102 Mr. J. W. Capstick. Ratio of Specific Heats of [June 15, 



sound in the gases. This was determined by Kundt's method, using 

 a double-ended form of apparatus, in all essential features the same 

 as that described in ' Pogg. Ann.,' vol. 135. The tube in which the 

 dust figures were made was 125 cm. long and 26 mm. in diameter, 

 which Kundt showed to be great enough to avoid any lowering of 

 the velocity of sound from the influence of the walls of the tube. 



Lycopodium was used for forming the figures in the hydrocarbons 

 and in methyl and ethyl chlorides, but in the heavier gases it 

 became sticky, and would not move readily, so for these silica was used. 

 To measure the figures a piece of apparatus was constructed, con- 

 sisting of a pair of parallel platinum wires, carried by a framework 

 which slides along a steel scale graduated to millimetres. The tube 

 was placed on \/-shaped supports, parallel to the scale, and between 

 the wires, which were so adjusted that their plane passed through the 

 centre of the nodes. The position of the framework was then read 

 on the scale, tenths of a millimetre being estimated with the help of 

 a lens. With figures of average quality the setting of the wires 

 could be repeated so as to agree within two or three tenths of a 

 millimetre. The greatest divergence of the observed length of any 

 one figure from the mean of the series was usually about five or six 

 tenths of a millimetre. 



The calculation of the ratio of the specific heats from the velocity 

 of sound requires the density of the gas to be known, a circumstance 

 which makes the method very sensitive to small amounts of impurity 

 in the material. 



Regnault's value of the density was used for methane, and every 

 precaution was taken to sec are pure gas. Two methods of preparation 

 were used, Gladstone and Tribe's, by the action of the copper-zinc 

 couple on methyl iodide and alcohol, and Frankland's, by the action 

 of zinc methyl on water. After each experiment an analysis of the 

 gas was made to test its purity and to determine the amount of air 

 present, for which a correction was made. 



The ethane was prepared by the action of zinc ethyl on water, and 

 for it the theoretical density calculated from the molecular weight 

 was used. 



For the preparation of propane, isopropyl iodide was reduced by 

 zinc and hydrochloric acid, and the gas was freed from air by lique- 

 faction in a freezing mixture of ether and solid carbonic acid, after 

 passing through fuming sulphuric acid and potash, and over 30 grams 

 of palladium. 



Methyl and ethyl chlorides were prepared in the usual way, by 

 passing hydrochloric acid into a boiling solution of zinc chloride in 

 the corresponding alcohol, and purified by redistillation through 

 suitable reagents. All the rest of the compounds were purchased 

 from Kahlbaum, and were dried and fractionated before being used. 



