1890.] Experiments on Vapour-density. 47 



iodide; then came an air-reservoir, M, and a pressure-gauge, O, 

 arranged as shown in the diagram. There were stopcocks at E, L, 

 and N; rubber joints at H, K, and S ; and a screw-clip at R on the 

 tube P, leading to a water-pump. 



Method of Procedure. The capacity of the globe A was accurately 

 determined by weighing the apparatus empty, and then full of water ; 

 it was filled from a wash-bottle, which was also weighed as a check 

 on the other result. 



Pure bromine was specially prepared by boiling commercial 

 bromine with potassium bromide for a day, distilling it through a 

 tube containing red-hot manganese dioxide, and redistilling with 

 phosphoric anhydride ; after a small portion had distilled over, the 

 boiling point was constant at 59'09 (reduced to 760 mm.). Asbestos 

 plugs were found very useful in working with bromine ; by their use 

 a good joint can be secured if liquid bromine is not allowed to come 

 into contact with the asbestos. The thermometer in the distilling- 

 flask was secured by a plug of asbestos, and its bulb was surrounded 

 with asbestos to prevent superheating. 



To commence an experiment, the globe was rinsed with ether, and 

 dried by repeated exhaustion and admission of air ; some bromine 

 was run in without admitting air, the tube above E was fused on to 

 the absorption-tube, F, by means of a portable blowpipe, the liquid 

 in C was boiled, the stopcock E cautiously turned till the pres- 

 sure within the globe was equal to the atmospheric pressure, and 

 then opened from time to time till the bromine ceased to blow out. 

 All the bromine was absorbed in F, which at this stage contained 

 potash solution. The stopcock E and the tube above and below 

 it were gently heated by means of a Bunsen's burner. The absorp- 

 tion-tube was then connected with the reservoir M, and the air 

 was partially exhausted from the whole apparatus ; to complete the 

 exhaustion as far as possible, the globe and the absorption-tube 

 were directly connected with the pump. The stopcock E was then 

 turned off, the tube above it was cracked and removed, more bromine 

 was admitted, the tube fused together again, and the bromine driven 

 out as before till the pressure in A was equal to the atmospheric 

 pressure. The globe was then full of bromine vapour at the 

 atmospheric pressure, and at the temperature of the jacketing 

 vapour, and was ready for a vapour-density determination, or for a 

 series of determinations. The absorption-tube was rinsed out, and 

 partly filled with a strong solution of potassium iodide ; it was then 

 clamped in its place, and connected with the globe A, and with the 

 reservoir M. The water-pump was then set to work till the reservoir 

 was exhausted sufficiently the degree of exhaustion depending upon 

 the number of vapour-density determinations which were to be made 

 in the series. The pump was then cut off by the screw-clip B, and 



