182 THE EARL OF BEEKELEY, MR. E. G. J. HARTLEY AND DR. C. V. BURTON: 



pressure and density of water vapour in air, which are used in the reduction, may be 

 somewhat in error.* It is, therefore, thought advisable to give somewhat full details 

 of the various devices tried and of the test experiments made. 



Improvement in the Apparatus^ and Test Experiments. 



Method of keeping the Bath at C. A large wooden tub was kept filled with ice 

 and water ; a small water pump, actuated by the laboratory shafting, pumped the 

 water from the tub into the bath, and this water syphoned back into the tub. The 

 temperature on a long run varied from about 0"2 to 1'0 C. It may be pointed out 

 that the constancy of the temperature is not of so much importance as that there 

 should be no difference between the temperatures of the various vessels in the bath. 

 This was ensured by stirring the bath very vigorously and continuously. A ther- 

 mometer placed in different positions in the bath showed no variation. 



Limits of Accuracy of Weighing the Glass Vessels themselves. 



One of the vessels was weighed four times, at intervals of a week or so, against the 

 counterpoise, various operations having been performed on it between while, with the 

 following results : 



Weight of vessel before experiment, 377925 gr. ; after, 377925, 377925, 

 377923 gr. 



Another vessel, fitted with mercury cups (see infra, fig. 3, p. 186), was similarly 

 weighed. The cups, after mercury had been poured into and out of them, were 

 cleaned witli nitric acid, dried with alcohol, &c. : 



Weight of vessel before experiment, 29 '2700 gr. ; after various washings and 

 leaving in the bath for a week, 29'2760, 29'2759, 29'2759, 29'2758, 29'2760, 

 29-2756, 29-2755 gr. 



The change shown in the last two experiments is probably due to the balance 

 wanting cleaning. From these numbers it will be seen that the maximum error is 

 only G'0005 gr. 



New Form of Joint between Water and Sulphuric Acid Vessels. 



The method adopted for measuring the relative lowering of the vapour pressure of 

 the solution is that described in the ' Roy. Soc. Proc.' (BEKKELEY and HARTLEY, 

 vol. 77, A, 1906). The solution is contained in two vessels which are weighed 

 separately. Dried air passes over the solution in these vessels in series; it then passes 

 over water in a weighed vessel, and finally over sulphuric acid in a fourth weighed 

 vessel. The assumption on which the method is based is that the air, on emerging 



* The values are derived from REUNAULT'S work, but he himself seems somewhat dissatisfied with them, 

 t Described 'Roy. Soc. Proc.,' vol. 77, A, 1906, pp. 156, 162. 



