t)iX0N AND Ball — Heat produced during Inversion, of ^'ucrose. l/)5 



Construction of Thermocouple. 



The thermocouple employed was constructed of copper and eureka wires, 

 according to the method previously described (3), with the exception that 

 the wires leading to the junctions passed through narrow glass tubes 

 instead of being fastened to pine rods. The glass tubes used were 25 cm. 

 long, and the wires, which were well coated with collodion varnish, projected 

 about 1 cm. from the lower ends. The junctions were protected from injury 

 by being attached to little pieces of wood which were pushed into the tubes. 

 The remaining spaces in the tubes were filled with paraffin-wax, whicli 

 effectually sealed them and kept the wires in place. The copper wires of 

 the thermocouple then passed to the reversing switch of the type already 

 described (3). This switch is preferable to a mercury one, owing to complete 

 absence of thermoelectric effects. 



The galvanometer used was of the Ayrton-Mather pattern, giving for one 

 micro-volt a deflection of the spot of light on the screen one metre distant 

 from the mirror, of 10 mm., and for one micro-ampere 206 mm. By means of 

 the reversing switch, readings were always taken on both sides of the middle 

 of the scale, and subtracted from one another to obtain the deflection. This 

 ensures that errors due to movement of the zero or to thermoelectric effects 

 at the junctions of the leads with the galvanometer terminals, are completely 

 eliminated. 



Calibration. 



The thermocouple was calibrated by using it for the determination of tlie 

 freezing-point of a solution of sucrose of definite concentration, according to 

 the method previously described (3). As the depression of freezing-point of 

 solutions of sucrose of different concentrations are known from the researches 

 of Kaoult (5), this affords an easy and accurate method of calibration. 



The thermocouple used was found to give a deflection on the scale of 

 1 mm. per 0-00258° 0. 



Method of Releasing Enzi/me Solution. 



It is obviously essential that the enzyme solution, at the moment of 



mixing, be at exactly the same temperature as the solution on which it is to 



act. This can only be ensured by having it in a container immersed in the 



solution for some time before the commencement of the experiment. It is 



also necessary that the mixing be performed without opening the flasks, 



which might cause a disturbance in temperature of the liquids contained in 



them. In Brown and Pickering's experiments (1) the enzyme solution was 



contained in a glass pipette, the end of which was bent upwards and then 



y2 



