448 PROFESSOR W. DITTMAR ON THE BEHAVIOUR OF THE 



fused carbonate under pressures of about 45 and 60 inches, and analysed these like 

 the rest. 



In all the experiments now to be reported on, the carbonate of lithia operated on was 

 contained in a platinum boat standing in a porcelain tube, which was heated by means of 

 a powerful gas-combustion furnace. The inlet and the outlet tube was provided with a 

 glass stop-cock and inserted by means of a good indiarubber cork. When the pressure 

 within exceeded that of the atmosphere without by not more than 2 inches of mercury, 

 the corks were found to hold tight by friction ; but in the experiments at over-pressures 

 of 1 5 inches or more they would surely have been blown out, had they not been held fast 

 by a suitable arrangement. The contrivance which I used consisted of two perforated 

 iron plates, united into a narrow parallelogram by two iron rods running parallel to the 

 porcelain tube. When the apparatus is used, each of the plates lies flat against the 

 surface of the respective cork, the inlet or outlet tube passing through the perforation. 

 One of the plates is riveted to the rod-ends, the other is adjusted to, and held in, its 

 position by means of thumb-screws. 



In the experiments at higher pressures the outlet tube dipped into a layer of mercury 

 about 2 inches deep ; the entrance-tube communicated, more immediately, with one of two 

 globular mercury-reservoirs united (in the Geisler pump fashion) by means of a long 

 piece of stout indiarubber tubing. This reservoir, I will call it the "working bulb," 

 communicated in its turn with the final outlet of the " Kipp's apparatus," which 

 furnished the stream of dry carbonic acid, the connecting tube being provided with 

 a stop-cock. The other reservoir, the " reservoir proper," sat on a ring of a tall retort- 

 stand, so that it could be placed at greater or less heights. To enable the " Kipp " to give 

 the necessary pressure for driving the gas through the said 2 inches, or occasionally 

 through a greater depth of mercury, the acid in it is adjusted so that, supposing the gas- 

 evolution to have been going on for a while and the outlet tube then to be closed, the 

 acid driven into the upper bulb fills it almost completely ; and this bulb again, by means 

 of a tube fixed in its neck and dipping into the acid, and a piece of indiarubber tubing- 

 slipped over the end of the glass tube, communicates with a bottle having a tubulus near 

 its bottom, through the latter. 



In a given experiment, the first step always was to raise the reservoir so as to fill 

 the working bulb almost completely, and the second to fill the tube with carbonic acid 

 of about 2 inches more than the existing atmospheric pressure, the reservoir being 

 lowered occasionally and re-raised to make sure of all the air being expelled. While a 

 continuous stream of carbonic acid passed through the apparatus, the tube was heated up 

 gradually, so as to expel the moisture from the preparation at the lowest sufficient 

 temperature, but at last brought up to the highest temperature which the combustion 

 furnace would afford. When the carbonate could be presumed to be completely fused, 

 and, under the circumstances, saturated with carbonic acid, the working bulb was, if 

 still necessary, filled as far as possible with carbonic acid. The outlet-tube and the tube 

 connecting the working bulb with the " Kipp " were then closed, and the reservoir 



