﻿164 Prof. R. Bunsen's Calorimetric Researches. 



after filling along with the perfectly dry glass point, the weight 

 of the enclosed water is obtained. The open limb is then com- 

 pletely filled with boiled mercury by means of a long capillary 

 glass tube, which prevents air-bubbles adhering to the sides of 

 the tube. If the apparatus be now exposed in the open air to a 

 temperature under 0° C, an ice-cylinder is formed which at last 

 partly closes up, leaving a thin column of water unfrozen. By 

 freezing this last portion of water the ice already formed is ex- 

 posed to very great pressure, which sensibly alters its specific 

 gravity ; this pressure is so great that it can burst a glass tube 

 able to resist a pressure of 80 atmospheres. 



To remove this irregularity, and to allow the formation of ice 

 during the whole experiment to take place under the same pres- 

 sure, it is simply necessary to surround the whole instrument 

 with sawdust and to expose only the upper part at a to an air 

 temperature under 0° C. After a mass of ice has been formed 

 at a by exposure to a low temperature, it is allowed to melt, with 

 the exception of a small portion in the centre ; and the freezing 

 then proceeds regularly downwards from a to b, and can be very 

 conveniently regulated if the limb containing the water is gradually 

 raised as required out of the sawdust. The cylinder of ice forms 

 a half-spherical cavity at its base, which proceeds unchanged till 

 the level of the mercury at b is reached and the last portions of 

 water are frozen from above to below. As soon as the formation 

 of ice ceases, the whole apparatus is exposed for some time to a 

 temperature under 0° C, so as to freeze the last traces of water 

 which are found at b between the mercury and the glass. The 

 cylinder of ice thus formed, perfectly free from air-bubbles, resem- 

 bles the purest crystal for clearness and transparency. By tightly 

 inserting the cork (e) in the open limb of the apparatus (A), the 

 tube B is joined to A ; and no trace of air must remain between 

 the cork and the mercury, which is forced by the pressure through 

 the capillary tube (/) into the vessel (B) containing mercury to 

 the level g. The capillary tube is secured with the finest sealing- 

 wax into the cork, which must be smooth and perfectly free from 

 pores. It is quite unnecessary to secure the cork in the wider 

 tube also with sealing-wax, since a displacement of this is as little 

 to be feared as an elastic rebound (elastiche Nachwirkung) ; I have 

 convinced myself of this by direct experiments. The apparatus so 

 arranged is placed in a room with as constant a temperature as pos- 

 sible, and surrounded on all sides and over the cork with a thick 

 layer of snow, which has not lain at a temperature aboveO°and be- 

 come impregnated with moisture, but which is dry and coherent. 



If the apparatus has assumed a temperature of 0° C. after 

 standing six or twelve hours, the mercury-vessel is removed from 

 the cork (h) and weighed with the mercury it contains, and re- 



