ON EUDIOMETERS. 



BY PROFESSOR MCLEOD. 



.THE name eudiometer was applied to the instruments 

 employed shortly after the discovery of oxygen for 

 measuring the purity of air, which was thought to 

 depend solely on the quantity of oxygen it contained. 

 The name has since been applied to apparatus used for the 

 analysis of gases in general. 



The first attempt at analysing air seems to have been 

 made by Dr. Hales, and is described in his book on 

 "Vegetable Staticks," published in 1727, and which is even 

 now worthy of perusal, although the facts stated by him 

 require a little correction. The apparatus Hales used was 

 more for the formation of gas than the determination of 

 its properties. The apparatus he employed was of this 

 description : At the top was a glass retort, and to it was 

 attached a flask with the bottom removed, called a bolt- 

 head. Generally a glass retort was used, but when certain 

 substances were used which required a high tempera- 

 ture, a gun-barrel was employed. The apparatus was 

 filled with water up to a certain level by putting an 

 inverted syphon into the bolthead, putting it in water, 

 when some air escaped through the syphon. The syphon 

 was then removed and a basin of water placed under 

 the bolthead, when the water remained at a certain 

 level. This level was marked by a piece of string, and 

 heat was then applied to the retort, and in this way the 

 gases appeared. There was a descent of the column of 

 water in the vessel which was marked ~ } and to show the 



