SPECIFIC GRAVITY OF HYDROGEN GAS. 67 



Biot and Arago, and Allen and Pepys ; Saus- 

 sure's errors and my own, being in excess, can 

 only be explained by a mistake in the weighing. 

 My own, indeed, is accurate as far as my balance 

 could enable me to go. The quantity of oxygen 

 gas weighed, amounted to 20 grains, and the 

 smallest weight I used was riuth of a grain ; con- 

 sequently, I could only estimate the weight with- 

 in aoVoth part : the three first decimal places I 

 could depend on, but not upon the fourth ; ac- 

 cordingly the fourth decimal place was too high, 



SECT. III. 



OF THE SPECIFIC GRAVITY OF HYDROGEN GAS. 



I GOT a thin glass flask blown, with a flat bot- Method f 



' e determin- 



tom and a narrow cylindrical mouth, into which ing the Sp2 , 

 the extremity of a bent glass tube was ground, of hydro- 7 

 so as to fit it accurately. The capacity of the gen gas ' 

 flask was about 18 cubic inches ; the tube was 18 

 inches long, and the diameter of its interior 

 cavity about the fifth of an inch. Its two 

 extremities were bent nearly at right angles 

 with the body, and turned different ways as 

 here represent- . , . _ -/J 



ed ; a being the i 

 end which was 



ground into the mouth of the flask. The whole 



E 2 



