84 



MR. W. N. SHAW ON HYGROMETRIC METHODS. 



TABLE II. 



In the first seven experiments the two phosphoric acid tubes were placed first, and 

 in the last five the sulphuric acid tubes were in that position. The columns giving 

 the increase of weight in the different tubes show that these nearly always gained a 

 small amount, but that amount is very irregular, and is about the same whether the 

 phosphoric acid tubes or the sulphuric acid are placed first, and the calculated tension 

 is in nearly every case within 1 per cent, of the tabulated tension. This being about 

 the same error as that which occurs in RKGNAULT'S observations, we may take it that 

 the first tube was sufficient to completely dry the air passed through it, and that the 

 increase of weight hi the other tubes was due to some other cause. 



6. The different connexions were made partly by glass and partly by india-rubber 

 tubing, and this suggested itself as a possible source of the observed differences. A 

 number of observations were therefore taken with a view of determining how far this 

 might be the case. 



I. A glass tube about five feet long was mounted as a connexion between two 

 mercury cups ; and air, first dried by passing through a phosphoric acid tube, was 

 passed through a long glass tube and then through a sulphuric acid tube, and the 

 weight of the latter determined before and after the passage of the air. There was 

 accordingly nothing but the glass tube between the two drying tubes. The results 

 were as follows for four experiments : 



