338 White — Specific Heats of Silicates and Platinum. 



thus lost was under 0*2 per cent of that in the usual silicate 

 charge. The total resultant effect of this method of dropping 

 is to reduce all its errors to accidental ones, whose magnitude 

 can be gathered from the agreement of results. In a number 

 of test drops with a heat quantity one-fourth that subsequently 

 used, the variations were about 0*3 per cent. Assuming all 

 these to have resulted from the dropping (which is highly 

 improbable), this leaves for the resultant error from this cause 

 less than 0*1 per cent. 



The Calorimeter* — The distinguishing features of the cal- 

 orimeter were mainly determined by its use in connection 

 with the electric furnace. These are: (1) That the customary 

 water jacket around the calorimeter includes a water cover 

 and incloses it completely. This arrangement, however, is 

 much more than a mere protection against the furnace. It has 

 been independently adopted by several workers for deter- 

 minations at ordinary temperatures, f and seems likely to 

 become a customary feature in calorimetry of the greatest pre- 

 cision. The particular form of jacket cover is new, and 

 appears to have some advantages in simplicity and convenience. 

 It is shown in fig. 1. A single body of water is used, the por- 

 tion in the cover being held up by the atmospheric pressure 

 upon the free surface of the water in the jacket. It is made to 

 circulate back and forth between the two by the action of a single 

 propeller. The stirring and circulation are not in the least 

 disturbed when the cover is swung aside to expose the calori- 

 meter. (2) A second distinguishing feature is the use of a 

 very accurate and sensitive multiple thermoelement as a calori- 

 metric themometer. This choice was originally dictated by the 

 fact that the furnace temperature measurement requires a ther- 

 moelement, therefore a potentiometer, and so it was more con- 

 venient to adapt the other temperature measurements to that 

 instrument. The combination of thermoelement and potenti- 

 ometer, however, has also proved advantageous in other ways. 

 In addition to the general advantages of electrical over mer- 

 cury thermometers and an accuracy about as great as that of 

 the best resistance thermometers yet devised, it has the 

 important advantage of readily permitting practically simulta- 

 neous measurements of a number of different temperatures. 

 Its use enabled the determinations to be easily made by a 

 single observer. ( 3 ) A third feature of the calorimeter is the 

 attempt to avoid entirely bodies of uncertain temperature, 

 chief of which ordinarily is the cover, separated by some 



* Preliminary notes on this calorimeter and the methods used with it have 

 been given in Phys. Eev.. xxv, 137, 1907 ; xxviii, 462, 1909. 



fE. Bose and A. Muller., Gott. Nachr. 1906, 278; Beibl., xxxi, 432, 1907. 

 Theodore W. Eichards, S. J. Henderson and H. L. Frevert, Proc. Amer. 

 Acad., xlii, 575, 1907; Zeitschr. phys. Chem., lix, 533, 1907. 



