CONTRIBUTIONS FROM THE CHEMICAL LABORATORY 

 OF HARVARD COLLEGE. 



MODIFICATIONS OF HEMPEL'S GAS-APPARATUS. 



By Theodore William Richards. 



Received October 26, 1901. Presented November 13, 1901. 



The object of this paper is the description of some simple devices which 

 make possible the accurate analysis of gases with a minimum of special 

 apparatus. 



I. Absorbing Pipette. 



The essential feature of Hempel's method is the use of simply con- 

 structed vessels distinct from the measuring burette for the purpose of ab- 

 sorbing successively the various constituents of a gaseous mixture. Hempel 

 used for this end a modification of Ettling's gas pipette, which answers the 

 purpose admirably ; but of course many other combinations of apparatus 

 might be used. The simplest is perhaps a bulb or wide tube inserted 

 over liquid contained in a bottle. In order to prevent the access of air 

 into this bulb from below, it is well to make the lower part of the tube 

 somewhat narrow, and to bend it upward. If desired, the capillary serv- 

 ing to admit the gas may be bent downwards and then upwards, as it is 

 in the Hempel pipette; but with intelligent use of the pinchcock this pre- 

 caution is not necessary. A satisfactory form of the apparatus is illus- 

 trated in Figure 1. 



Fifty cubic centimeters is quite enough gas for analysis, if a suitably 

 narrow burette is used for measurement, hence the receiving bulb of the 

 pipette (A) need not exceed seventy-five cubic centimeters in capacity. 

 The bottle (C) should be capable of holding one hundred and fifty cubic 

 centimetres in this case. 



The " compound pipette " of Hempel may be imitated by the addition 

 at B of another bottle containing water and a levelling funnel, or the 

 same object may be attained merely by connecting to the outlet B a flex 

 ible rubber bulb, such as a child's toy balloon. 

 vol. xxxvii. — 18 



