On the .Steam Calorimeter. 



237 



aperture in the inverted cone is about 2 mm. in diameter, that in 

 the lower cone about 3 mm. Their adjustment, therefore, does not 

 present any difficulty, and once made need se^ora be disturbed. The 

 disk resting on the lower cone is permitted to adjust itself. During 1 

 an experiment, it is kept warm by radiation, from the platinum spiral, 

 which is put in circuit with a storage cell. It thus remains dry and 

 quite free to move about on the knife edge of the cone. As the wire 

 swings about, it carries it with it from side to side. Finally, when 

 the amplitude of the vibrations diminish sufficiently, it leaves it 

 correctly adjusted, for, of course, the swinging wire will always so 

 shift the disk as to swing in a diameter of the orifice. This arrange- 

 ment I have found to act very perfectly. The adjustment of the 

 wire in the old arrangement was very troublesome ; it demands no 

 attention with this, which in no way interferes with the weighing. 

 The disk should not be lighter than the weight specified, for if too 

 light the amount of steam pressure which it is necessary to maintain 

 will raise it at one side. 



It is remarkable as regards the platinum spiral for maintaining the 

 orifice dry that an error may be introduced if this is kept at too high 

 a temperature. It apparently then sets up an ebullition of the water 

 precipitated on the upper part of the calorimeter, the result being a 

 splashing or rain upon the substance hanging below. I have been 

 led to suppose this by observing that the radiation effect is apparently 

 increased by heating the spiral excessively. On the other hand, too 

 cold a spiral, of course, also causes error by permitting water to con- 

 dense on the wire both above and below the orifice. The right 

 temperature seems to be that which gives to the spiral a just visible 

 red when steam is not in the calorimeter. The effect of the up draught 

 of steam is to cool it. 



The suspending wire should be of platinum ; about 0*1 mm. 

 diameter will be sufficiently strong for most purposes. This ascends 

 to the left end of the balance beam, being directly attached to a 

 counterpoise equilibrating the right-hand pan. 



It is well to load the balance till there is equilibrium when the 

 empty carrier is in position. The counterpoising of the substance 

 before an experiment then affords its weight, with, of course, the 

 ordinary correction for air displacement, if thought necessary. 



The balance used by me is a Sartorius short-beam (14 cms.). The 

 cheap form of this instrument answers admirably, reading accurately 

 to tenths of milligrams when loaded with over 100 grams. It will 

 do so, I believe, up to 200 grams. It is quick, and in every way is 

 perfect for the purpose. On removing the pan stops the suspending 

 wire may be taken through the drilled aperture left in the plate-glass 

 base. 



The stand of the calorimeter is of well-seasoned mahogany, strongly 



