418 



willi it. ir I lie Welter is sucked cautiously into the burette, the 

 effective pressure once made is preserved in )v. 



Another error arises, when the burette is exposed to oscillations 

 of temperature in the laboratory-. In that case not only in in, bnt 

 also in z and ?», falls and rises occur, whicli are not due to ab- 

 sorption of oxygen. This may be prevented by keeping the burette 

 likewise at a constant temperature, which may be attained as follows. 



By means of a metal sucking- and forcing-pump zp (likewise 

 fastened to the copper frame, to which the whole apparatus is 

 fastened) water from (he thermostat is pumped up with great 

 rapidity into a wide glass cylinder iva, which contains the burette. 

 The water enters )ua at the bottom and is led back to the thermo- 

 stat at the top through the tube af. Even at high teiriperature (50°, 

 55° C), the temperature in the burette is kept eijual to that of the 

 water in the thermostat in this way. 



/'. The regulation of tJie tt^in/ifrutiire principally corresponds to 

 the one described by Rutgehs ') and Cohen STt'AKT') and is an 

 imitation of apparatus, used in the van 't HuFi-laboi'atory at Utrecht. 



The heating-apparatus v (fig. 7) consists of a copper case, sur- 

 mounted by a metal tube, rising above water. In v is paraffine-oil, 

 electrically healed by a nickel-chronie-wire, wrapped round a piece 

 of mica. 



Thermoregnlalor /!, stirring-apparatus r and v, are close together 

 in an open glass cylinder c, resting on legs in the centre of the 

 thermostat y. To prevent all influence of vibration in the height of 

 the mercury, the ihermoregulator is hung fi'om the ceiling on a 

 steel spiral-spring, according to the method Moll. 



The method described above gives no new principle, with respect 

 to the C(),-determination. We have chosen the simple and always 

 trustworthy baryta-method, which need not be further described 

 here. On account of the insertion into a closed system, the various 

 parts were subjected to some alterations in shape, which however 

 have nothing to do with the principle of the baryta-method. 



The problem of oxygen-supply, ever yielding many difficulties, 

 could be satisfactorily solved. Compared with the methods ') already 

 existing, the following advantages and simplifications are achieved: 



^) Rutgers, A. A. L., Recueil des Travaux Botaniques Néerlandais. Vol. iX, 

 1912, pag. 1. 



') Cohen Stuart, Recueil des Travaux Botaniques Néerlandais. Vol. XIX. 

 Livraison 2. 1922. 



') Cf. Krogh: 'The respiration exchange of animals and man. Longmans, 

 GuKKN and Co., London 1916". 



