400 PROFESSOR W. DITTMAR ON THE BEHAVIOUR OF THE 



lowest sufficient temperature in carbonic acid would make a capital standard substance 

 for the purposes of alkalimetry ; I therefore caused Mr Anderson to prepare a fresh 

 quantity, and determine its degree of hygroscopicity by quantitative experiments. He 

 fused a quantity of perfectly pure carbonate made from oxalate over a Bunsen for one 

 hour in carbonic acid, and allowed the fuse to freeze in the crucible. It was then taken 

 out, broken into small fragments, and two separate quantities of these weighed out, 

 namely, one amounting to several grammes on a watch glass, and another in a stoppered 

 preparation tube. The watch glass was allowed to stand uncovered in the balance 

 case, and weighed from time to time. After forty-five hours it had gained 0*2 mgrm. 

 After having been allowed to stand for other seven days, it had gained 4 '6 mgrm. 

 The contents of the preparation tube during all the time had gained only 1 mgrm. 

 The substance, as we see, is so little hygroscopic that, supposing it to be preserved in not 

 too small fragments in a well-stoppered bottle, its weight could be relied on as remaining 

 constant for a long time. 



At the very high temperature producible in a platinum crucible by means of a 

 blowpipe, carbonate of soda loses carbonic acid even in an atmosphere of dry C0 2 , perhaps 

 through rapid diffusion-in of H 2 . So at least it appears from the following experiment, 

 which was made long before No. (11) : — 



Experiment (12). — 3 "1277 grm. of dry carbonate of soda (Erfurt purissimum) were 

 placed in the hydrogen-crucible and heated in dry carbonic acid, first for two hours over 

 a large Bunsen, then for other two hours over the gas blowpipe. The product was analysed 

 with the following results — : 



27866 grm. gave 1*1497 of C0 2 and 3731 of Na 2 S0 4 , corresponding to 41 '258 percent, 

 of carbonic acid and to 58*491 per cent, of oxide of sodium ; total = 99749. The deficit 

 of 0*251 per cent., if not due to errors, must be put down as water. By combining the 

 carbonic acid with what it needs of Na 2 to become Na 2 C0 3 , and calculating the rest of 

 the Na 2 as NaOH, we have — 



Carbonate of soda, . . . . . 99-498 



Hydrate of soda, NaOH, 0-324 



Water, 0178 



100-000 



Normal carbonate of soda contains, by calculation, 41*47 per cent, of C0 2 and 58*53 

 per cent, of Na 2 0. Unfortunately the chloride of barium method was not yet worked out at 

 the time, so that the existence of caustic alkali in the substance was not proved directly. 



Experiments with Carbonate of Potash. 



A supply of " Kali carbonicum purissimum " from Trommsdorf of Erfurt, when 

 tested qualitatively, turned out to be so nearly pure that it might safely have been used 

 for the experiments as it stood ; but on the principle of good is good and better is better, 



