HYDRATES AND CARBONATES OF THE ALKALI- METALS, ETC. 445 



weight of the total contents was found to amount to 46L5 grm. ; 212 - 3 grin, of the clear liquor, 

 when titrated with a hydrochloric acid containing 0"02 x HC1 mgrm. per c.c, and dilute baryta- 

 water as an auxiliary reagent, was found to require 1*78 c.c. of the acid for its exact neutralisation, 

 corresponding to 3 - 86 c.c. for the whole, or to - 063 parts of free Li 2 per 100 of original substance. 



Experiment II. — Done in a similar manner to No. I. ; only the temperature was kept 

 at the lowest point, enabling the carbonate to be completely fused. The product, this 

 time, was analysed exactly with chloride of barium, and found to contain 0*018 mgrm. of 

 free Li 2 in 320 mgrm., or 0*0057 per cent. 



Experiment III. — In the case of this experiment the heat was moderated so that the 

 carbonate was near to, but below, its f using-point. The product, when tested with chloride 

 of barium, was found to be perfectly neutral. This method subsequently was largely 

 employed for preparing anhydrous and yet Li 2 0-free carbonate of lithia for other trials. 



Experiment IV. — A platinum boat charged with carbonate of lithia was placed in a 

 combustion tube strengthened by means of a spiral of annealed brass foil wrapped round 

 it, and in it heated by means of a combustion furnace to redness, while a current of 

 carbonic acid was made to pass through the tube, and from it through a layer of mercury 

 2 inches deep. The tube blew out shortly after a red heat had been fairly established, 

 but the product was found to have been in a state of complete fusion, and therefore was 

 analysed by means of chloride of barium. It contained only 0*081 mgrm. of free Li 2 

 in 758 mgrm., or 0*01 percent. I have no doubt in my mind that the product really 

 was neutral, and only became slightly caustic through the sudden removal of the carbonic 

 acid atmosphere at a red heat. Or, in other words, that at the temperature which 

 prevailed in the tube, and probably at any degree of " red heat," the dissociation-tension 

 of carbonate of lithia, though decidedly greater, is only very little greater than 30 inches 

 of mercury. But, to prove this, it was desirable to have a closer approximation to pure 

 Li 2 C0 3 than our Erfurt "purissimum" afforded. I therefore caused Mr Anderson to 

 purify some of this preparation by means of Troost's method, i.e., by dissolving it in 

 water with the help of carbonic acid, and, from the filtered solution, reprecipitating the 

 dissolved salt by removal of the loosely combined carbonic acid at a gentle heat. The 

 crystalline crust thus obtained was washed with small instalments of water, dried at a 

 gentle heat, and preserved for the following experiments. When it appeared desirable to 

 operate upon an anhydrous preparation, a portion of the purified salt was placed in a 

 platinum boat, and kept at a temperature somewhat below its fusing-point, within a 

 combustion tube in a current of dry carbonic acid of ordinary pressure. 



Experiment V. — This was conducted pretty much like the preceding experiment, 

 only with the difference that a porcelain tube was substituted for the glass one. The 

 tube was heated in a combustion furnace, and after attainment of the highest temperature 

 the heating continued for one hour. The depth of mercury through which the carbonic 

 acid bubbled out was 2 inches, and the barometer stood at 29*78 inches ; hence the total 

 pressure of the gas equalled 31 '78 inches. This pressure, at the end of the experiment, 

 was maintained until the product had cooled down considerably below its fusing-point. 



VOL. XXXV. PART II. (NO. 12). 4 E 



