of the Expansibility of a Hard Jena Glass. 127 



It was next transferred to a copper steam-jacket of the 

 ordinary kind used for fixing the boiling-points of thermo- 

 meters, and raised to the boiling-point of water ; the ordinary 

 precautions being taken, and the barometer read in order to 

 apply the correction for reduction to Steam Temperature, at 

 Standard Pressure. 



During this operation a quantity of mercury was driven 

 up into the tube FAC, and this was removed, as before, by an 

 application of the vacuum of the water-pump. The tube was 

 then allowed to cool, and was dried and weighed. 



The whole process was extremely easy ; and the only 

 important source of error was that due to the capillarity of 

 the mercury at the top ; which, with clean glass and clean 

 mercury, and with so large a total quantity of mercury, was 

 very small. Spe2ial care was taken to make the volume of 

 the joint at A as small as possible, in order to minimise this 

 source of error. The operations are much easier than those 

 involved in the handling and weighing of a weight-thermo- 

 meter of the ordinary kind at the ice-temperature. 



The following examples show the numerical results of one 

 of the experiments : — 



Grammes. 



Weight of glass apparatus 83*880 



Weight of apparatus filled with mercury 



to point A, at 0° C 547*28 



Difference, being weight of mercury 



atO°C. . . . . v 463-40 



• Weight of apparatus filled with mercury 

 to point A, at steam temperature 



(Barom. 769*5 mm.) 539*665 



Loss of weight between freezing tem- 

 perature and steam temperature, 

 which was 100°*35 7-615 



Hence the apparent expansion of mercury in this glass, 

 between 0° and 100°, was 



7-615 x 100 n . mr oo 

 4b3*40 x 100'3o 



Subtracting this from the known expansion of mercury 

 between 0° and 100°, viz. 0" 01815, we obtain for the cubic 

 expansion of the glass 0*00177. 



Other numbers obtained in a similar way were as follow : — 



(2) 0*00182. 



(3) 0-00183. 



