ON EUDIOMETERS. 283 



Dbbereiner, who discovered the curious action of spongy 

 platinum on a mixture of hydrogen and oxygen, proposed 

 to determine the oxygen in the air by introducing into a 

 mixture of hydrogen and air spongy platinum made up 

 into balls with clay. This gives concordant results, but 

 there is a little difficulty about applying it, and it is 

 therefore not much used, especially as we now know that 

 the explosion method is superior to all others. 



All those processes which I have described at present, 

 refer to the determination of oxygen only, but this was 

 not by any means all that was required ; it was necessary 

 to go very much further than to determine only one gas, 

 and in the Philosophical Transactions for 1803, Hope 

 described an instrument, of which there is a remnant here 

 taken from the collection, of Dalton's apparatus. It 

 consists of a graduated tube (the upper portion of which 

 is unfortunately broken off) divided into ten parts, con- 

 taining two cubic inches, and there is a small bottle fitted 

 by grinding to the lower end. The bottle is filled with a 

 liquid absorbent, which for oxygen might be a solution of 

 hepar sulphvris or a solution of ferrous sulphate saturated 

 with nitric oxide, which answers perfectly. This having 

 been filled is closed with a ground-glass plate, and then 

 placed in the pneumatic trough. The graduated tube con- 

 taining air is put over the bottle, the plate removed, and 

 the tube introduced into the ground neck. You then 

 have a measured quantity of gas in contact with the 

 liquid in a perfectly air-tight vessel. The apparatus is 

 inverted and shaken about ; it is introduced once more 

 into the water, and the side stopper below is slightly 

 opened ; this causes an introduction of some water to 

 replace the gas which has been absorbed, and the process 

 is continued until no more absorption takes place. The' 

 residual volume in the case of air would be nitrogen, but 

 this apparatus may be employed for the determination 

 of other gases besides oxygen. Henry afterwards employed 

 an india-rubber bottle instead of the glass bottle, which 

 enables you to introduce the liquid absorbent into the gas 

 with great ease. 



But there was a great improvement made in this 

 apparatus by Pepys, who made a number of most impor- 

 tant experiments on gases in general, most of which he 



