272 DR. R. ANGUS SMITH ON AN APPARATUS FOR 



Professor Bunseii has directed his talents to this, and has 

 improved the plan to a great degree, but I cannot think 

 that he has completely succeeded. As far as 1 understand 

 his apparatus, as described by Dr. Hoffmann in the Journal 

 of the Chemical Society of London, there is still a great 

 amount of steam carried over with the air, which condensing 

 above the mercury must lead to absorption and to error. 

 In fact, his principle is to carry the air over by a superabund- 

 ance of watery vapour. Then he makes a globe with all its 

 joints and attachments stand the pressure of the atmosphere, 

 which is of itself a dangerous experiment, so readily do these 

 joints give way and allow air to pass. For these reasons and 

 because of its complicated structure, I have not used the 

 apparatus of that eminent chemist. 



One of my earliest trials was the following; it may be 

 useful to describe it, as it will shew what reason I have for 

 avoiding pressure as much as possible. The flask in which 

 the water was boiled was connected by a bent tube with a 

 vessel of mercury, on the upper part of the bend a tube was 

 attached exactly in the manner now used, and which will be 

 seen by the woodcut. When the apparatus was filled with 

 water, and heat applied, the mercury of course yielded and 

 acted like a safety valve. Sometimes, however, it rose too 

 high or sunk too low, and the pressure of a very small 

 column was sufficient to cause air to enter by the joinings, 

 even after they were bound in the most careful manner with 

 strong wire. Another objection was, that over the mercury 

 a certain amount of water was placed, which did not suf- 

 ficiently diffuse itself amongst the rest, but remained com- 

 paratively cool. This might have been avoided by heating 

 the mercury also, had not a readier plan presented itself. 



The principal feature of the method adopted is that of 

 regulating the varying pressure which results from boiling, 

 and from the generation or escape of the gases, by a balloon 

 capable of dilatation and contraction. By the use of this 



