable of 

 giving good quantitative results, which are now 

 so essential in nearly all physical laboratory work. 



sponding decrease in the volume. This rela- 

 tion is set forth by Boyle's law, which states that 

 " the pressure of a given mass of gas at a constant 

 temperature is inversely proportional to its volume." 

 Fig. 1 shows a simple arrangement for exhibiting 

 the law. It consists of a long glass tube of small 

 bore, closed at one end and fixed to a graduated 

 scale of boxwood, which is supported upon a firm 

 wooden base, and which can be rotated about a 

 central horizontal axis. A thread of mercury is intro- 

 duced into the tube by means of a pipette. When the 

 tube, and therefore the mercury thread, is in a 

 horizontal position, the air contained will only be 

 subjected to atmospheric pressure. As the tube is 

 rotated towards a vertical position the mercury will 

 exert an increasing pressure upon the air, and the 

 value will be obtained by measuring the vertical 

 distance between the two ends of the thread. This 

 pressure added to that due to the atmosphere will 

 be the total pressure upon the air. The volumes of 

 the contained air corresponding with these different 

 pressures are also noted during an experiment. The 

 product of the two corresponding values will be 

 found to be a constant quantity, or P V = constant, 

 thus proving Boyle's law. 



Belation between Temperature and Pres- 

 sure op a Gas maintained at Constant 

 Volume. 



Another law closely related to that of Boyle is 

 the one known as Charles' law, which states that 

 " the volume of a given mass of any gas, at constant 

 pressure, increases for each rise of temperature of 

 1° C. by a constant fraction (nearly ^rs) °£ ^ s 

 volume at 0° C." By combining both laws we ar- 

 rive at the statement that if the volume of a gas 

 remains constant, but the temperature and pressure 

 vary, then the pressure is proportional to the tem- 

 perature when the latter is reckoned from the 

 absolute zero, i.e. — 273° C. In other words, "the 



Fig. 2.— Apparatus to Show the Relation between P and T ; V being Cons 



Simple Form op Apparatus for proving 

 Boyle's Law. 



If any gas is kept at a constant temperature and 

 the pressure upon that gas is changed, its volume 

 will also be changed in such a manner that any 

 increase in the pressure will result in a corre- 



pressure of a gas at constant volume increases by a 

 constant fraction (^3) of the pressure at the 

 freezing point for each rise of temperature of 1° C. 

 Fig. 2 depicts an arrangement for showing this 

 relation. 



The gas to be experimented on is confined in a 

 vertical glass tube about 10 centimetres long, and 



